Nonlinear compensation in bandpass filter

Abstract

To provide a bandpass filter with nonlinear compensation.SOLUTION: In a bandpass filter 250, a current control circuit with controlled current variation includes: an amplifier 204 having an input terminal and an output terminal; capacitors 210, 212 each having a first terminal and a second terminal, the first terminal being coupled to the input terminal of the amplifier, the second terminal being coupled to the output terminal of the amplifier; and diode circuit elements 214, 222 each having a first terminal and a second terminal. The first terminal of each diode circuit element is coupled to the first terminal of corresponding capacitor and the input terminal of the amplifier, and the second terminal of each diode circuit element is coupled to the second terminal of corresponding capacitor and the output terminal of the amplifier.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates generally to circuits, and more particularly to bandpass filters including nonlinear compensation. [Background technology]

[0002] A bandpass filter is an electrical component that blocks low and high frequency signals and allows signals within a certain frequency range to pass. Bandpass filters are used in a wide range of fields, such as medical imaging, telecommunications, data transmission, and / or other fields that use analog signals. In some examples, a bandpass filter is implemented by a feedback system that includes two back-to-back integrators. The integrators may be implemented by amplifiers (e.g., differential amplifiers, fully differential amplifiers, etc.) in conjunction with other components (e.g., resistors, capacitors, etc.). Summary of the Invention

[0003] In at least one example of the present description, a circuit includes an amplifier having an input terminal and an output terminal; a capacitor having a first terminal and a second terminal, where the first terminal of the capacitor is coupled to the input terminal of the amplifier and the second terminal of the capacitor is coupled to the output terminal of the amplifier; and a diode circuit element having a first terminal and a second terminal, where the first terminal of the diode circuit element is coupled to the first terminal of the capacitor and the input terminal of the amplifier and the second terminal of the diode circuit element is coupled to the second terminal of the capacitor and the output terminal of the amplifier. [Brief description of the drawings]

[0004] [Figure 1] 1 is an exemplary medical imaging machine for implementing bandpass filters associated with the examples described herein.

[0005] [Diagram 2]2 is an example fully differential implementation of the bandpass filter of FIG. 1.

[0006] [Diagram 3] 3 is an example fully differential circuit implementation of the bandpass filter of FIG. 2.

[0007] [Figure 4] 2 is an example differential implementation of the bandpass filter of FIG. 1.

[0008] [Diagram 5] 2 is an example alternative fully differential implementation of the bandpass filter of FIG. 1.

[0009] [Figure 6] 6 is an example fully differential circuit implementation of the bandpass filter of FIG. 5.

[0010] [Figure 7] 2 is an exemplary alternative differential implementation of the bandpass filter of FIG. 1.

[0011] [Figure 8] 2 is an example alternative fully differential implementation of the bandpass filter of FIG. 1.

[0012] [Figure 9] 9 is an example fully differential circuit implementation of the bandpass filter of FIG. 8.

[0013] [Figure 10] 2 is an exemplary alternative differential implementation of the bandpass filter of FIG. 1.

[0014] [Figure 11] 11 is a flowchart illustrating methods and / or operations that may be performed by the bandpass filters of FIGS. 1, 2, 3, 4, 5, 6, 7, 8, 9, and / or 10.

[0015] [Figure 12]FIG. 2 is an example timing diagram described in connection with the examples described herein.

[0016] In the drawings, the same reference numbers or other reference designators are used to refer to the same or similar (functional and / or structural) features. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The drawings are not necessarily drawn to scale. Generally, the same reference numbers and their descriptions in the drawings refer to the same or similar parts. Although regions are illustrated in the drawings with complete lines and boundaries, some or all of these lines and / or boundaries may be idealized. In reality, the boundaries and / or lines may be unobservable, blended, and / or irregular.

[0018] Some bandpass filters use a feedback system with two successive integrators. A bandpass filter allows signals to pass a certain frequency range defined by a center frequency and a bandwidth. The center frequency (referred to herein as ω0) is the frequency at which the bandpass filter gain is the set passband gain. The bandwidth (BW or ω0) of a bandpass filter is the B ) corresponds to the frequency range above and below the center frequency that a signal can pass with less than X (e.g., 3) db of attenuation, e.g., minimum and maximum frequencies corresponding to a threshold amount of gain below the center frequency gain. The bandwidth of a bandpass filter is characterized by a quality value (Q). The quality value or quality factor of a bandpass filter is the center frequency divided by the bandwidth (Q=ω0 / ω B ). For a given center frequency, a higher quality value corresponds to a narrower passband and a lower quality value corresponds to a wider passband.

[0019] As mentioned above, a bandpass filter may have two successive integrators. For example, a Tow-Thomas bi-quad bandpass filter includes two successive integrators. To control the characteristics (e.g., center frequency and / or bandwidth) of the bandpass filter, the bandpass filter can be implemented with a lossy integrator (also referred to as a real integrator) and a lossless integrator. A lossless integrator includes an amplifier with one input terminal coupled to an output terminal via a capacitor and does not include a feedback resistor. A lossy integrator includes an amplifier with one input terminal coupled to an output terminal via a parallel capacitor and resistor (e.g., a feedback resistor). Both types of integrators include a resistor (e.g., an input resistor) coupled to the input of the amplifier. The transfer function of a lossy integrator is: TIFF2025013753000002.tif511, where R1 is an input resistor, R2 is a feedback resistor, C is a capacitor, and s is a complex variable corresponding to the relationship between the output and input of a lossy input system. Since the transfer function of the lossy integrator corresponds to the resistance of the resistor, a resistor having a particular resistance can be selected to control the center frequency and / or bandwidth of the bandpass filter. For example, the quality and / or bandwidth of the bandpass filter is based on the selected resistance of the feedback resistor.

[0020] As mentioned before, bandpass filters include a feedback loop. Therefore, bandpass filters can be unstable if not properly designed. Bandpass filters can also exhibit signal-dependent stability behavior. Therefore, simple small signal stability is not sufficient to ensure filter stability over the complete operating voltage amplitude range. Bandpass filter instability can result in persistent oscillations at the output of the bandpass filter when the amplitude of the input signal is too high, e.g., due to noise and / or the characteristics of the device generating the input signal. The stability of a bandpass filter depends on the frequency of the non-dominant pole for the bandpass filter and the unity gain crossover point of the bandpass continuous integrator loop. The non-dominant pole of a bandpass filter is determined by the ratio of the center frequency to the quality factor (e.g., ω c / Q). The unity gain crossover point (also called unity gain crossing) is the frequency at which the lossy integrator gain is 0 dB. The phase loss contribution of the non-dominant pole of the back loop at the unity gain crossover point reduces the phase margin of the loop, thereby reducing the stability of the bandpass filter. For example, the closer the frequency of the non-dominant pole is to the unity gain crossover point, the more the phase of the non-dominant pole contributes to the phase margin at the unity gain crossover point, which corresponds to a less stable system.

[0021] The examples described herein increase the stability of the bandpass filter by decreasing the feedback resistance of the lossy integrator in response to the input voltage exceeding a first threshold or falling below a second threshold. The DC gain of the lossy amplifier is a function of the feedback resistance (e.g., -R2 / R1). The DC gain corresponds to the quality factor (Q) of the filter and determines the unity gain crossover of the feedback loop. Also, as previously mentioned, the frequency of the non-dominant pole is a function of the quality of the lossy integrator, which is a function of the feedback resistance. Thus, by decreasing the feedback resistance in response to the input voltage exceeding a maximum threshold (or falling below a minimum threshold), the frequency of the unity gain crossover point decreases to a lower frequency and the frequency of the non-dominant pole increases in frequency, increasing the distance between the two frequencies. Therefore, the phase contribution of the non-dominant pole has a smaller (or zero) effect on the phase margin of the unity gain crossover point to increase the stability of the bandpass filter. The examples described herein use a diode circuit as feedback for a lossy integrator to reduce the feedback resistance of the lossy integrator in response to the input voltage exceeding a threshold, as described further below. The examples described herein result in a stable system that is reliable and provides fast overload recovery in the bandpass filter.

[0022] FIG. 1 illustrates an image scanning machine 100. The image scanning machine 100 of FIG. 1 includes an example image capture component 102, an example front-end amplifier state circuit element 104, an example bandpass filter 106 (also referred to as a bandpass filter circuit or bandpass filter circuit element), an example analog-to-digital converter (ADC) 108, and an example image processing circuit element 110. Although the bandpass filter 106 is implemented in the image scanning machine 100 of FIG. 1, the bandpass filter 106 may be implemented by itself (e.g., in a dedicated circuit or IC) or in any circuit in which a bandpass filter is desired, such as audio processing, image processing, telecommunications, automotive systems, and / or any other type of electronic machine that may include a bandpass filter. The image scanning machine 100 of FIG. 1 is a medical image scanning machine, such as a magnetic resonance imaging (MRI) machine, an ultrasound machine, etc. However, the image scanning machine 100 may be any type of image scanning machine. Although the illustrated components are connected via two connections (e.g., an inverting connection and a non-inverting connection), the components may be connected via a single connection. The non-inverting connection corresponds to an analog signal generated by the image capture component 102. The analog signal is referred to herein as the non-inverting input signal. The inverting connection corresponds to an inversion of the analog signal generated by the image capture component 102. The inversion of the analog signal is referred to herein as the inverting input signal.

[0023] The image capture component 102 is a sensor and / or transducer that transmits and / or receives signals to generate an image. For example, in an ultrasound system, the image capture component 102 transmits sound waves into the body. The image capture component 102 then receives or senses the reflected sound waves reflected from the body tissue. In an MRI system, the image capture component 102 generates a magnetic field and detects the energy released when protons realign with the magnetic field. The image capture component 102 transmits one or more analog signals corresponding to an image to the front-end amplification state circuit element 104. The front-end amplification state circuit element 104 is an instrumentation amplifier topology that amplifies the signal from the image capture component 102. The front-end amplification state circuit element 104 outputs the amplified image signal to a bandpass filter 106.

[0024] The bandpass filter 106 of FIG. 1 filters high frequency signals (e.g., signals above a first frequency threshold) and low frequency signals (e.g., signals below a second frequency threshold). As described further hereinafter, the bandpass filter 106 reduces the feedback resistance in response to the input signal exceeding a maximum threshold amplitude (or falling below a minimum threshold amplitude), thereby decreasing the frequency of the unity gain crossover point and increasing the frequency of the non-dominant pole. The difference between the frequency of the unity gain crossover point and the frequency of the non-dominant pole is increased so that the phase contribution of the non-dominant pole has less impact on the phase margin unity gain crossover point. As described above, reducing the impact of the phase contribution of the non-dominant pole on the phase margin of the unity gain crossover point increases the stability of the bandpass filter 106. The bandpass filter 106 outputs a filtered output to the ADC 108. ADC 108 converts the filtered analog signal to digital values ​​that are used by image processing circuitry 110 to generate an image that can be output by an interface (e.g., a user interface). Bandpass filter 106 is described further below in conjunction with Figures 2-10.

[0025] 2 is an example circuit diagram of an example bandpass filter 250 for implementing the bandpass filter 106 shown in FIG. 1. The bandpass filter 250 of FIG. 2 includes an example lossy integrator 200 and an example lossless integrator 202. As mentioned above, the lossy integrator includes a feedback resistor coupled in parallel to a feedback capacitor. On the other hand, the lossless integrator includes only a feedback resistor. The lossy integrator 200 includes an example fully differential amplifier 204, example resistors 206, 208, example feedback capacitors 210, 212, example diode circuit elements 214, 222, example diodes 216, 220, 224, 228, and an example resistor 218. The example bandpass filter 250 further includes feedback resistors 230, 232. The fully differential amplifier 204 has both a differential input and a differential output.

[0026] The output of the example front-end amplifier state circuitry 104 is coupled to an input terminal of a lossy integrator 200. The output terminal of the lossy integrator 200 is coupled to an input terminal of a lossless integrator 202. The output terminal of the lossless integrator 202 is coupled to the input terminal of a fully differential amplifier 204 via feedback resistors 230, 232.

[0027] The fully differential amplifier 204 of FIG. 2 amplifies an input signal. The fully differential amplifier 204 has two input terminals (e.g., an inverting input terminal and a non-inverting input terminal) and two output terminals (e.g., an inverting output terminal and a non-inverting output terminal). A first input terminal (e.g., an inverting input terminal) of the fully differential amplifier 204 is coupled to a second terminal of the resistor 206, a first terminal of the resistor 230, a cathode terminal of the diode 216, a first terminal of the resistor 218, an anode terminal of the diode 220, and a first terminal of the capacitor 210. A second input terminal (e.g., a non-inverting input terminal) of the fully differential amplifier 204 is coupled to a first terminal of the resistor 232, a cathode terminal of the diode 224, a first terminal of the resistor 226, an anode terminal of the diode 228, and a first terminal of the capacitor 212. A first output terminal (e.g., a non-inverting output terminal) of the fully differential amplifier 204 is coupled to the ADC 108, a first input terminal of the lossless integrator 202, an anode terminal of the diode 216, a second terminal of the resistor 218, a cathode terminal of the diode 220, and a second terminal of the capacitor 210. A second output terminal (e.g., an inverting output terminal) of the fully differential amplifier 204 is coupled to the ADC 108, a second input terminal of the lossless integrator 202, an anode terminal of the diode 224, a second terminal of the resistor 226, a cathode terminal of the diode 228, and a second terminal of the capacitor 212.

[0028] The input resistors 206, 208 of the lossy integrator 200 of FIG. 2 have two terminals. A first terminal of the resistors 206, 208 is coupled to the front-end amplification state circuit element 104. A second terminal of the resistor 206 is coupled to a first terminal of a resistor 230, a cathode terminal of a diode 216, a first terminal of a resistor 218, an anode terminal of a diode 220, a first terminal of a capacitor 210, and a first input terminal of the fully differential amplifier 204. A second terminal of the resistor 208 is coupled to a first terminal of a resistor 232, a cathode terminal of a diode 224, a first terminal of a resistor 226, an anode terminal of a diode 228, a first terminal of a capacitor 212, and a second input terminal of the fully differential amplifier 204. The resistances of the resistors 206, 208 can be selected based on a desired gain of the lossy integrator 200. The non-inverting input signal from the front-end amplification state circuitry 104 is received via resistor 206, and the inverting input signal from the front-end amplification state circuitry 104 is received via resistor 208. The resistance of resistors 206, 208 may be selected for a desired quality value (Q) and / or a desired bandpass gain (Av).

[0029] 2 shorts out and bypasses the resistance of the respective resistors 218, 226 and / or the resistance of the respective diodes 216, 220, 224, 228 for high frequency signals. The resistance of the resistors 218, 226 can be selected for a desired quality value (Q). The capacitors 210, 212 also reduce the gain of the amplifier 204. A first terminal of the capacitor 210 is coupled to a first terminal of a resistor 230, a cathode terminal of the diode 216, a first terminal of the resistor 218, an anode terminal of the diode 220, a second terminal of the resistor 206, and a first input terminal of the fully differential amplifier 204.

[0030] Diode circuits 214, 222 of Figure 2 reduce the feedback resistance to fully differential amplifier 204 in response to an input voltage exceeding a first threshold or falling below a second threshold. In Figure 2, diode circuitry 214 includes diodes 216, 220 and resistor 218. Also, diode circuitry 222 includes diodes 224, 228 and resistor 226. However, diode circuitry 214 may be implemented with transistors, as described hereinafter in connection with Figures 5-10.

[0031] 2 has an anode terminal and a cathode terminal. The anode terminal of the diode 216 is coupled to a second terminal of the resistor 218, a cathode terminal of the diode 220, a second terminal of the capacitor 210, a first output terminal of the fully differential amplifier 204, the ADC 108, and a first input of the lossless integrator 202. The cathode terminal of the diode 216 is coupled to a first terminal of the resistor 218, an anode terminal of the diode 220, a first terminal of the capacitor 210, a second terminal of the resistor 206, a first terminal of the resistor 230, and a first input terminal of the fully differential amplifier 204. Diode 216 acts as a resistor with high (e.g., infinite) resistance in response to the output voltage dropping below a threshold voltage (e.g., the turn-on forward voltage of diode 216 and / or the nonlinear compensation voltage of diode 216) and acts as a closed switch with low resistance (also referred to as low impedance) in response to the output voltage exceeding the threshold voltage.

[0032] 2 is a feedback resistor that is selected for particular characteristics, such as bandwidth, gain, center frequency, and / or quality, of the lossy integrator 200. The resistor 218 has two terminals. A first terminal of the resistor 218 is coupled to the cathode terminal of the diode 216, the anode terminal of the diode 220, a first terminal of the capacitor 210, a second terminal of the resistor 206, a first terminal of the resistor 230, and a first terminal of the fully differential amplifier 204. A second terminal of the resistor 218 is coupled to the anode terminal of the diode 216, the cathode terminal of the diode 220, a second terminal of the capacitor 210, a first output terminal of the fully differential amplifier 204, the ADC 108, and a first output of the lossless integrator 202.

[0033] 2 includes an anode terminal and a cathode terminal. The cathode terminal of the diode 220 is coupled to the second terminal of the resistor 218, the anode terminal of the diode 216, the second terminal of the capacitor 210, the first output terminal of the fully differential amplifier 204, the ADC 108, and the first input of the lossless integrator 202. The cathode terminal of the diode 220 is coupled to the first terminal of the resistor 218, the anode terminal of the diode 216, the first terminal of the capacitor 210, the second terminal of the resistor 206, the first terminal of the resistor 230, and the first input terminal of the fully differential amplifier 204. The diode 220 acts as a resistor of high (e.g., infinite) resistance in response to the output voltage dropping below a threshold voltage, e.g., the turn-on or forward voltage of the diode 220. Additionally, diode 220 acts as a low resistance closed switch in response to the output voltage exceeding the threshold voltage.

[0034] 2 includes an anode terminal and a cathode terminal. The anode terminal of the diode 224 is coupled to a second terminal of the resistor 226, a cathode terminal of the diode 228, a second terminal of the capacitor 210, a second output terminal of the fully differential amplifier 204, the ADC 108, and a first input of the lossless integrator 202. The cathode terminal of the diode 224 is coupled to a first terminal of the resistor 226, an anode terminal of the diode 228, a first terminal of the capacitor 210, a second terminal of the resistor 208, a first terminal of the resistor 232, and a second input terminal of the fully differential amplifier 204. The diode 224 operates as a resistor with high (e.g., infinite) resistance in response to the output voltage dropping below a threshold voltage (e.g., the turn-on or forward voltage of the diode 224) and operates as a closed switch with low resistance in response to the output voltage exceeding the threshold voltage.

[0035] 2 is a feedback resistor that is selected for particular characteristics, such as bandwidth, gain, center frequency, and / or quality, of the lossy integrator 200. The resistor 226 has two terminals. A first terminal of the resistor 226 is coupled to the cathode terminal of the diode 224, the anode terminal of the diode 228, the first terminal of the capacitor 210, the second terminal of the resistor 208, the first terminal of the resistor 232, and the second input terminal of the fully differential amplifier 204. A second terminal of the resistor 226 is coupled to the anode terminal of the diode 224, the cathode terminal of the diode 228, the second terminal of the capacitor 210, the second output terminal of the fully differential amplifier 204, the ADC 108, and the first input of the lossless integrator 202.

[0036] 2 has an anode terminal and a cathode terminal. The cathode terminal of diode 228 is coupled to a second terminal of resistor 226, an anode terminal of diode 224, a second terminal of capacitor 210, a second output terminal of fully differential amplifier 204, ADC 108, and a first input of lossless integrator 202. The cathode terminal of diode 228 is coupled to a first terminal of resistor 226, an anode terminal of diode 224, a first terminal of capacitor 210, a second terminal of resistor 208, a first terminal of resistor 232, and a second input terminal of fully differential amplifier 204. Diode 228 operates as a resistor with high (e.g., infinite) resistance in response to the output voltage dropping below a threshold voltage (e.g., the turn-on or forward voltage of diode 228) and operates as a closed switch with low resistance in response to the output voltage exceeding the threshold voltage.

[0037] In operation, in response to the non-inverting input voltage being above a first threshold voltage (e.g., −0.7 volts (V)) and below a second threshold voltage (e.g., 0.7 V), the diodes 216, 220 are off, causing the diodes 216, 220 to operate as open circuits. Thus, the resistance between the first input terminal of the fully differential amplifier 204 and the first output terminal of the fully differential amplifier 204 is a function of the resistance of the resistor 218. In this manner, the gain, the frequency of the unity gain crossover point, and the frequency of the non-dominant pole for the lossy integrator 200 operate based on the resistance of the example resistor 218.

[0038] However, in response to the non-inverting input voltage exceeding the second threshold voltage, the diode 220 turns on, allowing current to flow through the diode 220 and capping the output voltage to prevent the output voltage from exceeding the second threshold voltage. When the diode 220 turns on, the diode 220 has a small amount of resistance (e.g., about 50 ohms). Thus, the resistance between the first input terminal of the fully differential amplifier 204 and the first output terminal of the fully differential amplifier 204 is significantly reduced. For example, the resistance of the diode 220 is now connected in parallel with the resistor 218, thereby lowering the overall feedback resistance. The lowering of the feedback resistance reduces the gain of the fully differential amplifier 204, lowering the frequency of the unity gain crossover point and increasing the frequency of the non-dominant pole. Thus, lowering the feedback resistance increases the frequency between the unity gain crossover point and the non-dominant pole, improving the stability of the bandpass filter 250.

[0039] Also, in response to the non-inverting input voltage being below the first threshold voltage, the diode 216 turns on, allowing current to flow through the diode 216, providing an upper limit to the output voltage to prevent the output voltage from falling below the first threshold voltage. Because the diode 216 has a small amount of resistance (e.g., about 50 ohms), the resistance between the first input terminal of the fully differential amplifier 204 and the first output terminal of the fully differential amplifier 204 is significantly reduced because the resistance of the diode 216 is now in parallel with the resistor 218, thereby reducing the overall feedback resistance. The reduced feedback resistance reduces the gain of the fully differential amplifier 204, lowering the frequency of the unity gain crossover point and increasing the frequency of the non-dominant pole. Thus, reducing the feedback resistance increases the frequency between the unity gain crossover point and the non-dominant pole, improving the stability of the bandpass filter 250. The diode circuit element 222 similarly acts to reduce the gain of the fully differential amplifier 204, moving the frequency between the non-dominant pole and the unity gain crossover point based on the inverting input signal. Also, to obtain symmetry for inverting and non-inverting input signals, the resistance of resistor 226 may be the same as the resistance of resistor 218. However, the resistances of resistors 218, 226 may be any resistance.

[0040] 3 illustrates an example bandpass filter 350 for implementing the example bandpass filter 106 of FIG. 2, comprising a circuit implementation of the lossless integrator 202. The bandpass filter 350 of FIG. 3 includes the example lossy integrator 200 and the example lossless integrator 202 of FIG. 2. The lossy integrator 200 of FIG. 3 includes the example fully differential amplifier 204, example resistors 206, 208, example feedback capacitors 210, 212, example diode circuit elements 214, 222, example diodes 216, 220, 224, 228, and example resistors 218, 226 of FIG. 2. The example bandpass filter 350 of FIG. 3 further includes the feedback resistors 230, 232 of FIG. 2. The example lossless integrator 202 includes example resistors 300 , 302 , an example fully differential amplifier 304 , and example capacitors 306 , 308 .

[0041] 3 of the lossless integrator 202 are input resistors that receive the output of the fully differential amplifier 204. A first terminal of the resistor 300 is coupled to the anode terminal of the diode 216, the second terminal of the resistor 218, the cathode terminal of the diode 220, the second terminal of the capacitor 210, the first output terminal of the fully differential amplifier 204, and the ADC 108. A second terminal of the resistor 300 is coupled to the first terminal of the capacitor 306 and the first input terminal of the fully differential amplifier 304. A first terminal of the resistor 302 is coupled to the anode terminal of the diode 224, the second terminal of the resistor 226, the cathode terminal of the diode 228, the second terminal of the capacitor 212, the second output terminal of the fully differential amplifier 204, and the ADC 108. A second terminal of the resistor 302 is coupled to a first terminal of a capacitor 308 and to a second input terminal of the fully differential amplifier 304. The resistance of the resistors 300, 302 can be selected for a desired gain of the lossless integrator 202.

[0042] The fully differential amplifier 304 of FIG. 3 amplifies the output signal of the fully differential amplifier 204. The output of the fully differential amplifier 304 is fed back to the input of the fully differential amplifier 204 via respective resistors 230, 232. The fully differential amplifier 304 has two input terminals and two output terminals. A first input terminal of the fully differential amplifier 304 is coupled to a second terminal of the resistor 300 and a first terminal of the capacitor 306. A second input terminal of the fully differential amplifier 304 is coupled to a second terminal of the resistor 302 and a first terminal of the capacitor 308. A first output terminal of the fully differential amplifier 304 is coupled to a second terminal of the capacitor 306 and a second terminal of the resistor 230. A second output terminal of the fully differential amplifier 304 is coupled to a second terminal of the capacitor 308 and a second terminal of the resistor 232.

[0043] The capacitors 306, 308 in FIG. 3 are feedback capacitors. The gain of the amplifier 204 is a function of the capacitance of the capacitors 306, 308. A first terminal of the capacitor 306 is coupled to a second terminal of the resistor 300 and to a first input terminal of the fully differential amplifier 304. A second terminal of the capacitor 306 is coupled to a first output terminal of the fully differential amplifier 304 and to a second terminal of the resistor 230. A first terminal of the capacitor 308 is coupled to a second terminal of the resistor 302 and to a second input terminal of the fully differential amplifier 304. A second terminal of the capacitor 308 is coupled to a second output terminal of the fully differential amplifier 304 and to a second terminal of the resistor 232.

[0044] FIG. 4 illustrates an example bandpass filter 450 for implementing the example bandpass filter 106 of FIG. 1 with a “standard” differential amplifier having a differential input and a single-ended output. The bandpass filter 450 of FIG. 4 includes an example lossy integrator 400 and an example lossless integrator 402. The lossy integrator 400 of FIG. 4 includes resistors 206, 218, diode circuit element 214, diodes 216, 220, and capacitor 210 of FIG. 2 and / or FIG. 3. The lossy integrator 400 of FIG. 4 further includes a differential amplifier 404. The lossless integrator 402 of FIG. 4 includes resistor 300 and capacitor 306 of FIG. 3. The lossless integrator 402 further includes an example differential amplifier 406 and an example inverter 408. The bandpass filter 450 of FIG. 4 further includes feedback resistor 230 of FIG. 2 and / or FIG. 3.

[0045] In the example lossy integrator 400 of FIG. 4, the resistors 206, 218, the capacitor 210, the diode circuit element 214, and the diodes 216, 220 operate in the same manner as in FIG. 2 and / or FIG. 3. However, in the lossy integrator 400, the fully differential amplifier 204 is replaced with a differential amplifier 404 (e.g., an op-amp, an error amplifier, etc.), and only one input signal is received. The differential amplifier 404 includes an inverting input terminal, a non-inverting input terminal, and an output terminal. The inverting input terminal of the differential amplifier 404 is coupled to the second terminal of the resistor 206, the first terminal of the resistor 230, the cathode terminal of the diode 216, the first terminal of the resistor 218, the anode terminal of the diode 220, and the first terminal of the capacitor 210. The non-inverting input terminal of the differential amplifier 404 is coupled to ground. The output terminal of the differential amplifier 404 is coupled to the ADC 108, a first input terminal of the lossless integrator 202, an anode terminal of the diode 216, a second terminal of the resistor 218, a cathode terminal of the diode 220, and a second terminal of the capacitor 210.

[0046] In the example lossless integrator 402 of FIG. 4, the resistor 300 and the capacitor 306 operate in the same manner as in FIG. 3. However, in the lossless integrator 402, the fully differential amplifier 304 is replaced with a differential amplifier 406. The differential amplifier 406 includes an inverting input terminal, a non-inverting input terminal, and an output terminal. The inverting input terminal of the differential amplifier 406 is coupled to a second terminal of the resistor 300 and a first terminal of the capacitor 306. The non-inverting input terminal of the differential amplifier 406 is coupled to ground. The output terminal of the differential amplifier 406 is coupled to a second terminal of the capacitor 306 and an input terminal of an inverter 408.

[0047] 4 inverts the output of amplifier 406. Inverter 408 has an input terminal and an output terminal. The input terminal of inverter 408 is coupled to the second terminal of capacitor 306 and to the output terminal of amplifier 406. The output terminal of inverter 408 is coupled to resistor 230.

[0048] Figure 5 illustrates an example bandpass filter 550 for implementing the example bandpass filter 106 of Figure 1. The bandpass filter 550 of Figure 5 includes the example lossy integrator 500 and the example lossless integrator 202 of Figure 2. The lossy integrator 500 of Figure 5 includes the example fully differential amplifier 204, example resistors 206, 208, and example feedback capacitors 210, 212 of Figure 2. The example bandpass filter 550 of Figure 5 further includes the feedback resistors 230, 232 of Figure 2. In FIG. 5, example diode circuit elements 555, 560 replace diodes 216, 220, 224, 228 and resistors 218, 226 of FIGS. 2-4 with example resistors 501, 502, 504, 506, 512, 514, 516, 518 and example transistors 508, 510, 520, 522.

[0049] 5 each have two terminals. A first terminal of resistor 501 is coupled to a first current terminal of transistor 508, a first terminal of resistor 504, a first current terminal of transistor 510, a first terminal of capacitor 210, a first terminal of resistor 230, a second terminal of resistor 206, and a first input terminal of fully differential amplifier 204. A second terminal of resistor 501 is coupled to a first terminal of resistor 502 and a control terminal of transistor 508. A first terminal of resistor 502 is coupled to a second terminal of resistor 501 and a control terminal of transistor 508. A second terminal of the resistor 502 is coupled to a second current terminal of the transistor 508, a second terminal of the resistor 506, a second current terminal of the transistor 510, a second terminal of the capacitor 210, a first output terminal of the fully differential amplifier 204, the ADC 108, and a first input terminal of the lossless integrator 202. A first terminal of the resistor 504 is coupled to a first current terminal of the transistor 508, a first terminal of the resistor 501, a first current terminal of the transistor 510, a first terminal of the capacitor 210, a first terminal of the resistor 230, a second terminal of the resistor 206, and a first input terminal of the fully differential amplifier 204. A second terminal of the resistor 504 is coupled to a first terminal of the resistor 506 and a control terminal of the transistor 510. A first terminal of the resistor 502 is coupled to a second terminal of the resistor 504 and a control terminal of the transistor 510. The second terminal of the resistor 502 is coupled to a second current terminal of the transistor 508, a second terminal of the resistor 502, a second current terminal of the transistor 510, a second terminal of the capacitor 210, a first output terminal of the fully differential amplifier 204, the ADC 108, and a first input terminal of the lossless integrator 202.

[0050] The transistors 508, 510 in FIG. 5 are bipolar junction transistors (BJTs). However, the transistors 508, 510 may be metal oxide semiconductor field effect transistors (MOSFETs) and / or any other type of transistors. The transistors 508, 510 each have two "current" terminals (e.g., an emitter terminal and a collector terminal) and a control terminal (e.g., a base terminal). A first current terminal of the transistor 508 is coupled to a terminal of the resistor 501, a first terminal of the resistor 504, a first current terminal of the transistor 510, a first terminal of the capacitor 210, a first terminal of the resistor 230, a second terminal of the resistor 206, and a first input terminal of the fully differential amplifier 204. A second current terminal of transistor 508 is coupled to the second terminal of resistor 502, the second terminal of resistor 506, a second current terminal of transistor 510, a second terminal of capacitor 210, a first output terminal of fully differential amplifier 204, ADC 108, and a first input terminal of lossless integrator 202. A control terminal of transistor 508 is coupled to the second terminal of resistor 501 and a first terminal of resistor 502. A first current terminal of transistor 510 is coupled to a terminal of resistor 501, a first terminal of resistor 504, a first current terminal of transistor 508, a first terminal of capacitor 210, a first terminal of resistor 230, a second terminal of resistor 206, and a first input terminal of fully differential amplifier 204. A second current terminal of transistor 510 is coupled to the second terminal of resistor 502, the second terminal of resistor 506, a second current terminal of transistor 508, a second terminal of capacitor 210, a first output terminal of fully differential amplifier 204, ADC 108, and a first input terminal of lossless integrator 202. A control terminal of transistor 510 is coupled to the second terminal of resistor 504 and to the first terminal of resistor 506.

[0051] 5 each have two terminals. A first terminal of resistor 512 is coupled to a first current terminal of transistor 520, a first terminal of resistor 516, a first current terminal of transistor 522, a first terminal of capacitor 212, a first terminal of resistor 232, a second terminal of resistor 208, and a second input terminal of fully differential amplifier 204. A second terminal of resistor 512 is coupled to a first terminal of resistor 514 and to a control terminal of transistor 520. A first terminal of resistor 514 is coupled to a second terminal of resistor 512 and to a control terminal of transistor 520. A second terminal of the resistor 514 is coupled to a second current terminal of the transistor 520, a second terminal of the resistor 518, a second current terminal of the transistor 522, a second terminal of the capacitor 212, a second output terminal of the fully differential amplifier 204, the ADC 108, and a second input terminal of the lossless integrator 202. A first terminal of the resistor 516 is coupled to a first current terminal of the transistor 520, a first terminal of the resistor 512, a first current terminal of the transistor 522, a first terminal of the capacitor 212, a first terminal of the resistor 232, a second terminal of the resistor 208, and a second input terminal of the fully differential amplifier 204. A second terminal of the resistor 516 is coupled to a first terminal of the resistor 518 and a control terminal of the transistor 522. A first terminal of the resistor 514 is coupled to a second terminal of the resistor 516 and a control terminal of the transistor 522. The second terminal of resistor 514 is coupled to a second current terminal of transistor 520, a second terminal of resistor 514, a second current terminal of transistor 522, a second terminal of capacitor 212, a second output terminal of fully differential amplifier 204, ADC 108, and a second input terminal of lossless integrator 202.

[0052] The transistors 520, 522 in FIG. 5 are bipolar junction transistors (BJTs). However, the transistors 520, 522 may be metal oxide semiconductor field effect transistors (MOSFETs) and / or any other type of transistors. The transistors 520, 522 each have two current terminals (e.g., an emitter terminal and a collector terminal) and a control terminal (e.g., a base terminal). A first current terminal of the transistor 520 is coupled to a terminal of the resistor 512, a first terminal of the resistor 516, a first current terminal of the transistor 522, a first terminal of the capacitor 212, a first terminal of the resistor 232, a second terminal of the resistor 208, and a second input terminal of the fully differential amplifier 204. A second current terminal of the transistor 520 is coupled to a second terminal of the resistor 514, a second terminal of the resistor 518, a second current terminal of the transistor 522, a second terminal of the capacitor 212, a second output terminal of the fully differential amplifier 204, the ADC 108, and a second input terminal of the lossless integrator 202. A control terminal of the transistor 520 is coupled to a second terminal of the resistor 512 and a first terminal of the resistor 514. A first current terminal of the transistor 522 is coupled to a terminal of the resistor 512, a first terminal of the resistor 516, a first current terminal of the transistor 508, a first terminal of the capacitor 212, a first terminal of the resistor 232, a second terminal of the resistor 208, and a second input terminal of the fully differential amplifier 204. A second current terminal of transistor 522 is coupled to the second terminal of resistor 514, the second terminal of resistor 518, a second current terminal of transistor 520, a second terminal of capacitor 212, a second output terminal of fully differential amplifier 204, ADC 108, and a second input terminal of lossless integrator 202. A control terminal of transistor 522 is coupled to the second terminal of resistor 516 and to the first terminal of resistor 518.

[0053] As previously described, the diode circuit elements 214, 222 include diodes 216, 220, 224, 228. The diodes 216, 228 turn on (e.g., to operate as low impedance short circuits) in response to the input voltage exceeding a first threshold (e.g., 0.7V). And, the diodes 220, 224 turn on in response to the input voltage dropping below a second threshold (e.g., −0.7V). The thresholds are based on the diode characteristics. The example diode circuit elements 555, 560 of FIG. 5 operate similarly to the diode circuit elements of FIGS. 2-4, except that the threshold voltages at which the transistors turn on and operate like diodes can be controlled based on, e.g., as a function of, selected resistor values ​​501, 502, 504, 506. For example, transistor 508 acts like a diode when the turn-on voltage is based on resistors 501, 502, e.g., a function of resistors 501, 502. That is, the turn-on voltage is (1+r1 / r2)×vbe, where r1 is the resistance of resistor 501, r2 is the resistance of resistor 502, and vbe is the base-emitter voltage of transistor 508.

[0054] In this manner, a user and / or manufacturer can adjust the turn-on voltages for transistors 508, 510, 520, 522 to cap the input signal to a maximum and / or minimum value based on the particular resistances selected for the corresponding resistors 501, 502, 504, 506, 512, 514, 516, 518. Additionally, the resistances of 501, 502, 504, 506 can be selected such that the total feedback resistance is equal to the resistance of resistor 218, for example, to obtain a desired quality value. Similarly, resistors 512, 514, 516, 518 can be selected to control the turn-on voltages of respective transistors 520, 522 such that the total feedback resistance is equal to the resistance of resistor 226, for example, to obtain a desired quality value. Also, to obtain symmetry for inverting and non-inverting input signals, the resistance of resistor 512 may be the same as the resistance of resistor 501, the resistance of resistor 514 may be the same as the resistance of resistor 502, the resistance of resistor 516 may be the same as the resistance of resistor 504, and the resistance of resistor 518 may be the same as the resistance of resistor 506. However, the resistances of resistors 501, 502, 504, 506, 512, 516, 518 may be any resistance.

[0055] 6 illustrates an example bandpass filter 650 for implementing the example bandpass filter 106 of FIG. 5, comprising a circuit implementation of the lossless integrator 202. The bandpass filter 650 of FIG. 6 includes the example lossy integrator 500 and the example lossless integrator 202 of FIG. 2. The lossy integrator 500 of FIG. 6 includes the example fully differential amplifier 204, the example resistors 206, 208, and the example feedback capacitors 210, 212 of FIG. 2. The lossy integrator 500 further includes resistors 501, 502, 504, 506, 512, 514, 516, 518 of FIG. 5, transistors 508, 510, 520, 522, and example diode circuit elements 555, 560. The example bandpass filter 650 of FIG. 6 further includes feedback resistors 230, 232 of FIG. 2. The example lossless integrator 202 includes example resistors 300 , 302 , an example fully differential amplifier 304 , and example capacitors 306 , 308 .

[0056] FIG. 7 illustrates an example bandpass filter 750 for implementing the example bandpass filter 106 of FIG. 1 with a differential amplifier. The bandpass filter 750 of FIG. 7 includes an example lossy integrator 700 and an example lossless integrator 702. The lossy integrator 700 of FIG. 7 includes resistors 206, 501, 502, 504, 506 and transistors 508, 510 of FIG. 5 and / or FIG. 6. The lossy integrator 700 of FIG. 7 further includes the differential amplifier 404 of FIG. 4. The lossless integrator 702 of FIG. 7 includes resistor 300 and capacitor 306 of FIG. 3. The lossless integrator 702 further includes the differential amplifier 406 and inverter 408 of FIG. 4. The bandpass filter 750 of FIG. 7 further includes the feedback resistor 230 of FIG. 2-FIG. 6.

[0057] In the example lossy integrator 700 of FIG. 7, resistors 206, 501, 502, 504, 506, capacitor 210, diode circuit element 555, and transistors 508, 510 operate similarly to those in FIG. 5 and / or FIG. 6. However, in the lossy integrator 700, the fully differential amplifier 204 is replaced with a differential amplifier 404 (e.g., an op-amp, an error amplifier, etc.) of FIG. 4, and only one input signal is received. The differential amplifier 404 has an inverting input terminal, a non-inverting input terminal, and an output terminal. The inverting input terminal of the differential amplifier 404 is coupled to a second terminal of the resistor 206, a first terminal of the resistor 230, a first current terminal of the transistor 508, a first terminal of the resistor 501, a first terminal of the resistor 504, a first current terminal of the transistor 510, and a first terminal of the capacitor 210. A non-inverting input terminal of the differential amplifier 404 is coupled to ground. An output terminal of the differential amplifier 404 is coupled to the ADC 108, a first input terminal of the lossless integrator 202, a second current terminal of the transistor 508, a second terminal of the resistor 502, a second terminal of the resistor 506, a second current terminal of the transistor 510, and a second terminal of the capacitor 210.

[0058] In the example lossless integrator 702 of FIG. 7, the resistor 300 and the capacitor 306 operate similarly to those in FIG. 3 and / or FIG. 6. However, in the lossless integrator 702, the fully differential amplifier 304 is replaced with a differential amplifier 406. The differential amplifier 406 has an inverting input terminal, a non-inverting input terminal, and an output terminal. The inverting input terminal of the differential amplifier 406 is coupled to a second terminal of the resistor 300 and to a first terminal of the capacitor 306. The non-inverting input terminal of the differential amplifier 406 is coupled to ground. The output terminal of the differential amplifier 406 is coupled to a second terminal of the capacitor 306 and to a second terminal of the input terminal of the inverter 408.

[0059] Figure 8 illustrates an example bandpass filter 850 for implementing the example bandpass filter 106 of Figure 1. The bandpass filter 106 of Figure 8 includes an example lossy integrator 800 and the example lossless integrator 202 of Figure 2. The lossy integrator 800 of Figure 8 includes the example fully differential amplifier 204, example resistors 206, 208, and example feedback capacitors 210, 212 of Figure 2. The example bandpass filter 850 further includes feedback resistors 230, 232 of Figure 2. In FIG. 8, example diode circuit elements 855, 860 replace diodes 216, 220, 224, 228 and resistors 218, 226 of FIGS. 2-4 and / or example resistors 501, 502, 504, 506, 512, 514, 516, 518 and transistors 508, 510, 520, 522 of FIGS. 5-7 with example resistors 801, 802, 804, 810, 812, 814 and example transistors 806, 808, 816, 818.

[0060] Resistors 801, 802, and 804 in FIG. 8 each have two terminals. A first terminal of resistor 801 is coupled to a first current terminal of transistor 806, a first current terminal of transistor 808, a first terminal of capacitor 210, a first terminal of resistor 230, a second terminal of resistor 206, and a first input terminal of fully differential amplifier 204. A second terminal of resistor 801 is coupled to a first terminal of resistor 802 and a control terminal of transistor 806. A first terminal of resistor 802 is coupled to a second terminal of resistor 801 and a control terminal of transistor 806. A second terminal of resistor 802 is coupled to a first terminal of resistor 804 and a control terminal of transistor 808. A first terminal of resistor 804 is coupled to a second terminal of resistor 802 and a current terminal of transistor 808. The second terminal of resistor 804 is coupled to a second current terminal of resistor 806, a second current terminal of transistor 808, a second terminal of capacitor 210, a first output terminal of fully differential amplifier 204, ADC 108, and a first input terminal of lossless integrator 202.

[0061] The transistors 806, 808 in FIG. 8 are bipolar junction transistors (BJTs). However, the transistors 806, 808 may be metal oxide semiconductor field effect transistors (MOSFETs) and / or any other type of transistors. The transistors 806, 808 each have two current terminals (e.g., an emitter terminal and a collector terminal) and a control terminal (e.g., a base terminal). A first current terminal of the transistor 806 is coupled to a first terminal of the resistor 801, a first current terminal of the transistor 808, a first terminal of the capacitor 210, a first terminal of the resistor 230, a second terminal of the resistor 206, and a first input terminal of the fully differential amplifier 204. A second current terminal of transistor 806 is coupled to a second terminal of resistor 804, a second current terminal of transistor 808, a second terminal of capacitor 210, a first output terminal of fully differential amplifier 204, ADC 108, and a first input terminal of lossless integrator 202. A control terminal of transistor 806 is coupled to a second terminal of resistor 801 and a first terminal of resistor 802. A first current terminal of transistor 808 is coupled to a terminal of resistor 801, a first current terminal of transistor 806, a first terminal of capacitor 210, a first terminal of resistor 230, a second terminal of resistor 206, and a first input terminal of fully differential amplifier 204. A second current terminal of transistor 808 is coupled to the second terminal of resistor 804, to the second current terminal of transistor 806, to a second terminal of capacitor 210, to a first output terminal of fully differential amplifier 204, to ADC 108, and to a first input terminal of lossless integrator 202. A control terminal of transistor 808 is coupled to the second terminal of resistor 804 and to the first terminal of resistor 802.

[0062] The resistors 810, 812, and 814 in FIG. 8 each have two terminals. A first terminal of the resistor 810 is coupled to a first current terminal of the transistor 816, a first current terminal of the transistor 818, a first terminal of the capacitor 212, a first terminal of the resistor 232, a second terminal of the resistor 208, and a second input terminal of the fully differential amplifier 204. A second terminal of the resistor 810 is coupled to a first terminal of the resistor 812 and a control terminal of the transistor 816. A first terminal of the resistor 812 is coupled to a second terminal of the resistor 810 and a control terminal of the transistor 816. A second terminal of the resistor 812 is coupled to a first terminal of the resistor 814 and a control terminal of the transistor 818. A first terminal of the resistor 814 is coupled to a second terminal of the resistor 812 and a control terminal of the transistor 818. A second terminal of resistor 814 is coupled to a second current terminal of transistor 816, a second current terminal of transistor 818, a second terminal of capacitor 212, a second output terminal of fully differential amplifier 204, ADC 108, and a second input terminal of lossless integrator 202.

[0063] The transistors 816, 818 in FIG. 8 are bipolar junction transistors (BJTs). However, the transistors 816, 818 may be metal oxide semiconductor field effect transistors (MOSFETs) and / or any other type of transistors. The transistors 816, 818 each have two current terminals (e.g., an emitter terminal and a collector terminal) and a control terminal (e.g., a base terminal). A first current terminal of the transistor 816 is coupled to a terminal of the resistor 810, a first current terminal of the transistor 818, a first terminal of the capacitor 212, a first terminal of the resistor 232, a second terminal of the resistor 208, and a second input terminal of the fully differential amplifier 204. A second current terminal of the transistor 816 is coupled to a second terminal of the resistor 814, a second current terminal of the transistor 818, a second terminal of the capacitor 212, a second output terminal of the fully differential amplifier 204, the ADC 108, and a second input terminal of the lossless integrator 202. A control terminal of the transistor 816 is coupled to a second terminal of the resistor 810 and a first terminal of the resistor 812. A first current terminal of the transistor 818 is coupled to a terminal of the resistor 810, a first current terminal of the transistor 816, a first terminal of the capacitor 212, a first terminal of the resistor 232, a second terminal of the resistor 208, and a second input terminal of the fully differential amplifier 204. A second current terminal of transistor 818 is coupled to the second terminal of resistor 814, to a second current terminal of transistor 816, to a second terminal of capacitor 212, to a second output terminal of fully differential amplifier 204, to ADC 108, and to a second input terminal of lossless integrator 202. A control terminal of transistor 818 is coupled to the second terminal of resistor 814 and to the first terminal of resistor 812.

[0064] As previously described, the diode circuit elements 214, 222 include the diodes 216, 220, 224, 228 of FIGS. 2-4 that turn on (e.g., to operate as a low impedance short circuit) in response to the input voltage exceeding a first threshold (e.g., 0.7V) or falling below a second threshold (e.g., −0.7V). The thresholds are based on the diode characteristics. As described in FIGS. 5-7, the resistors 501, 502, 504, 506, 512, 514, 516, 518 and the transistors 508, 510, 520, 522 operate in a similar manner to the diode circuit elements 214, 222 of FIGS. 2-4, where the turn-on voltages can be selected based on the resistance values ​​of the resistors 501, 502, 504, 506, 512, 514, 516, 518. The example diode circuit elements 855, 860 of Figure 8 operate in the same manner as the diode circuit elements 555, 560 of Figures 5-7. However, the diode circuit elements 855, 860 include one less transistor. Thus, the transistor 806 operates like a diode whose turn-on voltage is based on the resistors 801, 802, 804. For example, the turn-on voltage is (1+r1 / (r3+r2)×vbe, where r1 is the resistance of resistor 801, r2 is the resistance of resistor 802, r3 is the resistance of resistor 804, and vbe is the base-emitter voltage of transistor 806. Transistor 808 also acts like a diode whose turn-on voltage is based on resistors 801, 802, and 804. For example, the turn-on voltage is (1+r3 / (r1+r2)×vbe, where r1 is the resistance of resistor 801, r2 is the resistance of resistor 802, r3 is the resistance of resistor 804, and vbe is the base-emitter voltage of transistor 806.

[0065] In this manner, a user and / or manufacturer can adjust the turn-on voltage to limit the input signal to a maximum and / or minimum value based on the particular resistances selected for resistors 801, 802, 804, 810, 812, 814. In the example of FIG. 8, the resistance of resistor 801 and the resistance of resistor 804 are the same in symmetry, e.g., the turn-on voltage of transistor 806 is opposite to the turn-on voltage of transistor 808. However, the resistance of resistors 801, 802, 804 may be selected to be any resistance. Also, the resistance of 801, 802, 804 may be selected such that the total feedback resistance is equal to the resistance of resistor 218. For example, the sum of the resistances of resistors 801, 802, 804 is equal to the resistance of resistor 218 of FIG. 2 to obtain a desired quality value. Similarly, resistors 810, 812, 814 may be selected to control the turn-on voltages of respective transistors 816, 818 such that the total feedback resistance is equal to the resistance of resistor 226, for example, to obtain a desired quality value. Also, to obtain symmetry for inverting and non-inverting input signals, the resistance of resistor 810 may be the same as the resistance of resistor 801, the resistance of resistor 812 may be the same as the resistance of resistor 802, and the resistance of resistor 814 may be the same as the resistance of resistor 804. However, the resistances of resistors 801, 802, 804, 810, 812, 814 may be any resistance.

[0066] 9 illustrates an example bandpass filter 950 for implementing the example bandpass filter 106 of FIG. 8, comprising a circuit implementation of the lossless integrator 202. The bandpass filter 950 of FIG. 9 includes the example lossy integrator 800 of FIG. 8 and the example lossless integrator 202 of FIG. 2. The lossy integrator 800 of FIG. 9 includes the example fully differential amplifier 204, the example resistors 206, 208, and the example feedback capacitors 210, 212 of FIG. 2. The lossy integrator 800 further includes resistors 801, 802, 804, 810, 812, 814 of FIG. 8, transistors 806, 808, 816, 818, and example diode circuit elements 855, 860. The example bandpass filter 950 of FIG. 9 further includes feedback resistors 230, 232 of FIG. 2. The example lossless integrator 202 includes example resistors 300 , 302 , an example fully differential amplifier 304 , and example capacitors 306 , 308 .

[0067] FIG. 10 illustrates an example bandpass filter 1050 for implementing the example bandpass filter 106 of FIG. 1 with a differential amplifier. The bandpass filter 1050 of FIG. 10 includes an example lossy integrator 1000 and an example lossless integrator 1002. The lossy integrator 1000 of FIG. 10 includes resistors 206, 801, 802, 804 and transistors 806, 808 of FIG. 8 and / or FIG. 9. The lossy integrator 1000 of FIG. 10 further includes the differential amplifier 404 of FIG. 4. The lossless integrator 1002 of FIG. 10 includes resistor 300 and capacitor 306 of FIG. 3. The lossless integrator 1002 further includes the differential amplifier 406 and inverter 408 of FIG. 4. The bandpass filter 1050 of FIG. 10 further includes the feedback resistor 230 of FIG. 2-FIG. 9.

[0068] In the example lossy integrator 1000 of FIG. 10, resistors 206, 801, 802, 804, capacitor 210, diode circuit element 855, and transistors 806, 808 operate similarly to those in FIG. 8 and / or FIG. 9. However, in the lossy integrator 1000, the fully differential amplifier 204 is replaced with a differential amplifier 404 (e.g., an op-amp, an error amplifier, etc.) of FIG. 4, and only one input signal is received. The differential amplifier 404 includes an inverting input terminal, a non-inverting input terminal, and an output terminal. The inverting input terminal of the differential amplifier 404 is coupled to the second terminal of the resistor 206, the first terminal of the resistor 230, the first current terminal of the transistor 806, the first terminal of the resistor 801, the first current terminal of the transistor 808, and the first terminal of the capacitor 210. The non-inverting input terminal of the differential amplifier 404 is coupled to ground. The output terminal of the differential amplifier 404 is coupled to the ADC 108, a first input terminal of the lossless integrator 202, a second current terminal of the transistor 806, a second terminal of the resistor 804, a second current terminal of the transistor 808, and a second terminal of the capacitor 210.

[0069] In the example lossless integrator 1002 of FIG. 10, the resistor 300 and the capacitor 306 operate in the same manner as in FIG. 3, FIG. 6, and / or FIG. 9. However, in the lossless integrator 1002, the fully differential amplifier 304 is replaced with a differential amplifier 406. The differential amplifier 406 includes an inverting input terminal, a non-inverting input terminal, and an output terminal. The inverting input terminal of the differential amplifier 406 is coupled to a second terminal of the resistor 300 and a first terminal of the capacitor 306. The non-inverting input terminal of the differential amplifier 406 is coupled to ground. The output terminal of the differential amplifier 406 is coupled to a second terminal of the capacitor 306 and an input terminal of an inverter 408.

[0070] Figure 11 is a flow chart depicting a method and / or example operations 1100 that may be performed by the circuit elements of bandpass filters 106, 250, 350, 450, 550, 650, 750, 850, 950, 1050 of Figures 1, 2, 3, 4, 5, 6, 7, 8, 9, and / or 10. Although the operations of Figure 11 are described with reference to bandpass filter 106 in image scanning machine 100 of Figure 1, such operations may also be described with reference to any of bandpass filters 250, 350, 450, 550, 650, 750, 850, 950, 1050 of Figures 2-10, stand-alone bandpass filters, and / or bandpass filters included in any type of circuit element, device, and / or system.

[0071] The operation 1100 of FIG. 11 begins at block 1102, where a diode circuit element 214, 222, 555, 560, 855, 860 of any of FIGS. 2-10 is used to determine if the input voltage is above a first threshold. As previously described, the first threshold corresponds to a turn-on voltage and may be based on the characteristics of the diode 220, 228 and / or the resistance of the resistor 501, 502, 512, 514, 801, 802, 804, 810, 812, 814. If the input voltage is above the first threshold voltage (block 1102: yes), the diode circuit element 214, 222, 555, 560, 855, 860 applies a low feedback resistance to move the non-dominant pole to a higher frequency and / or move the unity gain crossover point to a lower frequency (block 1104). For example, the diodes 220, 228 and / or the transistors 508, 520 turn on and act as low impedance short circuits. In response to the diodes 220, 228 and / or the transistors 508, 520 turning on, the resistance of the low impedance path is in parallel with the resistance of the resistors 218, 226, 501, 502, 504, 506, 512, 514, 516, 518, 801, 802, 804, 810, 812, 814, thereby reducing the feedback resistance. As discussed above, reducing the feedback resistance reduces the gain of the lossy amplifier 200, 400, 500, 700, 800, 1000, moves the non-dominant pole to a higher frequency, and / or moves the unity gain crossover point to a lower frequency. Shifting the frequency of the non-dominant pole and the unity gain crossover point improves the stability of the bandpass filter 106.

[0072] If the input voltage does not exceed the first threshold voltage (block 1102: No), the diode circuit element 214, 222, 555, 560, 855, 860 applies a high feedback resistance corresponding to the resistance of the resistor 218, 226, 501, 502, 504, 506, 512, 514, 516, 518, 801, 802, 804, 810, 812, 814 (block 1106).

[0073] In block 1106, the diode circuit element 214, 222, 555, 560, 855, 860 of any of Figures 2-10 is used to determine if the input voltage is below a second threshold. As previously described, the second threshold corresponds to a turn-on voltage and may be based on the characteristics of the diode 216, 224 and / or the resistance of the resistor 504, 506, 516, 518, 801, 802, 804, 810, 812, 814. If the input voltage is below the second threshold (block 1106: Yes), the diode circuit element 214, 222, 555, 560, 855, 860 applies a low feedback resistance to move the non-dominant pole to a higher frequency and / or move the unity gain crossover point to a lower frequency (block 1108). For example, the diodes 216, 224 and / or the transistors 510, 522 are turned on and act as low impedance short circuits. In response to the diodes 216, 224 and / or the transistors 510, 522 being turned on, the resistance of the low impedance path is in parallel with the resistance of the resistors 218, 226, 501, 502, 504, 506, 512, 514, 516, 518, 801, 802, 804, 810, 812, 814, thereby reducing the feedback resistance. As described above, reducing the feedback resistance reduces the gain of the lossy amplifier 200, 400, 500, 700, 800, 1000, moves the non-dominant pole to a higher frequency, and / or moves the unity gain crossover point to a lower frequency. Shifting the frequency of the non-dominant pole and the unity gain crossover point improves the stability of the bandpass filter 106. After block 1108, control returns to block 1102.

[0074] If the input voltage is not below the second threshold voltage (block 1108: NO), the diode circuit element 214, 222, 555, 560, 855, 860 applies a high feedback resistance (block 1112) corresponding to the resistance of the resistor 218, 226, 501, 502, 504, 506, 512, 514, 516, 518, 801, 802, 804, 810, 812, 814. After block 1112, control returns to block 1102.

[0075] FIG. 12 is an example timing diagram 1200 illustrating an example overload input signal 1202, an example bandpass filter output 1204 without the diode circuit elements 214, 222, 555, 560, 855, 860 of FIGS. 2-10, and an example bandpass filter output 1206 with the diode circuit elements 214, 222, 555, 560, 855, 860 of FIGS. 2-10.

[0076] The example overload input signal 1202 starts with a signal four times the amplitude expected from the output of the front-end amplification state circuitry 104. The overload input signal 1202 then decreases to a manageable amplitude. As shown in the example bandpass filter output 1204, the output signal swings due to the overload input signal 1202 and does not recover after the overload input signal 1202 drops to a manageable amplitude. Therefore, a bandpass filter without the diode circuitry 214, 222, 555, 560, 855, 860 is an unstable system in response to the overload input signal 1202 being applied to the corresponding bandpass filter. As shown in the example bandpass filter output 1206, the output signal swings with the overload input signal 1202 and recovers after the overload input signal 1202 drops to a manageable amplitude. Therefore, the bandpass filter 106 described herein, including diode circuit elements 214, 222, 555, 560, 855, 860, is a stable system that responds to an overloaded input signal 1202 being applied.

[0077] An example manner of implementing the bandpass filter 106 of Figure 1 is illustrated in Figure 2. However, one or more of the elements, processes, and / or devices illustrated in Figures 2-10 may be combined, divided, rearranged, omitted, eliminated, and / or implemented in any other manner.

[0078] Also, the components of Figures 2-10 may include one or more elements, processes, and / or devices in addition to or instead of those illustrated in Figures 2-10, and / or may include two or more of any or all of the illustrated elements, processes, and devices. As used herein, the phrase "in communication," including variations thereof, encompasses direct communication and / or indirect communication through one or more intermediate components, and does not necessarily require direct physical (e.g., wired) communication and / or constant communication, but rather includes selective communication at periodic intervals, scheduled intervals, aperiodic intervals, and / or one-time events.

[0079] Also, although example operations are described with reference to the flowchart shown in Figure 11, many other ways of implementing the bandpass filters 106, 250, 350, 450, 550, 650, 750, 850, 950, 1050 may alternatively be used. For example, the order of the blocks may be changed and / or some of the described blocks may be changed, eliminated, or combined.

[0080] Descriptors such as "first," "second," and "third" are used herein to identify multiple elements or components that may be referenced individually. Unless otherwise specified or understood based on the context in which they are used, such descriptors do not imply any sense of priority, physical order, or placement in a list, or ordering in time, but are used merely as labels to refer to multiple elements or components individually to facilitate understanding of the examples being described. In some instances, the descriptor "first" may be used to refer to an element in the Detailed Description, but the same element may be referred to in the claims using a different descriptor, such as "second" or "third." In such cases, it is to be understood that such descriptors are used merely to facilitate reference to multiple elements or components.

[0081] In this description and in the claims, the terms "comprise" and "have," and variations thereof, are intended to be inclusive in a manner similar to the term "including." Unless otherwise stated, "about," "approximately," or "substantially" preceding a value means within ±10 percent of the stated value. In another example, "about," "approximately," or "substantially" preceding a value means within ±5 percent of the stated value. In another example, "about," "approximately," or "substantially" preceding a value means within ±1 percent of the stated value.

[0082] The terms "couple," "coupled," "couples," and variations thereof, as used herein, may cover connections, communications, or signal paths that enable a functional relationship consistent with this description. For example, in a first example, device A is coupled to device B if device A generates a signal to control device B to perform an action, or in a second example, device A is coupled to device B via an intervening component C such that device B is controlled by device A via a control signal generated by device A, where intervening component C does not substantially change the functional relationship between device A and device B. Additionally, the terms "couple," "coupled," "couples," and variations thereof include indirect or direct electrical or mechanical connections.

[0083] A device that is "configured to" perform a certain task or function may be configured (e.g., programmed and / or hardwired) at the time of manufacture by a manufacturer to perform that function and / or may be configurable (or reconfigurable) by a user after manufacture to perform that function and / or other additional or alternative functions. Such configuration may occur through firmware and / or software programming of the device, through the construction and / or layout of the hardware components and interconnections of the device, or a combination thereof.

[0084] Although not all are individually labeled in the drawings, the components or elements of the systems and circuits shown in the drawings have one or more conductors or terminations that allow signals into and / or out of the component or element. A conductor or termination (or portions thereof) may be referred to herein as a pin, pad, terminal (including, for example, input terminal, output terminal, reference terminal, and ground terminal), input, output, node, and interconnect.

[0085] As used herein, a "terminal" of a component, device, system, circuit, integrated circuit, or other electronic or semiconductor component generally refers to a conductor, such as a wire, trace, pin, pad, or other connector or interconnect, that allows the component, device, system, etc. to be electrically and / or mechanically connected to another component, device, system, etc. A terminal may be used, for example, to receive or provide an analog or digital electrical signal (or simply a signal), or to electrically connect to a common or ground reference. Thus, an input terminal or input is used to receive a signal from another component, device, system, etc. An output terminal or output is used to provide a signal to another component, device, system, etc. Other terminals may be used to connect to a common, ground, or voltage reference, e.g., a reference terminal or ground terminal. A terminal of an IC or PCB may also be referred to as a pin (a long conductor) or a pad (a flat conductor). A node refers to a point of connection or interconnection of two or more terminals. An example number of terminals and nodes may be shown. However, there may be more or fewer terminals or nodes depending on the particular circuit or system topology. However, in some cases, "terminal," "node," "interconnect," "pad," and "pin" may be used interchangeably.

[0086] Modifications in the described embodiments are possible, and other embodiments are possible, within the scope of the appended claims.

Claims

1. 1. A circuit comprising: an amplifier having an input terminal and an output terminal; a capacitor having a first terminal and a second terminal, the first terminal of the capacitor being coupled to the input terminal of the amplifier and the second terminal of the capacitor being coupled to the output terminal of the amplifier; a diode circuit element having a first terminal and a second terminal; Including, the first terminal of the diode circuit element is coupled to the first terminal of the capacitor and to the input terminal of the amplifier, and the second terminal of the diode circuit element is coupled to the second terminal of the capacitor and to the output terminal of the amplifier. circuit.

2. 2. The circuit of claim 1, wherein the diode circuit element comprises: a resistor having a first terminal and a second terminal, the first terminal of the resistor being coupled to the input terminal of the amplifier and to the first terminal of the capacitor, and the second terminal of the resistor being coupled to the output terminal of the amplifier and to the second terminal of the capacitor; a first diode having an anode terminal and a cathode terminal, the anode terminal of the first diode being coupled to the first terminal of the resistor, the first terminal of the capacitor, and the input terminal of the amplifier, and the cathode terminal of the first diode being coupled to the second terminal of the resistor, the second terminal of the capacitor, and the output terminal of the amplifier; a second diode having an anode terminal and a cathode terminal, the cathode terminal of the second diode being coupled to the first terminal of the resistor, the first terminal of the capacitor, and the input terminal of the amplifier, and the anode terminal of the second diode being coupled to the second terminal of the resistor, the second terminal of the capacitor, and the output terminal of the amplifier; The circuit includes:

3. 2. The circuit of claim 1, wherein the diode circuit element comprises: a first resistor having a first terminal and a second terminal, the first terminal of the first resistor being coupled to the first terminal of the capacitor and to the input terminal of the amplifier; a second resistor having a first terminal and a second terminal, the first terminal of the second resistor being coupled to the second terminal of the first resistor and the second terminal of the second resistor being coupled to the second terminal of the capacitor and to the output terminal of the amplifier; a transistor having a first current terminal, a second current terminal and a control terminal, the first current terminal of the transistor being coupled to the first terminal of the first resistor, the first terminal of the capacitor and the input terminal of the amplifier, the second current terminal of the transistor being coupled to the second terminal of the second resistor, the second terminal of the capacitor and the output terminal of the amplifier, and the control terminal of the transistor being coupled to the second terminal of the first resistor and the first terminal of the second resistor; The circuit includes:

4. 4. The circuit of claim 3, wherein the transistor is a first transistor and the diode circuit element comprises: a third resistor having a first terminal and a second terminal, the first terminal of the third resistor being coupled to the first terminal of the capacitor, the input terminal of the amplifier, the first terminal of the first resistor, and the first current terminal of the first transistor; a fourth resistor having a first terminal and a second terminal, the first terminal of the fourth resistor being coupled to the second terminal of the third resistor, and the second terminal of the fourth resistor being coupled to the second terminal of the capacitor, the output terminal of the amplifier, the second terminal of the second resistor, and the second current terminal of the first transistor; a second transistor having a first current terminal, a second current terminal and a control terminal, the first current terminal of the second transistor being coupled to the first terminal of the first resistor, the first terminal of the third resistor, the first current terminal of the first transistor, the first terminal of the capacitor, and the input terminal of the amplifier, the second current terminal of the second transistor being coupled to the second terminal of the second resistor, the second terminal of the fourth resistor, the second current terminal of the first transistor, the second terminal of the capacitor, and the output terminal of the amplifier, and the control terminal of the second transistor being coupled to the second terminal of the third resistor and the first terminal of the fourth resistor; The circuit further comprises:

5. 2. The circuit of claim 1, wherein the diode circuit element comprises: a first resistor having a first terminal and a second terminal, the first terminal of the first resistor being coupled to the first terminal of the capacitor and to the input terminal of the amplifier; a second resistor having a first terminal and a second terminal, the first terminal of the second resistor being coupled to the second terminal of the first resistor; a third resistor having a first terminal and a second terminal, the first terminal of the third resistor being coupled to the second terminal of the second resistor and the second terminal of the third resistor being coupled to the second terminal of the capacitor and to the output terminal of the amplifier; a transistor having a first current terminal, a second current terminal and a control terminal, the first current terminal of the transistor being coupled to the first terminal of the first resistor, a first terminal of the capacitor and the input terminal of the amplifier, the second current terminal of the transistor being coupled to the second terminal of the third resistor, the second terminal of the capacitor and the output terminal of the amplifier, and the control terminal of the transistor being coupled to the second terminal of the first resistor and the first terminal of the second resistor; The circuit includes:

6. 6. The circuit of claim 5, the transistor is a first transistor, the diode circuit element further includes a second transistor having a first current terminal, a second current terminal, and a control terminal; a first current terminal of the second transistor coupled to the first terminal of the first resistor, the first current terminal of the first transistor, the first terminal of the capacitor, and the input terminal of the amplifier, a second current terminal of the second transistor coupled to the second terminal of the third resistor, the second current terminal of the first transistor, the second terminal of the capacitor, and the output terminal of the amplifier, and a control terminal of the second transistor coupled to the second terminal of the second resistor and the first terminal of the third resistor.

7. A bandpass filter, a lossless integrator having an input terminal and an output terminal; a lossy integrator having an input terminal and an output terminal; Including, The input terminal of the lossy integrator is coupled to the output terminal of the lossless integrator, and the output terminal of the lossy integrator is coupled to the input terminal of the lossless integrator, the lossy integrator being an amplifier having an input terminal and an output terminal; a diode circuit element coupled to the input terminal of the amplifier and to the output terminal of the amplifier; Including, Bandpass filter.

8. 8. A bandpass filter according to claim 7, the lossy integrator includes a capacitor having a first terminal and a second terminal; The diode circuit element is a resistor having a first terminal and a second terminal, the first terminal of the resistor being coupled to the input terminal of the amplifier and to the first terminal of the capacitor, and the second terminal of the resistor being coupled to the output terminal of the amplifier and to the second terminal of the capacitor; a first diode having an anode terminal and a cathode terminal, the anode terminal of the first diode being coupled to the first terminal of the resistor, the first terminal of the capacitor, and the input terminal of the amplifier, and the cathode terminal of the first diode being coupled to the second terminal of the resistor, the second terminal of the capacitor, and the output terminal of the amplifier; a second diode having an anode terminal and a cathode terminal, the cathode terminal of the second diode being coupled to the first terminal of the resistor, the first terminal of the capacitor, and the input terminal of the amplifier, and the anode terminal of the second diode being coupled to the second terminal of the resistor, the second terminal of the capacitor, and the output terminal of the amplifier; , a bandpass filter.

9. 8. A bandpass filter according to claim 7, the lossy integrator includes a capacitor having a first terminal and a second terminal; The diode circuit element is a first resistor having a first terminal and a second terminal, the first terminal of the first resistor being coupled to the first terminal of the capacitor and to the input terminal of the amplifier; a second resistor having a first terminal and a second terminal, the first terminal of the second resistor being coupled to the second terminal of the first resistor and the second terminal of the second resistor being coupled to the second terminal of the capacitor and to the output terminal of the amplifier; a transistor having a first current terminal, a second current terminal and a control terminal, the first current terminal of the transistor being coupled to the first terminal of the first resistor, the first terminal of the capacitor and the input terminal of the amplifier, the second current terminal of the transistor being coupled to the second terminal of the second resistor, the second terminal of the capacitor and the output terminal of the amplifier, and the control terminal of the transistor being coupled to the second terminal of the first resistor and the first terminal of the second resistor; , a bandpass filter.

10. 8. A bandpass filter according to claim 7, the lossy integrator includes a capacitor having a first terminal and a second terminal; The diode circuit element is a first resistor having a first terminal and a second terminal, the first terminal of the first resistor being coupled to the first terminal of the capacitor and to the input terminal of the amplifier; a second resistor having a first terminal and a second terminal, the first terminal of the second resistor being coupled to the second terminal of the first resistor; a third resistor having a first terminal and a second terminal, the first terminal of the third resistor being coupled to the second terminal of the second resistor and the second terminal of the third resistor being coupled to the second terminal of the capacitor and to the output terminal of the amplifier; a transistor having a first current terminal, a second current terminal and a control terminal, the first current terminal of the transistor being coupled to the first terminal of the first resistor, the first terminal of the capacitor and the input terminal of the amplifier, the second current terminal of the transistor being coupled to the second terminal of the third resistor, the second terminal of the capacitor and the output terminal of the amplifier, and the control terminal of the transistor being coupled to the second terminal of the first resistor and the first terminal of the second resistor; , a bandpass filter.

11. 1. A filter circuit, comprising: an amplifier configured to amplify an input voltage, the input voltage being amplified based on a feedback resistor between an input and an output of the amplifier; a diode circuit element coupled between the input and the output of the amplifier, the diode circuit element configured to reduce the feedback resistance when the input voltage exceeds a threshold; A filter circuit comprising:

12. 12. The filter circuit of claim 11, wherein the threshold is a first threshold, and the diode circuit element is configured to reduce the feedback resistance when the input voltage falls below a second threshold.

13. 12. The filter circuit of claim 11, wherein the diode circuit element is configured to reduce the feedback resistance in response to being turned on.

14. 12. The filter circuit of claim 11, wherein the diode circuit element is configured to increase the feedback resistance when the input voltage falls below the threshold.

15. 1. A circuit comprising: an amplifier having an inverting input terminal, a non-inverting input terminal, an inverting output terminal, and a non-inverting input terminal; a first capacitor having a first terminal and a second terminal, the first terminal of the first capacitor being coupled to the inverting input terminal of the amplifier and the second terminal of the first capacitor being coupled to the non-inverting output terminal of the amplifier; a first diode circuit element having a first terminal and a second terminal, the first terminal of the first diode circuit element being coupled to the first terminal of the first capacitor and to the inverting input terminal of the amplifier, and the second terminal of the first diode circuit element being coupled to the second terminal of the first capacitor and to the non-inverting output terminal of the amplifier; a second capacitor having a first terminal and a second terminal, the first terminal of the second capacitor being coupled to the non-inverting input terminal of the amplifier and the second terminal of the second capacitor being coupled to the inverting output terminal of the amplifier; a second diode circuit element having a first terminal and a second terminal, the first terminal of the second diode circuit element being coupled to the first terminal of the second capacitor and to the non-inverting input terminal of the amplifier, and the second terminal of the second diode circuit element being coupled to the second terminal of the second capacitor and to the inverting output terminal of the amplifier; The circuit includes:

16. 16. The circuit of claim 15, further comprising a lossless integrator having a first input terminal, a second input terminal, a first output terminal, and a second output terminal, wherein the first input terminal of the lossless integrator is coupled to the non-inverting output terminal of the amplifier, the second input terminal of the lossless integrator is coupled to the inverting output terminal of the amplifier, the first output terminal of the lossless integrator is coupled to the inverting input terminal of the amplifier through a first resistor, and the second output terminal of the lossless integrator is coupled to the non-inverting input terminal of the amplifier through a second resistor.

17. 16. The circuit of claim 15, wherein the first diode circuit element comprises: a resistor having a first terminal and a second terminal, the first terminal of the resistor being coupled to the inverting input terminal of the amplifier and to the first terminal of the first capacitor, and the second terminal of the resistor being coupled to the non-inverting output terminal of the amplifier and to the second terminal of the first capacitor; a first diode having an anode terminal and a cathode terminal, the anode terminal of the first diode being coupled to the first terminal of the resistor, the first terminal of the first capacitor, and the inverting input terminal of the amplifier, and the cathode terminal of the first diode being coupled to the second terminal of the resistor, the second terminal of the first capacitor, and the non-inverting output terminal of the amplifier; a second diode having an anode terminal and a cathode terminal, the cathode terminal of the second diode being coupled to the first terminal of the resistor, the first terminal of the first capacitor, and the inverting input terminal of the amplifier, and the anode terminal of the second diode being coupled to the second terminal of the resistor, the second terminal of the first capacitor, and the non-inverting output terminal of the amplifier; The circuit includes:

18. 16. The circuit of claim 15, wherein the first diode circuit element comprises: a first resistor having a first terminal and a second terminal, the first terminal of the first resistor being coupled to the first terminal of the first capacitor and to the inverting input terminal of the amplifier; a second resistor having a first terminal and a second terminal, the first terminal of the second resistor being coupled to the second terminal of the first resistor and the second terminal of the second resistor being coupled to the second terminal of the first capacitor and to the non-inverting output terminal of the amplifier; a transistor having a first current terminal, a second current terminal and a control terminal, the first current terminal of the transistor being coupled to the first terminal of the first resistor, the first terminal of the first capacitor and the inverting input terminal of the amplifier, the second current terminal of the transistor being coupled to the second terminal of the second resistor, the second terminal of the first capacitor and the non-inverting output terminal of the amplifier, and the control terminal of the transistor being coupled to the second terminal of the first resistor and the first terminal of the second resistor; The circuit includes:

19. 20. The circuit of claim 18, the transistor is a first transistor, the first diode circuit element comprising: a third resistor having a first terminal and a second terminal, the first terminal of the third resistor being coupled to the first terminal of the first capacitor, the inverting input terminal of the amplifier, the first terminal of the first resistor, and the first current terminal of the first transistor; a fourth resistor having a first terminal and a second terminal, the first terminal of the fourth resistor being coupled to the second terminal of the third resistor and the second terminal of the fourth resistor being coupled to the second terminal of the first capacitor, the non-inverting output terminal of the amplifier, the second terminal of the second resistor, and the second current terminal of the first transistor; a second transistor having a first current terminal, a second current terminal and a control terminal, the first current terminal of the second transistor being coupled to the first terminal of the first resistor, the first terminal of the third resistor, the first current terminal of the first transistor, the first terminal of the first capacitor, and the inverting input terminal of the amplifier, the second current terminal of the second transistor being coupled to the second terminal of the second resistor, the second terminal of the fourth resistor, the second current terminal of the first transistor, the second terminal of the first capacitor, and the non-inverting output terminal of the amplifier, and the control terminal of the second transistor being coupled to the second terminal of the third resistor and the first terminal of the fourth resistor; The circuit further comprises:

20. 16. The circuit of claim 15, wherein the first diode circuit element comprises: a first resistor having a first terminal and a second terminal, the first terminal of the first resistor being coupled to the first terminal of the first capacitor and to the inverting input terminal of the amplifier; a second resistor having a first terminal and a second terminal, the first terminal of the second resistor being coupled to the second terminal of the first resistor; a third resistor having a first terminal and a second terminal, the first terminal of the third resistor being coupled to the second terminal of the second resistor and the second terminal of the third resistor being coupled to the second terminal of the first capacitor and to the non-inverting output terminal of the amplifier; a transistor having a first current terminal, a second current terminal and a control terminal, the first current terminal of the transistor being coupled to the first terminal of the first resistor, the first terminal of the first capacitor and the inverting input terminal of the amplifier, the second current terminal of the transistor being coupled to the second terminal of the third resistor, the second terminal of the first capacitor and the non-inverting output terminal of the amplifier, and the control terminal of the transistor being coupled to the second terminal of the first resistor and the first terminal of the second resistor; The circuit includes:

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