Burst noise (pcn) reduction in audio drivers

Abstract

The embodiment of the invention relates to bursting noise PCN reduction in an audio driver. In some examples, a circuit (104) includes a first transistor (226) having a control terminal and first and second terminals. The circuit also includes a first capacitor (228) having a first terminal and a second terminal, the first terminal of the first capacitor coupled to the control terminal of the first transistor, and the second terminal of the first capacitor coupled to the second terminal of the first transistor. The circuit also includes a first switch (224) having a first terminal and a second terminal, the second terminal of the first switch coupled to the control terminal of the first transistor. The circuit also includes a second capacitor (222) having a first terminal and a second terminal, the first terminal of the second capacitor coupled to the first terminal of the first transistor, and the second terminal of the second capacitor coupled to the first terminal of the first switch.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Indian Provisional Patent Application No. 202341048864 filed on July 20, 2023, entitled “METHODS TO REDUCE POP-CLICK-NOISE (PCN) IN HIGH PERFORMANCE AUDIO DACS WITH UNIPOLAR HEADPHONE DRIVERS” and is hereby incorporated by reference in its entirety. Technical Field

[0003] Embodiments of the present application relate to pop-noise (PCN) reduction in audio drivers. Background Art

[0004] The audio output driver of the audio signal chain provides an analog signal to a device that can convert the analog signal into sound waves so that the user can hear the audio signal. Certain circuit conditions such as power on, power off, enabling the audio driver, or chopping in the audio signal chain can generate pop noise (PCN). Summary of the invention

[0005] In some examples, a circuit includes a first transistor having a control terminal and a first terminal and a second terminal. The circuit also includes a first capacitor having a first terminal and a second terminal, the first terminal of the first capacitor being coupled to the control terminal of the first transistor, and the second terminal of the first capacitor being coupled to the second terminal of the first transistor. The circuit also includes a first switch having a first terminal and a second terminal, the second terminal of the first switch being coupled to the control terminal of the first transistor. The circuit also includes a second capacitor having a first terminal and a second terminal, the first terminal of the second capacitor being coupled to the first terminal of the first transistor, and the second terminal of the second capacitor being coupled to the first terminal of the first switch.

[0006] In some examples, a circuit includes a first amplifier having an output terminal and first and second input terminals. The circuit also includes a first capacitor having a first terminal and a second terminal, the first terminal of the first capacitor being coupled to the second input terminal of the first amplifier. The circuit also includes a first switch having a first terminal and a second terminal, the first terminal of the first switch being coupled to the first terminal of the first capacitor. The circuit also includes a second capacitor having a first terminal and a second terminal, the first terminal of the second capacitor being coupled to the second terminal of the first switch.

[0007] In some examples, a system includes a first amplifier. The first amplifier has an output terminal and has a first input terminal and a second input terminal. The first amplifier includes a first transistor having a control terminal and a first terminal and a second terminal. The first amplifier also includes a first capacitor having a first terminal and a second terminal, the first terminal of the first capacitor being coupled to the control terminal of the first transistor, and the second terminal of the first capacitor being coupled to the second terminal of the first transistor. The first amplifier also includes a first switch having a first terminal and a second terminal, the second terminal of the first switch being coupled to the control terminal of the first transistor. The first amplifier also includes a second capacitor having a first terminal and a second terminal, the first terminal of the second capacitor being coupled to the first terminal of the first transistor, and the second terminal of the second capacitor being coupled to the first terminal of the first switch. The system also includes a second amplifier having an output terminal and a first input terminal and a second input terminal. The system also includes a third capacitor having a first terminal and a second terminal, the first terminal of the third capacitor being coupled to the second input terminal of the second amplifier. The system also includes a second switch having a first terminal and a second terminal, the first terminal of the second switch being coupled to the first terminal of the third capacitor. The system also includes a fourth capacitor having a first terminal and a second terminal, the first terminal of the fourth capacitor being coupled to the second terminal of the second switch. The system also includes a first resistor having a first terminal and a second terminal, the first terminal of the first resistor being coupled to the first input terminal of the second amplifier, and the second terminal of the first resistor being coupled to the first input terminal of the first amplifier. The system also includes a second resistor having a first terminal and a second terminal, the first terminal of the second resistor being coupled to the first input terminal of the second amplifier, and the second terminal of the second resistor being coupled to the second input terminal of the first amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a block diagram of an exemplary audio driver.

[0009] Figure 2 is a schematic diagram of an exemplary amplifier.

[0010] Figure 3A and 3B (which may collectively be referred to as FIG. 3 ) are diagrams of exemplary signal waveforms.

[0011] Figure 4 is a flow chart of an exemplary method.

[0012] Figure 5 is a schematic diagram of an exemplary audio driver.

[0013] Fig. 6A and 6B (which may collectively be referred to as FIG. 6 ) are diagrams of exemplary signal waveforms.

[0014] Figure 7 is a flow chart of an exemplary method. DETAILED DESCRIPTION

[0015] As described above, the audio driver provides an analog signal to a device capable of converting the analog signal into a sound wave so that the user can hear the audio signal. Certain circuit conditions in the audio driver can produce pop noise (PCN). For example, by rapidly changing the current flowing into the output or a capacitor in series decoupling the driver, PCN can be heard in the resulting sound wave. Similarly, enabling chopping can produce voltage ripple, which in turn can cause a step change in the output voltage of the audio driver, which can cause additional PCN. Such PCN can result in an undesirable or unpleasant user experience and may be unsuitable for audio drivers specified for high-performance application environments.

[0016] Examples of the present disclosure mitigate the occurrence of PCN in sound waves generated by the output signal of an audio driver. In a first example, a filter is coupled across the output transistor of the driver. In some examples, the filter is implemented as a capacitor coupled between the gate and drain of the transistor. In this way, the capacitor may be referred to as a Miller capacitor, so that the capacitor has a capacitance value that is subject to Miller multiplication (e.g., an increased capacitance value produced by Miller multiplication). This may enable the capacitor to have a smaller area while having a substantially equivalent effective capacitance compared to another capacitor (or filter) that is not coupled to the output transistor in a manner that is subject to Miller multiplication. In some examples, the capacitor is a switched capacitor, so that the filter is a switched Miller capacitor filter. In an example, the filter slows down or reduces the rate of change (e.g., slew rate) of the voltage provided at the control terminal or gate of the output transistor. The reduced slew rate of the voltage at the control terminal of the output transistor may correspond to a reduction in the slew rate of the current flowing through the output transistor. By reducing the slew rate of the current flowing through the output transistor, the rate at which the current flows into the output capacitor is slowed down, thereby alleviating the occurrence of PCN generated by the rapid change of the current in the output capacitor.

[0017] In a second example, the audio driver may implement chopping to increase the dynamic range and reduce total harmonic distortion plus noise, and thereby perform the performance of the audio driver. However, this chopping may produce increased voltage ripple, causing a step change in the voltage in the output signal of the audio driver. For example, chopping may produce voltage ripple based on the difference in value between the output common-mode voltage of the audio driver and the input common-mode voltage of the audio driver. In an example, chopping can be started without introducing voltage ripple by controlling the audio driver to prevent the start of chopping until the input common mode is approximately equal to the output common-mode voltage. The input common-mode voltage may then change logarithmically from the output common-mode voltage. In this way, the voltage ripple in the output voltage of the audio driver may also increase logarithmically or slowly and in a controlled manner. This slow increase in voltage ripple can reduce the voltage ripple that produces PCN in the output signal of the audio driver.

[0018] Figure 11 is a block diagram of an exemplary audio system 100. In some examples, the audio system 100 includes a digital-to-analog converter (DAC) 102, an audio driver 104, a resistor 106, a capacitor 108, and an audio device 110. In some examples, the audio driver 104 is a class AB driver, such as a class AB headphone driver. In some examples, the audio system 100 includes a slew limit circuit 112. In other examples, the audio system 100 includes a ripple limit circuit 114. In still other examples, the audio system 100 includes both the slew limit circuit 112 and the ripple limit circuit 114. In some examples, the audio driver 104 includes one or both of the slew limit circuit 112 and / or the ripple limit circuit 114. In an example, the DAC 102 is a delta-sigma DAC, while in other examples, the DAC 102 operates according to any suitable method and has any suitable architecture. In some examples, the audio device 110 is a headphone. In other examples, the audio device 110 is a speaker, a transducer, or any other device capable of converting an analog voltage into sound waves. In at least some examples, the audio device is a ground-centered audio device coupled to the audio system 100 through the capacitor 108. In some examples, the audio system 100 also includes a controller 116. In other examples, the controller 116 is implemented external to the audio system 100 and can be coupled to the audio system 100.

[0019] In an example, the DAC 102 has an output terminal and has an input terminal coupled to a digital data input terminal 115 of the audio system 100. The audio driver 104 has a first input terminal, a second input terminal, and an output terminal. The first input terminal may be a negative or inverting input terminal and the second input terminal may be a positive or non-inverting input terminal. The first input terminal of the audio driver 104 may be coupled to the first output terminal of the DAC 102, and the second input terminal of the audio driver 104 may be coupled to a common mode reference voltage terminal 117 (e.g., an output common mode voltage (Vocm) may be received there). The resistor 106 has a first terminal coupled to the output terminal of the audio driver 104 and a second terminal coupled to the first input terminal of the audio driver 104. The capacitor 108 has a first terminal and a second terminal, the first terminal of the capacitor 108 being coupled to the output terminal of the audio driver 104. The audio device 110 has a first terminal and a second terminal, the first terminal of the audio device 110 being coupled to the second terminal of the capacitor 108, and the second terminal of the audio device 110 being coupled to a ground terminal, at which a ground voltage potential is provided.

[0020] As described above, current flowing into or out of the capacitor 108 greater than a threshold amount may generate PCN. For example, during startup of the audio system 100, current may flow into the capacitor 108 to establish a common-mode operating voltage of the audio system 100. Similarly, during shutdown of the audio system 100, current may flow out of the capacitor 108. In order to reduce the occurrence of PCN, the slew limit circuit 112 limits the current flow rate (e.g., slew rate) of the capacitor 108. For example, the slew limit circuit 112 may control the audio driver 104 to create a slow turn-on effect for the audio driver 104, thereby limiting the rate at which the audio driver 104 provides current to the capacitor 108. In this way, the slew limit circuit 112 may reduce the occurrence of PCN in the audio system 100 caused by a sudden change in current flowing into or out of the capacitor 108. Similarly, the audio driver 104 may implement chopping so as to reduce low-frequency noise in the output signal of the audio driver 104. However, this chopping may introduce chopping artifacts into the output signal of the audio driver 104, such as voltage ripple. This voltage ripple may also generate PCN. In order to reduce this occurrence of PCN, the ripple limiting circuit 114 may provide a reference voltage that varies logarithmically. The reference voltage may be based on Vocm of the audio driver 104 at a first time and based on the input common mode voltage (Vicm) of the amplifier at a second time. For example, Vocm may be filtered to provide a reference voltage so that the value of the reference voltage increases approximately logarithmically. In response to Vocm being approximately equal to Vicm, the ripple limiting circuit 114 or the controller 116 may control the audio driver 104 to start chopping. Similarly, the ripple limiting circuit 114 may begin to base the reference voltage on Vicm, which may be less than Vocm, so that the reference voltage decreases approximately logarithmically to approximately equal Vicm. In this way, the growth of the ripple voltage may be controlled by the ripple limiting circuit 114 to grow approximately logarithmically in value, thereby preventing sudden or large changes that may generate PCN.

[0021] In an example, the controller 116 controls at least some operations or functions of the audio system 100. For example, the controller 116 determines and / or provides control signals to control various switches (not shown) of the audio system 100, provide one or more reference voltages to the audio system 100, and the like. In an example, the controller 116 controls switching of a switched capacitor (not shown) (e.g., a switched Miller capacitor filter) implemented as or in the slew limiting circuit 112. In another example, the controller 116 controls chopping performed by the audio system 100, controls switching of switches (not shown) of the ripple limiting circuit 114, controls determining and / or providing a reference voltage to the ripple limiting circuit 114, and the like. Although Figure 1100 , but in some examples, the controller 116 has an output terminal coupled to the digital data input terminal 115 so as to provide a digital data signal (e.g., a digital audio signal). Although shown as being external to the audio system 100 , in some examples, the controller 116 may be included in the audio system 100 .

[0022] Figure 2 is a schematic diagram of an exemplary audio driver 104 including a slew limit circuit 112. In some examples, the audio driver 104 includes a differential amplifier 202, a resistor 204, a transistor 206, a switch 208, a transistor 210, a switch 212, a resistor 214, a switch 216, a switch 217, and a switch 219. In some examples, the audio driver 104 also includes a resistor 218. In other examples, the audio driver 104 is coupled to the resistor 218 such that the resistor 218 is external to the audio driver 104. Similarly, in some examples, the audio driver 104 includes the resistor 106 and / or the capacitor 108. However, in other examples, the audio driver 104 may be coupled to the resistor 106 and / or the capacitor 108 such that the resistor 106 and / or the capacitor 108 are external to the audio driver 104. In an example, slew limit circuit 112 includes switch 220, capacitor 222, switch 224, transistor 226, and capacitor 228. In some examples, transistor 226 is a field effect transistor (FET), such as a p-channel FET.

[0023] In an example, the differential amplifier 202 has a first input terminal and a second input terminal, and has an output terminal. The first input terminal may be a negative or inverting input terminal, and the second input terminal may be a positive or non-inverting input terminal. The output terminal of the differential amplifier 202 is coupled to a first terminal of a switch 220, which also has a second terminal. The capacitor 222 has a first terminal coupled to a supply voltage terminal 230, at which a voltage source (Vdd) is provided; and has a second terminal coupled to a second terminal of the switch 220. The switch 224 has a first terminal coupled to the second terminal of the switch 220, and has a second terminal. The transistor 226 has a control terminal coupled to the second terminal of the switch 224, a first terminal coupled to the supply voltage terminal 230, and has a second terminal. The capacitor 228 has a first terminal coupled to the control terminal of the transistor 226, and has a second terminal coupled to the second terminal of the transistor 226. The resistor 204 has a first terminal coupled to the second terminal of the transistor 226, and has a second terminal coupled to a ground terminal 231, at which a ground voltage potential is provided. As Figure 2, capacitor 228 may be referred to as a Miller capacitor having a capacitance value that is subject to Miller multiplication resulting from the topology of slew limit circuit 112. In an example, transistor 226 is a metal oxide semiconductor field effect transistor (MOSFET) such that its control terminal is a gate terminal and its second terminal is a drain terminal. When coupled across the gate and drain terminals of a MOSFET transistor (e.g., transistor 226), capacitor 228 appears larger from an electrical standpoint for small signals because its actual capacitance is multiplied by the transconductance of the MOSFET and the impedance at the drain terminal of the MOSFET, thereby resulting in a larger electrical or effective capacitance. This multiplication is referred to as Miller multiplication, and enables a capacitor having a first value of physical capacitance and consuming a first silicon area to have a second value of effective or electrical capacitance that is larger than the first value without increasing the physical size of the capacitor to be larger than the first silicon area.

[0024] Transistor 206 has a control terminal and a first terminal and a second terminal. The first terminal of transistor 206 is coupled to a supply voltage terminal 230. Switch 208 has a first terminal coupled to terminal 232 and has a second terminal coupled to the control terminal of transistor 206. In some examples, terminal 232 and terminal 234 are each coupled to an output terminal of amplifier 202 so that transistors 206, 210 can receive LOOP_CTRL as a gate control signal. In other examples, the gate control signal is received at terminals 232 and 234 (e.g., from controller 116 or from any other suitable source). For example, in some implementations, the audio driver 104 may include a second amplifier (not shown) having an input terminal coupled in parallel with the input terminal of amplifier 202 and having an output terminal that provides LOOP_CTRL. Although not shown in Figure 2 206, but in some examples, a voltage offset is applied to LOOP_CTRL by a voltage source (not shown) coupled between the output terminal of amplifier 202 and terminal 234 so as to bias LOOP_CTRL for operation with transistor 210. Transistor 210 has a control terminal and a first terminal and a second terminal. The first terminal of transistor 210 is coupled to the second terminal of transistor 206, and the second terminal of transistor 210 is coupled to ground terminal 231. Switch 212 has a first terminal coupled to terminal 234, and has a second terminal coupled to the control terminal of transistor 210.

[0025] Resistor 214 has a first terminal coupled to the second terminal of transistor 226, and has a second terminal. Switch 216 has a first terminal coupled to the second input terminal of differential amplifier 202, and has a second terminal coupled to the second terminal of resistor 214. Switch 217 has a first terminal and a second terminal, the first terminal coupled to the second terminal of transistor 206. In an example, resistor 218 has a first terminal coupled to the second terminal of transistor 226 and a second terminal coupled to the second terminal of switch 217. In other examples, resistor 218 may be coupled between the second terminal of transistor 226 and the second terminal of switch 217, but external to audio driver 104. Similarly, in an example, capacitor 108 may have a first terminal coupled to the first terminal of switch 217 and a second terminal coupled to or coupleable to audio device 110. In another example, the first terminal of capacitor 108 may be coupled to the first terminal of switch 217, but external to audio driver 104. Resistor 106 has a first terminal coupled to a first terminal of switch 217 and has a second terminal and, in at least some instances, is external to audio driver 104. Switch 219 has a first terminal coupled to a second terminal of resistor 106 and has a second terminal coupled to a second input terminal of differential amplifier 202.

[0026] In an example of operation of the audio driver 104, the differential amplifier 202 receives a differential input signal. For example, the differential amplifier 202 receives a positive component (INP) of the differential input signal at a first input terminal of the differential amplifier 202 and receives a negative component (INM) of the differential input signal at a second input terminal of the differential amplifier 202. The differential input signal may be received from any suitable source (e.g., Figure 1 DAC 102 shown in FIG. 1 receives a differential input signal. Differential amplifier 202 determines and provides a signal (LOOP_CTRL) representing the difference between INM and INP. In an example, slew limit circuit 112 determines or controls the slew rate of the voltage across resistor 218. For example, LOOP_CTRL may be a gate control signal for controlling transistor 226 and may be filtered by components of slew limit circuit 112. By filtering LOOP_CTRL switched by switches 220, 224 and capacitor 228, for example, by a filter formed by capacitor 222, the rate of change of charge at the control terminal of transistor 226 (e.g., the slew rate of the signal at the control terminal of transistor 226) is slowed down. By slowing the rate of change of charge at the control terminal of transistor 226, the rate of change of the current flowing through transistor 226 is also changed accordingly. For example, the rate of change or slew rate of charge at the control terminal of transistor 226 and flowing through transistor 226 may exhibit an approximately logarithmic response behavior over time.

[0027] In an example, switches 220, 224 receive CLK and CLKZ control signals, respectively. CLK and CLKZ are non-overlapping, anti-phase control signals so that at a given time, only one of switches 220, 224 is on. By switching switches 220, 224 to on and off states in a repetitive manner, capacitor 222 electrically acts as a resistor having a resistance of approximately 1 / Cf, where C is the capacitance of capacitor 222, and f is the frequency of CLK (or CLKZ). In this way, a resistor-capacitor (RC) filter is formed by capacitor 222 and capacitor 228. This RC filter causes the voltage provided at the control terminal of transistor 226 based on LOOP_CTRL to slowly decrease according to the time constant of the RC filter, thereby approximating a logarithmic response. The slow reduction of the voltage provided at the control terminal of transistor 226 correspondingly causes the voltage provided at the second terminal of transistor 226 to slowly increase in value, thereby also approximating a logarithmic response. This slow increase limits the rate at which current flows through transistor 226, through resistor 218, and into capacitor 108 to charge capacitor 108 to Vocm (e.g., the slew rate of capacitor 108). By limiting the slew rate of capacitor 108, voltage transients that may occur at audio device 110 may be limited. In at least some instances, voltage transients are limited to a magnitude of no greater than 500 microvolts (μV). By limiting voltage transients in this manner, audio PCN provided by audio device 110 resulting from the charging (or discharging) of capacitor 108 may be mitigated, thereby reducing or eliminating PCN. Additionally, by limiting the current through resistor 218, the resistance of resistor 218 may be reduced compared to an example of audio driver 104 in which slew limit circuit 112 is omitted. This reduction in the resistance of resistor 218 may correspondingly achieve a reduction in the physical area consumed by resistor 218, as well as a reduction in the amount of time for capacitor 108 to charge to Vocm.

[0028] In an example, switches 208, 212, 216, 217, 219 provide startup sequencing to the audio driver 104. For example, in response to detecting (e.g., by the controller 116 or any other suitable component) that the audio device 110 has been coupled to the capacitor 108, switches 208, 212, 216, and 219 are controlled to be non-conductive, and switches 216 and 217 are controlled to be conductive. Each of the switches 208, 212, 216, 217, 219 can be implemented in any suitable manner, the scope of which is not limited herein. In some examples, the switches 208, 212, 216, 217, 219 are implemented as transistors. Thus, switches 208, 212, 216, 217, 219 may each have a respective control terminal at which a signal is received whose value is related to the value of the signal at the other terminal of the switch and determines whether the switch is conductive (e.g., substantially closed or connected) or non-conductive (e.g., substantially open or disconnected). In some examples, at least some of switches 208, 212, 216, 217, 219 receive control signals from controller 116. In other examples, at least some of switches 208, 212, 216, 217, 219 receive control signals from any other suitable source, the scope of which is not limited herein. In response to the voltage of capacitor 108 increasing to be substantially equal to Vocm, switches 208, 212, and 219 are controlled to be conductive, and switches 216 and 217 are controlled to be non-conductive. In some examples, the determination of the voltage of capacitor 108 may be made at least in part by controller 116. In this manner, during the startup phase of operation of the driver 104, the slew limit circuit 112 can control the charging of the capacitor 108 to Vocm while preventing such charging from affecting the operation of the amplifier 202, the transistor 206, or the transistor 210. Similarly, after the startup phase of operation is complete, the slew limit circuit 112 can be electrically decoupled from the capacitor 108, thereby preventing the slew limit circuit 112 from affecting the quality of the audio output provided by the audio driver 104.

[0029] In an example, LOOP_CTRL is provided at terminal 232, and in some examples at terminal 234, while in other examples, a horizontally shifted version of LOOP_CTRL is provided at terminal 234. Based on control according to the value of LOOP_CTRL, transistors 206, 210 are either conductive or non-conductive to provide an output signal (Vout) of the audio driver 104 at the first terminal of the capacitor 108. In this way, transistors 206, 210 together provide an analog signal at the first terminal of the capacitor 108 that represents the differential input signal received by the amplifier 202, thereby generating an audio output signal of the audio driver 104.

[0030] FIG3 is a diagram 300 of an exemplary signal waveform. In an example, the diagram 300 represents at least some of the signals that may be present in the audio system 100 (eg, in or provided by the audio driver 104), as described above with respect to FIG. Figure 2 Described. In the example, the diagram 300 includes signals 301, 302, 303, 304, 305, and 306. Signal 301 represents the voltage provided at the control terminal of transistor 226 in the absence of the slew limit circuit 112, and is shown with a vertical axis representing the voltage in volts (V) and a horizontal axis representing the time in milliseconds (ms). Signal 302 represents the current flowing through transistor 226 in the absence of the slew limit circuit 112, and is shown with a vertical axis representing the current in milliamperes (mA) and a horizontal axis representing the time in ms. Signal 303 represents the voltage provided at the second terminal of transistor 226 in the absence of the slew limit circuit 112, and is shown with a vertical axis representing the voltage in V and a horizontal axis representing the time in ms. Signal 304 represents the voltage provided at the second terminal of transistor 206 in the absence of slew limit circuit 112 (e.g., where resistor 218 may have a greater resistance value and correspondingly greater physical size than an example including slew limit circuit 112), and is shown with a vertical axis representing voltage in V and a horizontal axis representing time in ms. Signal 305 is an amplified version of signal 304 representing the voltage provided at the second terminal of transistor 206 at the time when audio driver 104 is enabled in the absence of slew limit circuit 112, and is shown with a vertical axis representing voltage in millivolts (mV) and a horizontal axis representing time in ms. Signal 306 represents the voltage that may be generated attributable to a PCN in audio device 110 in the absence of slew limit circuit 112, and is shown with a vertical axis representing voltage in microvolts (μV) and a horizontal axis representing time in ms.

[0031] Similarly, diagram 300 also includes signals 311, 312, 313, 314, 315, and 316. Signal 311 represents the voltage provided at the control terminal of transistor 226 in the presence of slew limit circuit 112, and is shown with a vertical axis representing voltage in V and a horizontal axis representing time in ms. Signal 312 represents the current flowing through transistor 226 in the presence of slew limit circuit 112, and is shown with a vertical axis representing current in mA and a horizontal axis representing time in ms. Signal 313 represents the voltage provided at the second terminal of transistor 226 in the presence of slew limit circuit 112 (e.g., where resistor 218 may have a smaller value and correspondingly smaller physical size than in the absence of slew limit circuit 112), and is shown with a vertical axis representing voltage in V and a horizontal axis representing time in ms. Signal 314 represents the voltage provided at the second terminal of transistor 206 in the presence of slew limit circuit 112, and is shown with a vertical axis representing voltage in V and a horizontal axis representing time in ms. Signal 315 is an amplified version of signal 314 representing the voltage provided at the second terminal of transistor 206 in the presence of slew limit circuit 112, and is shown with a vertical axis representing voltage in mV and a horizontal axis representing time in ms. Signal 316 represents the voltage attributable to a PCN in audio device 110 in the presence of slew limit circuit 112, and is shown with a vertical axis representing voltage in μV and a horizontal axis representing time in ms.

[0032] As shown by comparison signals 301, 311, the slew limit circuit 112 filters the voltage provided at the control terminal of transistor 226, thereby reducing the rate of change of the voltage. Correspondingly, as shown by comparison signals 302, 312 with signals 303, 313, the rate of increase of the current flowing through transistor 226 and therefore the voltage provided at the second terminal of transistor 226 is also reduced. As shown by comparison signals 305, 316, signal 305 includes a fast initial jump in value, followed by a substantially linear response. The fast initial jump in value can produce PCN, as described above. Through the implementation of the slew limit circuit 112, the value of signal 315 increases more slowly in a substantially logarithmic manner. This can achieve a reduction in the resistance and size of resistor 218, as described above, and a corresponding reduction in the startup time of the audio driver 104. Similarly, as shown by comparing signals 306, 316, the slew rate of the signals 311 and, correspondingly, 312, 313, 314, and 315 is limited by the slew rate of the slew limit circuit 112, and the magnitude of the PCN in the audio device 110 is reduced. Therefore, the presence of the slew limit circuit 112 in the audio driver 104 limits the occurrence of PCN in the audio device 110, thereby improving the user experience of the user driving the audio device 110 via the audio system 100, while also facilitating a reduction in the startup time of the audio driver 104.

[0033] Figure 4 4 is a flow chart of an exemplary method 400. In an example, the method 400 is implemented by the audio system 100, such as at least partially by the audio driver 104 and / or the controller 116. In an example, the method 400 is implemented to limit the slew rate of an output capacitor (e.g., capacitor 108) of the audio system 100. The method 400 may be implemented to limit the slew rate of the output capacitor to reduce the occurrence of PCN in an audio device, such as the audio device 110, which is coupled to the output capacitor and receives a signal for conversion from an analog voltage to an audible sound wave via the output capacitor.

[0034] At operation 402, an input signal is received. The input signal may be received, for example, from a DAC. In an example, the input signal is a differential signal representing an audio frequency for output as an audio signal by the audio driver 104.

[0035] At operation 404, a gate control signal is determined based on a difference between the input signal and the feedback signal. In some examples, the feedback signal forms a second component of the differential signal, such as a negative component. In some examples, the difference may be determined by a differential amplifier.

[0036] At operation 406, Vocm is provided based on the gate control signal. For example, the gate control signal is filtered and provided to the control terminal of the transistor. In some examples, the filtering is performed at least in part by a capacitor coupled in a Miller arrangement. In an example, the capacitor is capacitor 228, as described above, and forms an RC filter with a switched capacitor (e.g., capacitor 222), which electrically approximates a resistor. By filtering the gate control signal, the rate of change of the charge at the control terminal of the control transistor is increased in a roughly logarithmic manner. Accordingly, the change in the current flowing through the transistor also occurs roughly logarithmically. Therefore, Vocm increases logarithmically, rather than increasing in a sudden or stepwise manner. By limiting the rate of change or slew rate of Vocm, the current flowing into the output capacitor is reduced, and thus the voltage transients occurring in the audio device coupled to the output capacitor are reduced. Therefore, the PCN occurring in the audio device is reduced due to the use of a capacitor to filter the gate control signal of the transistor, which generates current to provide Vocm.

[0037] At operation 408, an analog signal representing the input signal is provided at the output capacitor. In some examples, the analog signal is formed based on control of the differential output stage according to the gate control signal. In an example, the analog signal can be converted by the audio device into a sound wave representing the input signal.

[0038] Figure 5 is a schematic diagram of an exemplary audio driver 500. In some examples, the audio driver 500 is suitable for implementation as Figure 1 In some examples, the audio driver 500 includes an audio driver 104, a resistor 106, a chopper circuit 506, a resistor 508, a resistor 510, an amplifier 512, a resistor 514, a resistor 516, an amplifier 518, a resistor 520, and a ripple limiting circuit 114. Figure 5 104, but in various examples, at least some of the components or circuits shown external to the audio driver 104 may instead be implemented within the audio driver 104, or as part of the audio driver, on the same substrate or semiconductor die as the audio driver 104, etc. In some examples, the audio driver 104 may have the components described above with respect to Figure 2 For example, Figure 5 The audio driver 104 shown in FIG. 1 may include a slew limit circuit 112, as described above, and with respect to FIG. Figure 5The description thereof is not included again. In other examples, the audio driver 104 may have any other suitable architecture and feature set, such as omitting the slew limiter circuit 112, the scope of which is not limited herein. In some examples, the ripple limiter circuit 114 includes a switch 522, a capacitor 524, a switch 526, and a capacitor 528.

[0039] In an example, the audio driver 104 has a first input terminal and a second input terminal and an output terminal, as described above. The resistor 106 has a first terminal coupled to the output terminal of the audio driver 104, and has a second terminal coupled to the first input terminal of the audio driver 104. The chopping circuit 506, which may have any suitable architecture for performing signal chopping, for example, via two or more switches (not shown), has a first input terminal and a second input terminal, and a first output terminal and a second output terminal. In some examples, the chopping circuit 506 has one or more control terminals (not shown) coupled to the controller 116 to receive a control signal from the controller 116. The first output terminal of the chopping circuit 506 is coupled to the first input terminal of the audio driver 104, and the second output terminal of the chopping circuit 506 is coupled to the second input terminal of the audio driver 104. The resistor 508 has a first terminal and a second terminal, and the second terminal of the resistor 508 is coupled to the first input terminal of the chopping circuit 506. The resistor 510 has a first terminal and a second terminal, and the second terminal of the resistor 510 is coupled to the second input terminal of the chopping circuit 506. Amplifier 512 has a first input terminal and a second input terminal, and has an output terminal. The output terminal of amplifier 512 is coupled to a first terminal of resistor 508 and to a first terminal of resistor 510. Resistor 514 has a first terminal and a second terminal, the first terminal is coupled to the first input terminal of amplifier 512, and the second terminal is coupled to the first input terminal of audio driver 104. Resistor 516 has a first terminal and a second terminal, the first terminal is coupled to the first input terminal of amplifier 512, and the second terminal is coupled to the second input terminal of audio driver 104. Amplifier 518 has a first input terminal and a second input terminal, and has an output terminal. The first input terminal of amplifier 518 is coupled to the output terminal of audio driver 104, and the second input terminal of amplifier 518 is coupled to the output terminal of amplifier 518. Resistor 520 has a first terminal and a second terminal, the first terminal of resistor 520 is coupled to the second input terminal of audio driver 104, and the second terminal of resistor 520 is coupled to the output terminal of amplifier 518. In an example, the DAC 102 is a differential DAC such that a first differential output terminal of the DAC 102 is coupled to a first input terminal of the audio driver 104 , and a second differential output terminal of the DAC 102 is coupled to a second input terminal of the audio driver 104 .

[0040] The switch 522 has a first terminal and a second terminal, the first terminal of the switch 522 being coupled to the reference signal terminal 530. The capacitor 524 has a first terminal and a second terminal, the first terminal of the capacitor 524 being coupled to the second terminal of the switch 522, and the second terminal of the capacitor 524 being coupled to the ground terminal 532. The switch 526 has a first terminal and a second terminal, the first terminal of the switch 526 being coupled to the second input terminal of the amplifier 512, and the second terminal of the switch 526 being coupled to the first terminal of the capacitor 524. The capacitor 528 has a first terminal and a second terminal, the first terminal of the capacitor 528 being coupled to the second input terminal of the amplifier 512, and the second terminal of the capacitor 528 being coupled to the ground terminal 532.

[0041] In an example of operation of the audio driver 500, in response to detecting (e.g., by the controller 116 or any other suitable component) that the audio device 110 has been coupled to the capacitor 108, a reference signal having a first value is provided at a first input terminal of the amplifier 518 and at a first time at the terminal 530. In some examples, the reference signal is provided by the controller 116. In other examples, the reference signal is provided by any suitable voltage or signal source (not shown), the scope of which is not limited herein. In some examples, also in response to detecting that the audio device 110 has been coupled to the capacitor 108, the capacitor 108 is charged to the value of the reference signal. The capacitor 108 can be charged to Vocm in any suitable manner, including at least via the implementation of the slew limit circuit 112, as described above.

[0042] At a second time that occurs subsequently, a reference signal having a second value is provided at the reference signal terminal 530. The reference signal may again be provided by the controller 116 or by any other suitable voltage or signal source, the scope of which is not limited herein. In some instances, the first value is approximately equal to Vocm. In some instances, the second value is approximately equal to Vicm, which may be a common-mode voltage between the first input terminal and the second input terminal of the audio driver 104. In at least some instances, Vicm is less than Vocm. The reference signal may be filtered by the ripple limiting circuit 114, for example, via a switched capacitor RC filter formed by capacitors 524, 528 and switches 522, 526, to form a filtered reference signal provided at the second input terminal of the amplifier 512. The switched capacitor RC filter may operate in a manner substantially similar to the RC filter formed by capacitors 222, 228 and switches 220, 224 of the slew limiting circuit 112, as described above, but without the Miller multiplication effect of capacitor 228. Thus, with respect to Figure 5The description of the filtering action of the switched capacitor RC filter is not repeated. In an example, switches 522, 526 may be implemented in any suitable manner, the scope of which is not limited herein. In some examples, switches 522, 526 are implemented as transistors. Thus, switches 522, 526 may each have a corresponding control terminal, at which a signal is received, the value of which is related to the value of the signal at the other terminal of the switch and determines whether the switch is conductive (e.g., substantially closed or connected) or non-conductive (e.g., substantially open or disconnected). In some examples, at least some of switches 522, 526 receive control signals from controller 116. In other examples, at least some of switches 522, 526 receive control signals from any other suitable source, the scope of which is not limited herein.

[0043] In response to the value of the filtered reference signal increasing to be approximately equal to Vocm, there is almost no voltage difference across the resistors 508, 510, and thus almost no current flows through the resistors 508, 510. Therefore, in response to the value of the filtered reference signal increasing to be approximately equal to Vocm, the controller 116 or another suitable control device can control the chopping circuit 506 to start chopping. Also in response to the value of the filtered reference signal increasing to be approximately equal to Vocm, the value of the reference signal provided at the reference signal terminal 530 can transition from a first value to a second value. Therefore, the value of the filtered reference signal can decrease approximately logarithmically from about Vocm to about Vicm.

[0044] Because the value of the filtered reference signal decreases at a rate that approximates a logarithmic response, the difference between Vocm and Vicm increases at a corresponding approximate logarithmic rate. Therefore, the voltage across the resistors 508, 510 and therefore the amount of current flowing through the resistors 508, 510 also increases at a corresponding approximate logarithmic rate. The chopping circuit 506 that chops the signal received from the resistors 508, 510 may produce a chopping artifact (e.g., a voltage ripple generated by a mismatch between the two resistors 508, 510 or any other element being chopped) reflected in the output signal of the amplifier 104, which has a magnitude that is approximately proportional to the current flowing through the resistors 508, 510. Therefore, the voltage difference between Vocm and Vicm is controlled to occur in an approximately logarithmic manner by the ripple limiting circuit 114, and the voltage ripple in Vout is correspondingly controlled to increase in an approximately logarithmic manner. By limiting the rate of increase of the voltage ripple in Vout, the magnitude of PCN in the audio device 110 is reduced. Therefore, the ripple limiting circuit 114 of the audio driver 500 limits the occurrence of PCN in the audio device 110 , thereby improving the user experience of the user driving the audio device 110 via the audio driver 500 .

[0045] In an example, the amplifier 512 receives a filtered reference signal and a signal representing an average value of the signal provided at the first input terminal and the second input terminal of the audio driver 104. The amplifier 512 provides an output signal representing the difference between the filtered reference signal and the average value of the signal provided at the first input terminal and the second input terminal of the audio driver 104. The output signal is provided to resistors 508, 510, which provide the output signal to the chopping circuit 506. The chopping circuit 506 performs signal chopping according to any suitable process, the scope of which is not limited herein, to provide a signal at the first input terminal and the second input terminal of the audio driver 104 so as to cause the audio driver 104 to provide an output signal having a value of approximately Vocm for charging the capacitor 108, as described herein. Subsequently, a differential input signal (e.g., formed by INM and INP) may be received, for example, from the DAC 102 for driving the audio device 110 coupled to the capacitor 108 so that the audio device 110 generates a sound wave based on the differential input signal.

[0046] FIG6 is a diagram 600 of an exemplary signal waveform. In an example, diagram 600 represents at least some of the signals that may be present in audio system 100, as described above with respect to FIG. Figure 5 Described. In the example, the diagram 600 includes signals 601, 602, 603, 605, 608, and 610. Signal 601 represents the reference signal after filtering in the presence of the ripple limiting circuit 114, and is shown with a vertical axis representing the voltage in V and a horizontal axis representing the time in ms. Signal 602 represents the voltage drop across resistors 508, 510 in the presence of the ripple limiting circuit 114, and is shown with a vertical axis representing the voltage in mV and a horizontal axis representing the time in ms. Signal 603 represents the signal provided at the second terminal of the capacitor 108 in the presence of the ripple limiting circuit 114, and is shown with a vertical axis representing the voltage in V and a horizontal axis representing the time in ms. Signal 605 represents the voltage of PCN in the signal 603 in the presence of the ripple limiting circuit 114, and is shown with a vertical axis representing the voltage in μV and a horizontal axis representing the time in ms. Signal 608 represents signal 602 with a vertical axis representing voltage in mV and a horizontal axis representing time in microseconds (μs). Signal 610 represents signal 603 shown with a vertical axis representing voltage in mV and a horizontal axis representing time in μs.

[0047] Similarly, the diagram 600 also includes signals 621, 622, 623, 624, 626, 627, and 629. Signal 621 represents the filtered reference signal (e.g., a substantially constant value substantially equal to Vicm) in the absence of the ripple limiting circuit 114, and is shown with a vertical axis representing voltage in V and a horizontal axis representing time in ms. Signal 622 represents the voltage drop across resistors 508, 510 in the absence of the ripple limiting circuit 114, and is shown with a vertical axis representing voltage in mV and a horizontal axis representing time in ms. Signal 623 represents the signal provided at the second terminal of the capacitor 108 in the absence of the ripple limiting circuit 114, and is shown with a vertical axis representing voltage in V and a horizontal axis representing time in ms. Signal 624 represents the voltage of PCN in signal 623 in the absence of ripple limiting circuit 114, and is shown with a vertical axis representing voltage in μV and a horizontal axis representing time in ms. Signal 626 represents a chopping enable signal that controls the operation of chopping circuit 506 in the absence of ripple limiting circuit 114, and is shown with a vertical axis representing voltage in V and a horizontal axis representing time in μs. Signal 627 represents signal 622 with a vertical axis representing voltage in mV and a horizontal axis representing time in μs. Signal 629 represents signal 623 shown with a vertical axis representing voltage in mV and a horizontal axis representing time in μs.

[0048] As shown by comparison signals 601, 621, the ripple limiting circuit 114 causes the value of the filtered reference signal to slowly decrease approximately logarithmically to approach Vicm (e.g., from Vocm), rather than maintaining an approximately constant value. This slow decrease in the value of the filtered reference signal causes the value of the voltage drop across resistors 508, 510 to slowly, again approximately logarithmically, increase from about 0, rather than maintaining an approximately constant value, as shown by signals 602, 622 and 627, 608. As shown by comparison signals 603, 623, this slow increase in the voltage drop across resistors 508, 510 causes an approximately logarithmic increase in the value of the output signal of the audio system 100, as described elsewhere herein. An amplified version of signals 603, 623 showing the onset of ripple growth is shown by signals 608, 610. This logarithmic increase in the value of the output signal of the audio system 100 produces a reduced PCN, such as described above with respect to Figure 5 Described and shown by signals 624 , 605 .

[0049] Figure 7is a flow chart of an exemplary method 700. In an example, the method 700 is implemented at least in part by the audio driver 500 and / or the controller 116. In an example, the method 700 is implemented to limit the slew rate of the voltage ripple in Vout provided by the audio driver 500. The method 700 may be implemented to limit the slew rate of the voltage ripple to reduce the occurrence of PCN in an audio device, such as the audio device 110, which is coupled to the output capacitor and receives a signal for conversion from an analog voltage to an audible sound wave via the output capacitor.

[0050] At operation 702, a reference signal having a first value is received. The reference signal may be received, for example, in response to an audio device being coupled to an audio driver or an audio system. The reference signal may be received from any suitable source, the scope of which is not limited herein.

[0051] At operation 704, Vout is provided based on the reference signal, Vout including a common mode component Vocm. In some examples, Vout is provided by an audio driver such as audio driver 104, as described above with respect to Figure 2 described, or provided by any other suitable analog amplifier or driver.

[0052] At operation 706, a filtered reference signal is provided based on the reference signal. In some examples, the first value is substantially equal to Vocm. Thus, the filtered reference signal may have a substantially logarithmically increasing value starting at substantially zero volts and increasing to substantially equal to Vocm.

[0053] At operation 708, in response to the value of the filtered reference signal increasing to be approximately equal to Vocm, a chopping circuit is enabled. In some examples, the chopping circuit chops a signal representing the difference between the filtered reference signal and the average value of the signal provided at the first input terminal and the second input terminal of the audio driver 104. For example, the chopping circuit may be a chopping circuit 506, which may chop the output signal of the amplifier 502. The chopping circuit may be controlled to start chopping in any suitable manner based on the architecture of the chopping circuit and by any suitable device such as the controller 116. In an example, at the time when the chopping circuit is enabled, since the filtered reference signal is approximately equal to Vocm, almost no current can flow through the resistors 106, 508, 510, or 520. Therefore, the output signal of the amplifier 512 will have a value approximately equal to Vocm.

[0054] At operation 710, a filtered reference signal is provided based on a reference signal having a second value, also in response to the value of the filtered reference signal increasing to be approximately equal to Vocm. In some instances, the second value is approximately equal to Vicm. In this way, the reference signal can be considered a variable value reference signal, having a first value at a first time and a second value at a second time. Therefore, the filtered reference signal can have a value that starts at approximately Vocm and decreases to a value that is approximately logarithmically reduced to be approximately equal to Vicm. In this way, the voltage drop across the resistors 106, 508, 510, 520 and therefore the current flowing through the resistors 106, 508, 510, 520 can be controlled to increase in an approximately logarithmic manner. This approximately logarithmic increase can cause the voltage ripple that occurs in Vout due to chopping to increase in a logarithmic manner from a magnitude of approximately zero volts, thereby limiting the occurrence of PCN generated by the voltage ripple. In at least some instances, the voltage ripple is limited to a peak-to-peak amplitude of approximately 100 μV.

[0055] In this specification, the term "coupled" may encompass connections, communications, or signal paths that enable a functional relationship consistent with this specification. For example, if device A generates a signal to control device B to perform an action, then: (a) in a first instance, device A is coupled to device B through a direct connection; or (b) in a second instance, device A is coupled to device B through an intermediate component C, provided that the intermediate component C does not change the functional relationship between device A and device B so that device B is controlled by device A via the control signal generated by device A.

[0056] A device "configured to" perform a task or function may be configured (e.g., programmed and / or hardwired) to perform the function when manufactured by a manufacturer, and / or may be configured (or reconfigurable) by a user after manufacture to perform the function and / or other additional or alternative functions. The configuration may be through firmware and / or software programming of the device, through the construction and / or layout of the device's hardware components and interconnections, or a combination thereof.

[0057] Circuits or devices described herein as including certain components may alternatively be coupled to those components to form the described circuit systems or devices. For example, a structure described as including one or more semiconductor elements (e.g., transistors), one or more passive elements (e.g., resistors, capacitors, and / or inductors), and / or one or more sources (e.g., voltage sources and / or current sources) may alternatively include only semiconductor elements within a single physical device (e.g., a semiconductor die and / or an integrated circuit (IC) package), and may be coupled to at least some of the passive elements and / or sources to form the described structure at the time of manufacture or after manufacture, for example, by an end user and / or a third party.

[0058] Although some components may be described herein as belonging to a specific process technology, these components may be exchanged with components of other process technologies. The circuit described herein may be reconfigured to include a replaced component to provide functionality at least partially similar to the functionality available before the component replacement. Unless otherwise specified, a component shown as a resistor generally represents any one or more elements coupled in series and / or in parallel to provide the impedance amount represented by the displayed resistor. For example, a resistor or capacitor shown and described as a single component herein may alternatively be a plurality of resistors or capacitors coupled in parallel between the same nodes. For example, a resistor or capacitor shown and described as a single component herein may alternatively be a plurality of resistors or capacitors coupled in series between two nodes identical to a single resistor or capacitor. Various switches are shown and described herein. The switch may be implemented as an electromechanical device based on the application environment of the switch, or as a solid-state device. Although not necessarily explicitly shown or described herein, the switch may include a control terminal, at which a control signal is received to control the state of the switch, such as opening or closing, non-conducting or conducting, disconnecting or connecting, etc.

[0059] The use of the phrase "ground voltage potential" in the foregoing description includes chassis ground, ground wire ground, floating ground, virtual ground, digital ground, universal ground, and / or any other form of ground connection that is applicable or suitable for the teachings of this specification. In this specification, unless otherwise stated, "about", "approximately" or "substantially" preceding a parameter means within + / -10% of the parameter. Modifications are possible in the described examples, and other examples are possible within the scope of the claims.

[0060] As used herein, the terms "terminal", "node", "interconnect", "pin", and "lead" may be used interchangeably. Unless specifically stated to the contrary, these terms are generally used to mean an interconnect between device elements, circuit elements, integrated circuits, devices, or semiconductor components, or their terminations. In addition, a voltage rail or more simply a "rail" may also be referred to as a voltage terminal, and may generally mean a common node or set of coupled nodes in a circuit that are at the same potential.

Claims

1. A circuit comprising: a first transistor having a control terminal and a first terminal and a second terminal, a first capacitor having a first terminal and a second terminal, the first terminal of the first capacitor being coupled to the control terminal of the first transistor and the second terminal of the first capacitor being coupled to the second terminal of the first transistor; a first switch having a first terminal and a second terminal, the second terminal of the first switch being coupled to the control terminal of the first transistor; as well as A second capacitor has a first terminal and a second terminal, the first terminal of the second capacitor being coupled to the first terminal of the first transistor and the second terminal of the second capacitor being coupled to the first terminal of the first switch.

2. The circuit according to claim 1, further comprising: a first resistor having a first terminal and a second terminal, the first terminal of the first resistor being coupled to the second terminal of the first transistor; a second switch having a first terminal and a second terminal, the first terminal of the second switch being coupled to the second terminal of the first resistor; as well as A third capacitor has a first terminal and a second terminal, the first terminal of the third capacitor being coupled to the second terminal of the second switch.

3. The circuit of claim 2, further comprising an audio generating device coupled between the second terminal of the third capacitor and a ground terminal.

4. The circuit according to claim 2, further comprising: an amplifier having an output terminal and a first input terminal and a second input terminal; a third switch having a first terminal and a second terminal, the first terminal of the third switch being coupled to the output terminal of the amplifier and the second terminal of the second switch being coupled to the first terminal of the first switch; as well as 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 capacitor and the second terminal of the second resistor being coupled to a ground terminal.

5. The circuit according to claim 4, further comprising: a second transistor having a control terminal and a first terminal and a second terminal, the first terminal of the second transistor being coupled to the first terminal of the first transistor and the second terminal of the second transistor being coupled to the second terminal of the second switch; a fourth switch having a first terminal and a second terminal, the first terminal of the fourth switch being coupled to the output terminal of the amplifier and the second terminal of the fourth switch being coupled to the control terminal of the second transistor; a third transistor having a control terminal and a first terminal and a second terminal, the first terminal of the third transistor being coupled to the second terminal of the second switch and the second terminal of the third transistor being coupled to the ground terminal; as well as A fifth switch has a first terminal and a second terminal, the first terminal of the fifth switch being coupled to the output terminal of the amplifier and the second terminal of the fifth switch being coupled to the control terminal of the third transistor.

6. The circuit according to claim 5, further comprising: a third resistor having a first terminal and a second terminal, the second terminal of the third resistor being coupled to the second terminal of the first capacitor; a sixth switch having a first terminal and a second terminal, the first terminal of the sixth switch being coupled to the second input terminal of the amplifier and the second terminal of the sixth switch being coupled to the first terminal of the third resistor; a fourth resistor having a first terminal and a second terminal, the second terminal of the fourth resistor being coupled to the second terminal of the second switch; as well as A seventh switch has a first terminal and a second terminal, the first terminal of the seventh switch being coupled to the second input terminal of the amplifier, and the second terminal of the seventh switch being coupled to the first terminal of the fourth resistor.

7. The circuit of claim 1, further comprising a voltage source coupled to the first terminal of the first transistor.

8. A circuit comprising: a first amplifier having an output terminal and a first input terminal and a second input terminal; a first capacitor having a first terminal and a second terminal, the first terminal of the first capacitor being coupled to the second input terminal of the first amplifier; a first switch having a first terminal and a second terminal, the first terminal of the first switch being coupled to the first terminal of the first capacitor; as well as A second capacitor has a first terminal and a second terminal, the first terminal of the second capacitor being coupled to the second terminal of the first switch.

9. The circuit of claim 8, further comprising a second switch having a first terminal and a second terminal, the first terminal of the second switch being coupled to the second terminal of the first switch, wherein the second switch is configured to receive a variable value reference signal at the second terminal of the second switch.

10. The circuit of claim 8, further comprising: a first resistor having a first terminal and a second terminal, the first terminal of the first resistor being coupled to the first input terminal of the first amplifier; a second resistor having a first terminal and a second terminal, the first terminal of the second resistor being coupled to the first input terminal of the first amplifier; as well as A second amplifier has an output terminal and first and second input terminals, the second terminal of the first resistor being coupled to the first input terminal of the second amplifier, and the second terminal of the second resistor being coupled to the second input terminal of the second amplifier.

11. The circuit of claim 10, further comprising: a third resistor having a first terminal and a second terminal, the second terminal of the third resistor being coupled to the output terminal of the second amplifier; a third switch having a first terminal and a second terminal, the first terminal of the third switch being coupled to the first input terminal of the second amplifier, and the second terminal of the third switch being coupled to the said first terminal of a third resistor; a fourth resistor having a first terminal and a second terminal, the first terminal of the fourth resistor being coupled to the second input terminal of the second amplifier; as well as A third amplifier has an output terminal and first and second input terminals, the output terminal of the third amplifier being coupled to the second terminal of the fourth resistor and to the second input terminal of the third amplifier.

12. The circuit of claim 10, further comprising: a third resistor having a first terminal and a second terminal, the first terminal of the third resistor being coupled to the output terminal of the first amplifier; a fourth resistor having a first terminal and a second terminal, the first terminal of the fourth resistor being coupled to the output terminal of the first amplifier; as well as A chopper circuit having first and second input terminals and first and second output terminals, the first input terminal being coupled to the second terminal of the third resistor, the first output terminal being coupled to the first input terminal of the second amplifier, the second input terminal being coupled to the second terminal of the fourth resistor, and the second output terminal being coupled to the second input terminal of the second amplifier.

13. The circuit of claim 12, further comprising a third capacitor having a first terminal and a second terminal, the first terminal of the third capacitor coupled to the output terminal of the second amplifier.

14. A system comprising: A first amplifier having an output terminal and having a first input terminal and a second input terminal, the first amplifier comprising: a first transistor having a control terminal and a first terminal and a second terminal; a first capacitor having a first terminal and a second terminal, the first terminal of the first capacitor being coupled to the control terminal of the first transistor and the second terminal of the first capacitor being coupled to the second terminal of the first transistor; a first switch having a first terminal and a second terminal, the second terminal of the first switch being coupled to the control terminal of the first transistor; and a second capacitor having a first terminal and a second terminal, the first terminal of the second capacitor being coupled to the first terminal of the first transistor and the second terminal of the second capacitor being coupled to the first terminal of the first switch; a second amplifier having an output terminal and a first input terminal and a second input terminal; a third capacitor having a first terminal and a second terminal, the first terminal of the third capacitor being coupled to the second input terminal of the second amplifier; a second switch having a first terminal and a second terminal, the first terminal of the second switch being coupled to the first terminal of the third capacitor; a fourth capacitor having a first terminal and a second terminal, the first terminal of the fourth capacitor being coupled to the second terminal of the second switch; a first resistor having a first terminal and a second terminal, the first terminal of the first resistor being coupled to the first input terminal of the second amplifier and the second terminal of the first resistor being coupled to the first input terminal of the first amplifier; and A second resistor having a first terminal and a second terminal, the first terminal of the second resistor being coupled to the first input terminal of the second amplifier, and the second terminal of the second resistor being coupled to the second input terminal of the first amplifier.

15. The system according to claim 14, comprising: A third switch has a first terminal and a second terminal, the first terminal of the third switch being coupled to the second terminal of the second switch, wherein the third switch is configured to receive a variable value reference signal at the second terminal of the third switch.

16. The system of claim 14, comprising a controller coupled to the first switch and the second switch.

17. The system of claim 14, comprising: a third resistor having a first terminal and a second terminal, the first terminal of the third resistor being coupled to the output terminal of the second amplifier; a fourth resistor having a first terminal and a second terminal, the first terminal of the fourth resistor being coupled to the output terminal of the second amplifier; as well as A chopper circuit having first and second input terminals and first and second output terminals, the first input terminal being coupled to the second terminal of the third resistor, the first output terminal being coupled to the first input terminal of the first amplifier, the second input terminal being coupled to the second terminal of the fourth resistor, and the second output terminal being coupled to the second input terminal of the first amplifier.

18. The system of claim 14, comprising: a third resistor having a first terminal and a second terminal, the second terminal of the third resistor being coupled to the output terminal of the first amplifier; a third switch having a first terminal and a second terminal, the first terminal of the third switch being coupled to the first input terminal of the first amplifier, and the second terminal of the third switch being coupled to the said first terminal of a third resistor; a fourth resistor having a first terminal and a second terminal, the first terminal of the fourth resistor being coupled to the second input terminal of the first amplifier; as well as A third amplifier has an output terminal and first and second input terminals, the output terminal of the third amplifier being coupled to the second terminal of the fourth resistor and to the second input terminal of the third amplifier.

19. The system of claim 14, wherein the first amplifier comprises: 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 first transistor; a third switch having a first terminal and a second terminal, the first terminal of the third switch being coupled to the second terminal of the third resistor; as well as a third capacitor having a first terminal and a second terminal, the first terminal of the third capacitor being coupled to the second terminal of the third switch; a third amplifier having an output terminal and a first input terminal and a second input terminal; a fourth switch having a first terminal and a second terminal, the first terminal of the third switch being coupled to the output terminal of the third amplifier and the second terminal of the fourth switch being coupled to the first terminal of the first switch; 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 first capacitor and the second terminal of the fourth resistor being coupled to a ground terminal; a second transistor having a control terminal and a first terminal and a second terminal, the first terminal of the second transistor being coupled to the first terminal of the first transistor and the second terminal of the second transistor being coupled to the second terminal of the third switch; a fifth switch having a first terminal and a second terminal, the first terminal of the fifth switch being coupled to the output terminal of the third amplifier and the second terminal of the fifth switch being coupled to the control terminal of the second transistor; a third transistor having a control terminal and a first terminal and a second terminal, the first terminal of the third transistor being coupled to the second terminal of the second switch and the second terminal of the third transistor being coupled to the ground terminal; as well as A sixth switch has a first terminal and a second terminal, the first terminal of the sixth switch being coupled to the output terminal of the third amplifier and the second terminal of the sixth switch being coupled to the control terminal of the third transistor.

20. The system of claim 14, comprising a fifth capacitor having a first terminal and a second terminal, the first terminal of the fifth capacitor coupled to the output terminal of the first amplifier.

Images