Trans-impedance amplifier with low offset voltage

Abstract

The invention provides a single-ended output trans-impedance amplifier circuit with low offset voltage. The low-offset single-ended output transimpedance amplifier circuit is characterized in that the low-offset single-ended output transimpedance amplifier circuit is composed of a pre-stage transimpedance amplifier (1), a post-stage amplification circuit (2) and an output signal detection circuit (3), wherein the output signal detection circuit (3) is composed of a valley value detection circuit composed of an EA1 (31) and a D1 (33), a peak value detection circuit composed of an EA2 (32) and a D2 (34), a diode (35) and a capacitor (36). The device can be used for measuring extremely weak current, and can be widely applied to the fields of sensor signal processing, photoelectric detection, optical communication, biomedical engineering and the like.

Description

(I) Technical field

[0001] The invention relates to a single-ended output transimpedance amplifier circuit with low offset voltage, which can be used for sensor signal processing, photoelectric detection, optical communication, current signal detection in biomedical engineering, etc., and belongs to the field of electronic technology. (II) Background technology

[0002] The trans-impedance amplifier (TIA) circuit is a current-to-voltage conversion circuit. The principle is to convert current into voltage through a feedback circuit, and obtain an amplified voltage output at the output end to achieve IV conversion. It is the core of weak current measurement such as sensor signal processing, photoelectric detection, optical communication, and bioelectric signal processing. The trans-impedance amplifier is usually connected to the output end of the sensor. The sensor (such as a photodiode) is used to sense the characteristic parameters of the detected object or environment, and outputs a current signal corresponding to the sensed signal. The current signal output by the sensor is amplified to the required voltage level, so that the signal output by the sensor can be effectively processed and transmitted. With the advancement of semiconductor process technology and the improvement of integrated circuit design level, from an economic point of view, CMOS is the preferred technology for designing analog circuits because it is relatively low in cost and can integrate low-power digital signal processing, which makes the realization of complex mixed signal systems possible and has broad application prospects.

[0003] However, typical CMOS amplifiers have deviations due to various factors in the manufacturing process, resulting in an input offset voltage that is usually in the millivolt range. This offset voltage will also be amplified to the output end and input to the subsequent circuit for further amplification, causing the output static voltage to deviate from the reference voltage. When the deviation is large enough, it will cause misjudgment of the subsequent signal processing circuit, severely limiting the accuracy of the amplifier. Therefore, the demand for precision electronic devices is to continuously strive to reduce the offset voltage of the amplifier.

[0004] There are two commonly used offset elimination techniques, auto-zeroing and chopping. Auto-zeroing is a sampling technique that measures the offset in one stage and subtracts it in another stage, but it is difficult to apply to continuous-time amplifiers. On the other hand, chopping is a frequency modulation technique that modulates the signal and offset to different frequencies and then filters them out, but it is difficult to apply to high-frequency signals. The combination of the two requires multiple switches and capacitors, sacrificing a lot of circuit area while introducing new noise and offset, which is not suitable for TIAs used as front-end readout circuits. Therefore, other techniques are needed to eliminate the offset voltage in TIAs used at high operating frequencies.

[0005] In order to eliminate the offset voltage of TIA, researchers designed TIA circuits with different structures in different standard integrated circuit processes to reduce the offset voltage and improve the accuracy of the detection circuit. For example, in 2010, T.Takemoto et al. used an RC filter circuit to obtain the common-mode voltage in the TIA circuit prepared at 65nm process, and fed it back to the input end for offset elimination (T.Takemoto, et al., "A compact 4X 25-Gb / s 3.0mW / Gb / s CMOS-based optical receiver for board-to-board interconnects," J.Lightw.Tech., vol.28, pp.3343–3350, 2010.). In the following years, his team improved the TIA circuit by introducing a programmable voltage in the feedforward circuit to compensate for the offset voltage of the first-stage amplifier. The RC filter circuit was still used in the subsequent stage, which could reduce the capacitance used in the RC filter circuit to reduce the circuit area (T.Takemoto, et al., "A 25-to-28Gb / s high-sensitivity (-9.7dBm) 65nm CMOS optical receiver for board-to-boardinterconnects," IEEE Transactions on Optoelectronics, vol. 28, pp.3343–3350, 2010.). J.Solid-State Circuits, vol.49, no.10, pp.2259–2276, Oct.2014.); and B.Sedighi and J.C.Scheytt first subtract the positive and negative ends of the output voltage, then use RC filtering after the integration circuit to obtain the common-mode voltage, and then feed it back to the input end to eliminate the offset (B.Sedighi and J.C.Scheytt, "Low-power SiGe BiCMOS tran-simpedance amplifier for 25-GBaud optical links," IEEE Trans.Circuits Syst. II: Express Briefs, vol.59, no.8, pp.461–465, Aug.2012.). By feeding the common-mode voltage back to the input end to eliminate the offset, the offset voltage of the TIA output is significantly reduced. However, a careful analysis shows that these technical means essentially use RC filtering to process differential signals and cannot be directly applied to single-ended output TIA circuits. This is because the essence of RC filtering is integration. If RC filtering is used on a single-ended output circuit, the resulting voltage is a value related to the output amplitude and frequency.In addition, Tao Jingjing et al. disclosed "A TIA input offset voltage calibration method and calibration circuit" (Chinese patent: 202411509261.6) in May 2024, using a comparator, calibration algorithm, load output stage and calibration output stage, and using an algorithm to control the output of the two output stages to reduce the offset voltage; Zhang Chaoxuan et al. disclosed "A high-integration, low DC offset, high-bandwidth precision transimpedance amplifier" (Chinese patent: 202311559448.2) in March 2024, quantizing the output voltage through a quantizer, controlling the feedback network and input current compensation, and reducing the offset voltage. The defects of these designs are: 1. The described circuit can still only be used in a dual-ended output TIA circuit. For applications that require a single-ended output TIA, such as photon counting, sensor interface, reset control signal, etc., this method cannot be used to reduce the offset voltage, resulting in system detection errors; 2. The described circuit requires a complex control module, which occupies a large amount of circuit area. For example, the calibration algorithm usually needs to be specially designed for circuits of different applications, which greatly increases the size and complexity of the TIA circuit; the quantizer requires a large number of sampling circuits and switches, which introduces additional noise while reducing the detection efficiency of the circuit, causing system errors.

[0006] In order to solve the above problems, the present invention discloses a single-ended output transimpedance amplifier circuit with low offset voltage, which can be used for sensor signal processing, photoelectric detection, optical communication, and current signal detection in biomedical engineering. The present invention replaces the RC low-pass filter in the commonly used offset elimination circuit with an output voltage signal detection circuit that can obtain the maximum and minimum values ​​of the output voltage, which can be directly applied to the TIA circuit with single-ended output, eliminating the process and required circuit of converting to a differential signal first, eliminating the offset, and then converting back to a single-ended signal. When the circuit is powered on and stable, the output signal detection circuit can obtain the peak and valley values ​​of the output voltage, and the valley voltage is the output voltage in static state, and this voltage is fed back to a negative input terminal of the TIA. When the circuit is offset and causes the output static voltage to shift, the offset voltage at the output terminal is eliminated through this negative feedback mechanism, so that the output static voltage is closer to the reference voltage of the positive input terminal of the TIA, thereby improving the accuracy of the detection circuit. In addition, in addition to powering on the valley detection circuit, the peak detection circuit can also be used as a control signal after processing to control parameters such as the gain of the TIA. (III) Summary of the invention

[0007] The object of the present invention is to provide a low offset single-ended transimpedance amplifier circuit consisting of a front-stage transimpedance amplifier 1, a post-stage amplifier circuit 2, and an output signal detection circuit 3, wherein the output signal detection circuit 3 consists of a valley detection circuit composed of 31 and 33, a peak detection circuit composed of 32 and 34, a diode 35 and a capacitor 36.

[0008] The object of the present invention is achieved in that:

[0009] The front-stage transimpedance amplifier 1 operates under a given bias voltage and reference voltage, converts the input current signal into a voltage signal and amplifies it to achieve transimpedance amplification. The rear-stage amplifier circuit 2 uses the same reference voltage as the front-stage transimpedance amplifier 1 to further amplify the voltage signal output by the front-stage transimpedance amplifier 1. The error amplifier 31 and the diode 33 in the output signal detection circuit 3 constitute a valley detection circuit, which can obtain the minimum value of the output voltage signal on the capacitor 36. The error amplifier 32 and the diode 34 constitute a peak detection circuit, which can obtain the maximum value of the output voltage signal at the anode of the diode 35. When powered on, the error amplifier 32 outputs a high voltage, and the capacitor 36 is charged through the diodes 34 and 35. When the voltage on the capacitor 36 is greater than the output voltage signal, the error amplifier 31 outputs a low voltage to start the valley detection circuit, and the minimum value of the output voltage signal (i.e., the static voltage) can be obtained, and used as the offset elimination control voltage V DCOC Connected to the negative input terminal of the compensation input in the front-stage transimpedance amplifier 1, when the circuit has an offset causing the output static voltage to deviate from the reference voltage, compensation is performed through negative feedback to reduce the output offset voltage, and finally an output voltage signal with the offset voltage reduced is obtained. (Further details and explanations are given below, including other claims and their details)

[0010] The front-stage transimpedance amplifier 1 in the circuit can be one of various transimpedance amplifiers such as a feedback structure TIA with a compensation input, a common-gate structure TIA, a regulated common-gate structure TIA, or a TIA with a current amplifier. The input current of the front-stage transimpedance amplifier 1 in the circuit can be one of various current signals such as a current signal output by a photoelectric sensor such as a photodiode or a phototransistor, a bioelectric signal, etc.

[0011] The post-stage amplifier circuit 2 in the circuit is an amplifier circuit that outputs an in-phase proportional amplification voltage, and can be composed of discrete devices or integrated circuits. Its manufacturing process can be any one of integrated circuit processes such as bipolar transistor process (BJT), standard complementary metal oxide semiconductor process (CMOS), bipolar complementary metal oxide semiconductor process (BiCMOS), gallium arsenide semiconductor process (GaAs), silicon germanium semiconductor process (SiGe) and silicon crystal insulator complementary metal oxide semiconductor process (SOI CMOS). The post-stage amplifier circuit 2 can be obtained by cascading multiple in-phase proportional amplifier circuits, or by cascading an even number of reverse proportional amplifier circuits. Its function is to amplify the output voltage of the previous transimpedance amplifier 1 again to improve the overall transimpedance gain of the circuit.

[0012] The output signal detection circuit 3 can be composed of discrete devices or integrated circuits. The diodes 33, 34, and 35 can be any structure that can achieve unidirectional conduction characteristics, such as PN junctions, bipolar transistors with base and collector shorted, or field effect transistors with gate and drain shorted. The main function of the output signal detection circuit 3 is to obtain the minimum value of the output voltage, which is achieved by the valley detection circuits 31 and 33. The valley detection circuit needs to be charged by the startup circuit when it is powered on, which is achieved by the peak detection circuits 32 and 34 coupled through the diode 35.

[0013] At the initial moment of circuit power-on, the output voltage is high, the voltages at both ends of diode 35 are low, the error amplifier 32 outputs a high voltage, and the capacitor 36 is charged through diodes 34 and 35, V DCOC After negative feedback, the output voltage decreases, the error amplifier 32 outputs a low voltage, the diode 34 is turned off, and the residual voltage at its cathode continues to charge the capacitor 36. DCOC The output voltage continues to decrease until V DCOC When the output voltage is equal to the minimum value, V DCOC The error amplifier 31 outputs a low voltage, the diode 33 is turned on, the capacitor 36 is discharged, and V DCOC The cathode voltage of the diode 34 also decreases during the process. When it is lower than the maximum value of the output voltage, the error amplifier 32 outputs a high voltage, the diode 34 is turned on again, and the cathode voltage increases. Therefore, when the circuit is relatively stable, the voltage on the capacitor 36 fluctuates around the minimum value of the output voltage, and the cathode voltage of the diode 34 fluctuates around the maximum value of the output voltage. Thus, the maximum and minimum values ​​of the output voltage can be obtained, that is, it can be used as a peak detection circuit and a valley detection circuit. (IV) Description of the drawings

[0014] Figure 1 The schematic diagram of the structure of a single-ended output transimpedance amplifier circuit with low offset voltage is shown in FIG. The low offset single-ended transimpedance amplifier circuit is composed of a front-stage transimpedance amplifier 1, a rear-stage amplifier circuit 2, and an output signal detection circuit 3, wherein the output signal detection circuit 3 is composed of a valley detection circuit composed of 31 and 33, a peak detection circuit composed of 32 and 34, a diode 35, and a capacitor 36.

[0015] Figure 2: is a schematic diagram of an embodiment of a single-ended output transimpedance amplifier circuit with low offset voltage. The low offset single-ended transimpedance amplifier circuit is composed of a front-stage transimpedance amplifier 1, a post-stage amplifier circuit 2, and an output signal detection circuit 3, wherein the front-stage transimpedance amplifier 1 is composed of a main input differential pair 11, a compensation input differential pair 12, an input stage load 13, a current mirror 14, a second-stage input 15, a transimpedance feedback network 16, and a Miller compensation circuit 17. In the circuit, the main input differential pair 11 and the compensation input differential pair 12 of the front-stage transimpedance amplifier 1 are composed of four MOS tubes with equal width-to-length ratios, and the tail currents of the two differential pairs are also equal, and the same set of input stage loads 13 are used. When the circuit offset causes the output static voltage to deviate from the reference voltage, it is equivalent to an input offset voltage between the positive and negative input terminals of the ideal TIA at the input terminal of the TIA. Therefore, the output static voltage V DCOC The feedback is fed back to the negative end of the compensation input differential pair 12, so that the output static voltage adjusts the TIA input stage and compensates for the current of the input stage load.

[0016] Figure 3 It is a structural diagram of a post-stage amplifier circuit composed of a reverse proportional amplifier circuit. (V) Specific implementation methods

[0017] The present invention will be further described below in conjunction with specific embodiments.

[0018] Figure 2 An embodiment of a single-ended output transimpedance amplifier circuit with low offset voltage is given. The low offset single-ended transimpedance amplifier circuit is composed of a front-stage transimpedance amplifier 1, a rear-stage amplifier circuit 2, and an output signal detection circuit 3, wherein the front-stage transimpedance amplifier 1 uses a feedback structure TIA with a compensation input, and is composed of a main input differential pair 11, a compensation input differential pair 12, an input stage load 13, a current mirror 14, a second-stage input 15, a transimpedance feedback network 16, and a Miller compensation circuit 17.

[0019] The input current of the front-stage transimpedance amplifier 1 can be a current signal output by a photoelectric sensor such as a photodiode or a phototransistor, a bioelectric signal or other current signal. The rear-stage amplifier circuit 2 uses the same reference voltage as the front-stage transimpedance amplifier 1 to further amplify the voltage signal output by the front-stage transimpedance amplifier 1. The output signal detection circuit 3 uses the following Figure 1 The circuit structure shown and described in the figure consists of a valley detection circuit, a peak detection circuit, a diode and a capacitor.

[0020] At the initial moment of circuit power-on, the output voltage is high, the voltages at both ends of diode 35 are low, the error amplifier 32 outputs a high voltage, and the capacitor 36 is charged through diodes 34 and 35, V DCOCAfter negative feedback, the output voltage decreases, the error amplifier 32 outputs a low voltage, the diode 34 is turned off, and the residual voltage at its cathode continues to charge the capacitor 36. DCOC The output voltage continues to decrease until V DCOC When the output voltage is equal to the minimum value, V DCOC The error amplifier 31 outputs a low voltage, the diode 33 is turned on, the capacitor 36 is discharged, and V DCOC The cathode voltage of diode 34 also decreases during the process. When it is lower than the maximum value of the output voltage, the error amplifier 32 outputs a high voltage, the diode 34 is turned on again, and the cathode voltage increases. Therefore, when the circuit is relatively stable, the voltage on capacitor 36 fluctuates around the minimum value of the output voltage, and the cathode voltage of diode 34 fluctuates around the maximum value of the output voltage. Thus, the maximum and minimum values ​​of the output voltage can be obtained, that is, it can be used as a peak detection circuit and a valley detection circuit. The voltage V DCOC This is the minimum value of the output voltage.

[0021] The main input differential pair 11 and the compensation input differential pair 12 of the front-stage transimpedance amplifier 1 in the circuit are composed of four MOS tubes with equal width-to-length ratios. The tail currents of the two differential pairs are also equal, and the positive input terminals are both connected to the reference voltage, and the same set of input stage loads 13 are used. When the compensation input differential pair is not used, the quiescent currents of the input stage loads should be equal in an ideal state. However, due to deviations caused by various factors in the manufacturing process, the quiescent currents on both sides are not equal, the output quiescent voltage is offset, and the post-stage amplifier circuit is also offset. Therefore, after amplification by the post-stage amplifier circuit, the output quiescent voltage V DCOC With reference voltage V R There is a large deviation.

[0022] After adding the compensation input differential pair, the output signal detection circuit 3 is used to obtain the minimum value of the circuit output voltage, that is, the output static voltage V DCOC , and is fed back to the compensation input of the TIA as a control voltage for offset elimination. By compensating the input differential pair 12, the quiescent current of the input stage load 13 is compensated, thereby reducing the offset of the output voltage and improving the accuracy of the detector. It can be widely used in sensor signal processing, photoelectric detection, optical communication, and biomedical engineering.

Claims

1. A single-ended output transimpedance amplifier circuit with low offset voltage. Its characteristics are: The low offset single-ended transimpedance amplifier circuit is composed of a front-stage transimpedance amplifier (1), a rear-stage amplifier circuit (2), and an output signal detection circuit (3), wherein the output signal detection circuit (3) is composed of a valley detection circuit composed of EA1 (31) and D1 (33), a peak detection circuit composed of EA2 (32) and D2 (34), a diode (35), and a capacitor (36); in the system, the front-stage transimpedance amplifier (1) operates under a given bias voltage and reference voltage, converts an input current signal into a voltage signal and amplifies it to achieve transimpedance amplification. The rear-stage amplifier circuit (2) uses the same reference voltage as the front-stage transimpedance amplifier (1) to further amplify the voltage signal output by the front-stage transimpedance amplifier (1). EA1 (31) and D1 (33) in the output signal detection circuit (3) form a valley detection circuit, which can obtain the minimum value of the output voltage signal on the capacitor (36). EA2 (32) and D2 (34) form a peak detection circuit, which can obtain the maximum value of the output voltage signal at the anode of D3 (35). When powered on, EA2 (32) outputs a high voltage, and charges the capacitor (36) through D2 (34) and D3 (35). When this voltage is greater than the output voltage, EA1 (31) outputs a low voltage, which starts the valley detection circuit and discharges the capacitor (36). The minimum value of the output voltage signal can be obtained and used as the offset elimination control voltage (V DCOC ) is connected to the negative input terminal of the compensation input in the preceding transimpedance amplifier (1). When the circuit is offset and causes the output static voltage to change, compensation is performed through negative feedback to reduce the output offset voltage, and finally an output voltage signal with the offset voltage reduced is obtained.

2. The single-ended output transimpedance amplifier circuit with low offset voltage according to claim 1; wherein: The front-stage transimpedance amplifier (1) in the circuit may be one of various transimpedance amplifiers such as a feedback structure transimpedance amplifier (TIA) with a compensation input, a common-gate structure TIA, a regulated common-gate structure TIA, or a TIA with a current amplifier. The input current of the front-stage transimpedance amplifier (1) in the circuit may be one of various current signals such as a current signal output by a photoelectric sensor such as a photodiode or a phototransistor, a bioelectric signal, etc.

3. The single-ended output transimpedance amplifier circuit with low offset voltage according to claim 1; wherein: The post-stage amplifier circuit (2) is an amplifier circuit that outputs an in-phase proportional amplified voltage, and can be composed of discrete devices or integrated circuits. Its manufacturing process can be any one of integrated circuit processes such as bipolar transistor process (BJT), standard complementary metal oxide semiconductor process (CMOS), bipolar complementary metal oxide semiconductor process (BiCMOS), gallium arsenide semiconductor process (GaAs), silicon germanium semiconductor process (SiGe) and silicon-on-insulator complementary metal oxide semiconductor process (SOI CMOS). The post-stage amplifier circuit (2) can be obtained by any method such as cascading an odd number of in-phase proportional amplifier circuits or cascading an even number of reverse proportional amplifier circuits.

4. The single-ended output transimpedance amplifier circuit with low offset voltage according to claim 1; Its characteristics are: The output signal detection circuit (3) can be composed of discrete devices or integrated circuits. The diodes (33), (34), (35) can be PN junctions, bipolar transistors with base and collector short-circuited, or field effect transistors with gate and drain short-circuited, any of which can achieve unidirectional conduction characteristics.

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