Capacitive feedback type current detection amplifier circuit
By adding a switch and a capacitor to the current sensing amplifier circuit, the problem of random sampling values caused by thermal noise of the reset switch's on-resistance was solved, achieving effective noise compensation without changing the process and voltage withstand parameters, thus improving the circuit's accuracy.
Patent Information
- Application Number
- CN202510811568.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-17
- Publication Date
- 2025-10-28
AI Technical Summary
In existing capacitive feedback current sensing amplifiers, the thermal noise of the on-resistance of the reset switch generates random sampling values at the moment the switch is turned off, leading to detection errors and affecting the accuracy of high-precision photoelectric sensors. Furthermore, existing methods, such as increasing the overdrive voltage or using low-impedance materials, are difficult to apply in silicon-based processes.
By adding a switch and a capacitor to the current sensing amplifier circuit, the noise's influence on the circuit can be suppressed by storing the random sampled noise values on the capacitor and then inverting them to compensate for the circuit's output or intermediate nodes.
Without changing the process and voltage withstand parameters, the noise-sensitive sampling circuit was significantly optimized, reducing random fluctuations in the output voltage and improving detection accuracy.
Smart Images
Figure CN120856065A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a capacitor feedback type current detection amplifier circuit, belonging to the field of electronic device technology. Background Technology
[0002] Correlated Double Sampling (CDS) is a key technique for reducing readout noise. For example, a sample is taken once in the reset state, and then a second sample is taken after the signal is received. The difference between the two samples gives the signal contribution value.
[0003] The thermal noise on the on-resistance of the MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) used as a reset switch is not the offset at the moment of switch turn-off, and the random sampled value of the thermal noise at the moment of switch turn-off cannot be obtained by sampling the reset device. Therefore, conventional correlated double sampling cannot eliminate the influence of random transient values of thermal noise.
[0004] The readout circuit of a photoelectric sensor is usually designed as a capacitive feedback current sensing amplifier to convert the current signal of the photoelectric sensor into a voltage signal that is easy to quantize. Figure 1 This is the circuit schematic of an existing capacitor feedback type current sense amplifier. Figure 2 for Figure 1 The equivalent circuit diagram of the medium current sensing amplifier when the reset switch is on is shown below. Figure 1 As shown, connected in parallel with the feedback capacitor Cfb is an analog switch (reset switch) used for reset. When the reset switch is on, the readout circuit is in a reset state. Theoretically, the voltage at the output of the operational amplifier should be equal to the voltage at its inverting input. However, due to the thermal noise of the reset switch's on-resistance Rsw, the voltage at the output of the operational amplifier will deviate slightly from the voltage at its inverting input. Figure 2 As shown, at the moment the reset switch opens after the reset is complete, it is equivalent to sampling the thermal noise. The sampled value is stored at the output of the operational amplifier as a random voltage difference within a thermal noise fluctuation range, introducing a random detection error. This is equivalent to a random offset in the detector circuit, which is different for each detection operation and cannot be predicted. For high-precision photoelectric sensor readout circuits, this offset will seriously affect the detector's accuracy and needs to be minimized as much as possible.
[0005] Based on the formulas for calculating the thermal noise of resistors and the on-resistance of MOSFETs, reducing the on-resistance of the reset switch can decrease the magnitude of the resistor's thermal noise. For example, the on-resistance of the MOSFET can be reduced by increasing the overdrive voltage Vgs-Vth when the MOSFET is turned on. However, the effective value of the thermal noise voltage is only inversely proportional to the square root of the overdrive voltage. Therefore, the efficiency of reducing the effective value of the thermal noise voltage by increasing the overdrive voltage is limited. In addition, the overdrive voltage cannot be increased excessively due to the voltage withstand capability limitations of the circuit devices. On the other hand, although using low-impedance materials (such as gallium nitride, which has low impedance) to fabricate the reset switch can reduce the thermal noise of the on-resistance, this method is not universally applicable and is more suitable for the manufacture of power devices, making it difficult to apply to the design of the most commonly used silicon-based analog-to-digital chips. Summary of the Invention
[0006] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a capacitor feedback current sensing amplifier circuit. By adding a switch and a capacitor to the current sensing amplifier circuit, without changing the process and voltage withstand parameters, the random noise sampling value can be stored on the capacitor, and the random noise sampling value stored on the capacitor can be inverted and compensated to the output terminal or intermediate node of the circuit, thereby suppressing the influence of the random noise sampling value on the circuit. This invention has a significant optimization effect on noise-sensitive sampling circuits.
[0007] The technical problem to be solved by the present invention is achieved through the following technical solution:
[0008] This invention provides a capacitor feedback type current detection amplifier circuit, including an operational amplifier, a feedback capacitor, a load capacitor, a reset switch, a first capacitor, a second capacitor, a first switching switch, and a second switching switch.
[0009] Wherein, the inverting input terminal of the operational amplifier is connected to the first terminal of the feedback capacitor and the first terminal of the second capacitor, the reference voltage is input to the non-inverting input terminal of the operational amplifier, the output terminal of the operational amplifier is connected to the second terminal of the feedback capacitor and the first terminal of the load capacitor, the reset switch is connected in parallel with the feedback capacitor, the second terminal of the load capacitor is grounded, and the second terminal of the first capacitor is grounded;
[0010] The second terminal of the second capacitor is selectively connected to the non-inverting input terminal of the operational amplifier or the first switching switch via the second switching switch, and the first terminal of the first capacitor is selectively connected to the output terminal of the operational amplifier or the second switching switch via the first switching switch.
[0011] Preferably, in the first operating state, the first terminal of the first switching switch is connected to the output terminal of the operational amplifier, and the second terminal of the second switching switch is connected to the non-inverting input terminal of the operational amplifier; in the second operating state, the first terminal of the first switching switch is connected to the second terminal of the second switching switch.
[0012] Preferably, the first capacitor has the same capacitance value as the load capacitor, and the second capacitor has the same capacitance value as the feedback capacitor.
[0013] In summary, this invention, by adding a switch and a capacitor to the current sensing amplifier circuit, can store random noise sampling values on the capacitor without changing the process and voltage withstand parameters. Furthermore, the random noise sampling values stored on the capacitor are inverted and compensated to the output or intermediate node of the circuit, thereby suppressing the influence of random noise sampling values on the circuit. This invention has a significant optimization effect on noise-sensitive sampling circuits.
[0014] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description
[0015] Figure 1 The circuit schematic of an existing capacitor feedback current sensing amplifier is shown.
[0016] Figure 2 for Figure 1 Equivalent circuit diagram of the medium current sensing amplifier when the reset switch is turned on;
[0017] Figure 3 This is a circuit state diagram of the capacitor feedback current detection amplifier circuit of the present invention when the reset switch is turned on and when it is turned off;
[0018] Figure 4 This is a circuit state diagram of the capacitor feedback current detection amplifier circuit of the present invention when compensating for thermal noise sampling values.
[0019] Figure 5 Comparison of Monte Carlo simulation waveforms with and without compensation;
[0020] Figure 6 This is a comparison chart of the statistical results of Monte Carlo simulations with and without compensation. Detailed Implementation
[0021] In current sense amplifier design, thermal noise is generated in the on-resistance when the reset switch is on. At the instant the reset switch is off, this thermal noise is sampled as a random value within its disturbance range. While this random value is acceptable in low-precision designs, in high-precision current sense amplifiers, even a small amount of random noise can significantly affect the output voltage. This invention provides a capacitor feedback current sense amplifier circuit that compensates for the influence of the random instantaneous value of the thermal noise from the reset switch's on-resistance during sampling, without changing the process and voltage withstand parameters.
[0022] Figure 3 This is a circuit state diagram of the capacitor feedback current detection amplifier circuit of the present invention when the reset switch is turned on and when it is turned off; Figure 4 This is a circuit state diagram of the capacitor feedback current detection amplifier circuit of the present invention when compensating for thermal noise sampling values. Figure 3 and Figure 4 As shown, this invention provides a capacitor feedback current sensing amplifier circuit, including an operational amplifier, a feedback capacitor Cfb, a load capacitor CL, a reset switch (not shown in the figure), a first capacitor C1, a second capacitor C2, a first switching switch S1, and a second switching switch S2. This invention compensates for the random sampling values of the thermal noise of the reset switch through a switched capacitor circuit. Compared with existing capacitor feedback current sensing amplifiers, it adds a first capacitor C1, a second capacitor C2, a first switching switch S1, and a second switching switch S2. The structure of existing capacitor feedback current sensing amplifiers is prior art and will not be described further here.
[0023] In this embodiment, the inverting input of the operational amplifier is connected to the first terminal of the feedback capacitor Cfb and the first terminal of the second capacitor C2. The reference voltage VREF is input to the non-inverting input of the operational amplifier. The output of the operational amplifier is connected to the second terminal of the feedback capacitor Cfb and the first terminal of the load capacitor CL. The reset switch is connected in parallel with the feedback capacitor Cfb. The second terminal of the load capacitor CL is grounded.
[0024] The second terminal of the second capacitor C2 is selectively connected to the non-inverting input terminal of the operational amplifier or the first switching switch S1 via the second switching switch S2. The first terminal of the first capacitor C1 is selectively connected to the output terminal of the operational amplifier or the second switching switch S2 via the first switching switch S1. The second terminal of the first capacitor C1 is grounded.
[0025] In other words, the first end of the second switch S2 is connected to the second end of the second capacitor C2, and the second end of the second switch S2 can be connected to the non-inverting input of the operational amplifier or to the first end of the first switch S1; the first end of the first switch S1 can be connected to the output of the operational amplifier or to the second end of the second switch S2, and the second end of the first switch S1 is connected to the first end of the first capacitor C1.
[0026] Preferably, the capacitance value of the first capacitor C1 is equal to that of the load capacitor CL, and the capacitance value of the second capacitor C2 is equal to that of the feedback capacitor Cfb. This invention is not limited to this; any capacitor can store the required random noise value for compensation. For example, when the capacitance values of the first capacitor C1 and the load capacitor CL are equal, and the capacitance values of the second capacitor C2 and the feedback capacitor Cfb are equal, the required random noise value for compensation is stored on the capacitor at its original value. By changing the values of the first capacitor C1 and / or the second capacitor C2, the required random noise value for compensation can be stored proportionally on the capacitor to meet different needs.
[0027] Figure 3 The circuit states of a capacitor feedback current sense amplifier circuit are shown when the reset switch is on and when it is off, such as... Figure 3 As shown, at this time, the first switch S1 and the second switch S2 are in the first working state. Specifically, the first end of the first switch S1 is connected to the output end of the operational amplifier, and the second end of the second switch S2 is connected to the non-inverting input end of the operational amplifier.
[0028] At this time, the first capacitor C1 is connected in parallel with the load capacitor CL. The first end of the first capacitor C1 (e.g., the upper plate) is connected to the output of the operational amplifier via the first switching switch S1. The first capacitor C1 and the load capacitor CL together sample and hold the thermal noise of the on-resistance of the reset switch when the reset switch is open. The magnitude of the voltage deviation from the theoretical potential is Δv.
[0029] After the reset switch is disconnected and the sampled random thermal noise value stabilizes, connect the first terminal of the first switch S1 to the second terminal of the second switch S2, so that the first switch S1 and the second switch S2 are in the second working state, such as... Figure 4 As shown, the first capacitor C1 and the second capacitor C2 are connected in series. At this time, the voltage across the second capacitor C2 is VI=VREF. The first terminal (upper plate) of the first capacitor C1 with a voltage of VI+Δv is connected to the second terminal (e.g., the right plate) of the second capacitor C2 with a voltage of VI, causing capacitor C2 to start charging (discharging).
[0030] When Δv > 0, the voltage at the second terminal of the second capacitor C2 is higher than that at the first terminal (e.g., the voltage at the right plate is higher than that at the left plate). Positive charges will flow out of the left plate. Due to the virtual open circuit characteristic of the operational amplifier, the current flowing out of the left plate of the second capacitor C2 flows into the first terminal (e.g., the left plate) of the feedback capacitor Cfb, causing a voltage drop at the second terminal (e.g., the right plate) of the feedback capacitor Cfb. Since the capacitance values of the second capacitor C2 and the feedback capacitor Cfb are equal (C2 = Cfb), the voltage drop at the right plate of the feedback capacitor Cfb, i.e., the output terminal, is Δv, which precisely compensates for the voltage increase at the output terminal caused by the random sampling of thermal noise. Similarly, when Δv < 0, the capacitor feedback current detection amplifier circuit in this invention can also compensate for the voltage drop at the output terminal.
[0031] Since the load capacitor CL usually has a large capacitance value, the natural discharge speed of the first capacitor C1 and the second capacitor C2 in series is much lower than the signal detection speed of the current detection amplifier. In addition, considering that the sample-and-hold circuit connected after the current detection amplifier can shield other influences after receiving the signal, it is not necessary to reset the first switching switch S1 and the second switching switch S2 after the charge compensation is completed. They can be reset together with the detector circuit after the single signal sampling and conversion is completed, which greatly simplifies the complexity of the control circuit and the strictness of the timing requirements.
[0032] The present invention aims to reduce the influence of random sampling values of thermal noise. Therefore, it is necessary to observe the effect of this method under the condition of introducing device noise, so Monte Carlo analysis is suitable.
[0033] Under identical circuit and other conditions, the two operations with and without compensation (i.e., with and without compensation) are compared. Figure 1 The circuit of the capacitor feedback current sensing amplifier was analyzed using two configurations: one with the addition of a first switching switch S1 and a second switching switch S2, and the other with the addition of a first capacitor C1 and a second capacitor C2. 300 Monte Carlo simulations were performed on each configuration, and the effective voltage value at the output of the current sensing amplifier was recorded for each simulation. The waveform results are shown below. Figure 5 As shown, Figure 5 The diagram shows a comparison of Monte Carlo simulation waveforms with and without compensation.
[0034] Figure 5 The waveform at the top center is the simulated waveform with compensation, while the waveform at the bottom is the simulated waveform without compensation. Figure 5 It is evident that after the compensation operation, the waveform of the 300 random noises is compressed more compactly, and the difference in the influence of different thermal noise sampling values is significantly reduced.
[0035] Statistical analysis was performed on the results of the 300 Monte Carlo simulations, including the distribution of the effective value of the current sensing amplifier's output voltage and statistical parameters. Figure 6 As shown, Figure 6 The comparison of Monte Carlo simulation statistics with and without compensation is shown.
[0036] Figure 6 The top center shows the RMS output voltage distribution with compensation, while the bottom center shows the RMS output voltage distribution without compensation. A comparison clearly shows that with compensation, the RMS output voltage distribution is highly concentrated, with a much smaller dispersion than without compensation. With compensation, the standard deviation of the RMS output voltage is 0.852 mV, while without compensation, the standard deviation is as high as 4.06 mV. These quantitative statistical parameters demonstrate the significant effect of compensation.
[0037] It should be added that the present invention is applicable to the compensation of random noise sampling values, which can be thermal noise or other noise; it can be the random noise value sampled when the reset switch is opened, or other random noise values sampled when the circuit enters a locked state.
[0038] In summary, this invention, by adding a switch and a capacitor to the current sensing amplifier circuit, can store random noise sampling values on the capacitor without changing the process and voltage withstand parameters. Furthermore, the random noise sampling values stored on the capacitor are inverted and compensated to the output or intermediate node of the circuit, thereby suppressing the influence of random noise sampling values on the circuit. This invention has a significant optimization effect on noise-sensitive sampling circuits.
Claims
1. A capacitor feedback type current detection amplifier circuit, characterized in that, This includes an operational amplifier, a feedback capacitor, a load capacitor, a reset switch, a first capacitor, a second capacitor, a first switching switch, and a second switching switch. Wherein, the inverting input terminal of the operational amplifier is connected to the first terminal of the feedback capacitor and the first terminal of the second capacitor, the reference voltage is input to the non-inverting input terminal of the operational amplifier, the output terminal of the operational amplifier is connected to the second terminal of the feedback capacitor and the first terminal of the load capacitor, the reset switch is connected in parallel with the feedback capacitor, the second terminal of the load capacitor is grounded, and the second terminal of the first capacitor is grounded; The second terminal of the second capacitor is selectively connected to the non-inverting input terminal of the operational amplifier or the first switching switch via the second switching switch, and the first terminal of the first capacitor is selectively connected to the output terminal of the operational amplifier or the second switching switch via the first switching switch.
2. The capacitor feedback type current detection amplifier circuit as described in claim 1, characterized in that, In the first operating state, the first terminal of the first switching switch is connected to the output terminal of the operational amplifier, and the second terminal of the second switching switch is connected to the non-inverting input terminal of the operational amplifier; in the second operating state, the first terminal of the first switching switch is connected to the second terminal of the second switching switch.
3. The capacitor feedback type current detection amplifier circuit as described in claim 2, characterized in that, The first capacitor has the same capacitance value as the load capacitor, and the second capacitor has the same capacitance value as the feedback capacitor.