A transimpedance amplifier

Abstract

The present invention discloses a transimpedance amplifier, comprising: an amplifier and a voltage-controlled resistor connected to the amplifier; a gain control circuit, connected to the voltage-controlled resistor, for controlling the voltage across the voltage-controlled resistor to gradually decrease as time elapses, and the amplification gain of the amplifier to gradually increase as time elapses. The device in the present invention can produce low-gain and large-range characteristics in the detection of strong echo photocurrent signals of close targets (short echo time), while having high-gain and small-range characteristics in the detection of weak echo photocurrent signals of distant targets (long echo time). It can solve the problem that the existing logarithmic amplifier has large noise under weak signal echoes, resulting in insufficient signal-to-noise ratio of the system, and meets the index requirements of large dynamic range and low noise in lidar receivers.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic communication technologies, and in particular, to a transimpedance amplifier. Background Art

[0002] In the laser ranging system, the pulse laser time-of-flight (TOF) ranging method measures the round-trip time interval of the pulse laser between the target and the lidar receiver system, and then calculates the distance between the target and the lidar receiver system. On the other hand, the receiver analog front-end circuit mainly includes a preamplifier transimpedance amplifier and an output driver circuit, etc. Among them, the preamplifier transimpedance amplifier amplifies the photocurrent of the photodetector and converts it into a voltage. The main circuit indexes include gain, bandwidth, noise, dynamic range, etc. As a key circuit module of the analog front-end, it determines the detection ability, ranging accuracy and other performance indexes of the ranging system.

[0003] Since the laser echo energy is inversely proportional to the square of the distance, the near-range echo power is strong while the far-range echo power is weak, resulting in a large signal dynamic range. For applications with a ranging range above 100 meters, the echo dynamic range usually reaches 10,000 times. For the analog front-end circuit with an ultra-large dynamic range, the existing technical solutions are mainly analog logarithmic amplifiers, which are generally implemented by amplifiers using diode devices as feedback units. Its transimpedance gain follows a logarithmic curve with the input. It has a large gain when the input signal is weak and a small gain when the input signal is strong, which can ensure that the signal is not saturated and distorted within a large dynamic range. However, the logarithmic amplifier has the problem that the noise is large under weak signal echoes, resulting in insufficient signal-to-noise ratio of the system, which affects the ranging accuracy and operating distance of the laser TOF ranging system. Summary of the Invention

[0004] The present invention provides a transimpedance amplifier to solve the problem that the existing logarithmic amplifier has a large noise under weak signal echoes, resulting in insufficient signal-to-noise ratio of the system.

[0005] To this end, the present invention provides a transimpedance amplifier, including: an amplifier and a voltage-controlled resistor connected to the amplifier; a gain control circuit connected to the voltage-controlled resistor, configured to control the voltage across the voltage-controlled resistor to gradually decrease over time, and the amplification gain of the amplifier to gradually increase over time.

[0006] Further, the gain control circuit includes: a switching transistor M7, a resistor R7, and a capacitor C7. Both the resistor R7 and the capacitor C7 are connected to the drain of the switching transistor M7; the discharge level of the capacitor C7 is the control level of the voltage-controlled resistor.

[0007] Further, the voltage-controlled resistor is disposed between the differential input terminals of the amplifier.

[0008] Further, a voltage-controlled resistor is connected across the input terminal and the output terminal of the amplifier.

[0009] Further, the amplifier is a cascode amplifier, and the amplifier includes a first CMOS transistor M1, a second CMOS transistor M2, a third CMOS transistor M3, a fourth CMOS transistor M4, a fifth CMOS transistor M5, and a sixth CMOS transistor M6; the source electrodes of the first CMOS transistor M1 and the second CMOS transistor M2 are grounded after being respectively connected to a first resistor R1 and a second resistor R2, and the source electrodes of the third CMOS transistor M3 and the fourth CMOS transistor M4 are also grounded; the drain electrode of the third CMOS transistor M3 is connected to the source electrode of the fifth CMOS transistor M5, and the drain electrode of the fourth CMOS transistor M4 is connected to the source electrode of the sixth CMOS transistor M6; the drain electrodes of the first CMOS transistor M1, the second CMOS transistor M2, the fifth CMOS transistor M5, and the sixth CMOS transistor M6 are respectively connected in series with a third resistor R3, a fourth resistor R4, a fifth resistor R5, and a sixth resistor R6 and then connected to a power supply;

[0010] One end of the voltage-controlled resistor is connected to the source electrode of the first CMOS transistor M1 and the gate electrode of the third CMOS transistor M3, and the other end is connected to the source electrode of the second CMOS transistor M2 and the gate electrode of the fourth CMOS transistor M4;

[0011] The source electrodes of the first CMOS transistor M1 and the second CMOS transistor M2 are the input terminals of the amplifier, and the drain electrodes of the first CMOS transistor M1 and the second CMOS transistor M2 are the output terminals of the amplifier.

[0012] Further, the gain control circuit includes a data logic circuit and an analog signal generator connected to each other, and the analog signal generator outputs a control level for the voltage-controlled resistor.

[0013] The technical solution provided by the present invention has the following advantages:

[0014] 1. For the transimpedance amplifier provided by the present invention, by providing a voltage-controlled resistor connected to the amplifier and providing a gain control circuit to control the voltage (i.e., resistance) of the voltage-controlled resistor, the voltage across the voltage-controlled resistor is gradually reduced as time goes by, so that the amplification gain of the amplifier gradually increases as time goes by. Therefore, when the transimpedance amplifier is applied to a laser TOF ranging system, it can have low gain and large range characteristics in detecting strong echo photocurrent signals of short-distance targets (short echo time), and high gain and small range characteristics in detecting weak echo photocurrent signals of long-distance targets (long echo time). It can solve the problem that the existing logarithmic amplifier has large noise under weak signal echoes, resulting in insufficient signal-to-noise ratio of the system, and meet the index requirements of large dynamic range and low noise in lidar receivers.

[0015] 2. The transimpedance amplifier provided by the present invention is based on the existing common-gate structure transimpedance amplifier composed of the first CMOS transistor M1, the first resistor R1, and the third resistor R3, as well as the second CMOS transistor M2, the second resistor R2, and the fourth resistor R4. A cascode amplifier composed of the third CMOS transistor M3, the fifth CMOS transistor M5, and the fifth resistor R5, as well as the fourth CMOS transistor M4, the sixth CMOS transistor M6, and the sixth resistor R6 is introduced to form a pseudo-differential adjustment type cascode transimpedance amplifier structure, which can reduce the input impedance of the transimpedance amplifier with the common-gate structure to 1 / g m，M3 R5, improving the performance of the transimpedance amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 It is a schematic circuit diagram of a transimpedance amplifier provided by an embodiment of the present invention;

[0018] Figure 2 It is another schematic circuit diagram of a transimpedance amplifier provided by an embodiment of the present invention;

[0019] Figure 3 It is another schematic circuit diagram of a transimpedance amplifier provided by an embodiment of the present invention;

[0020] Figure 4 It is a schematic circuit diagram of a gain control circuit provided by an embodiment of the present invention;

[0021] Figure 5 For Figure 4 the schematic diagram of the control level VT of the gain control circuit in

[0022] Figure 6 For Figure 4 the schematic diagram of the amplification gain of the corresponding transimpedance amplifier of the gain control circuit in

[0023] Figure 7 It is a schematic circuit diagram of another gain control circuit provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] In the description of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0026] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0027] This embodiment provides a transimpedance amplifier, as Figure 1 shown, the transimpedance amplifier includes: an amplifier, a voltage-controlled resistor, and a gain control circuit.

[0028] In this embodiment, as Figure 1 shown, when in a transimpedance amplifier laser TOF ranging system, the input end of the transimpedance amplifier is connected to a photodiode, which is used to amplify the photocurrent in the photodiode, and as Figure 1 shown, the output end of the transimpedance amplifier can also be connected to an output buffer.

[0029] In this embodiment, the voltage-controlled resistor is connected to the amplifier, and the gain control circuit is connected to the voltage-controlled resistor, and is used to control the voltage across the voltage-controlled resistor to gradually decrease over time, and the amplification gain of the amplifier to gradually increase over time.

[0030] In this embodiment, the voltage-controlled resistor is connected to the amplifier. Specifically, the amplifier in this embodiment can be Figure 1 the differential current buffer type transimpedance amplifier shown in Figure 1The resistor R) is set between the differential input terminals of the amplifier. At this time, the transimpedance amplifier has a low input impedance to obtain a high circuit bandwidth under the condition of a large input load capacitance. After buffering, the output terminal has a high impedance, and a voltage signal can be obtained on the resistor to achieve the transimpedance amplification function. The output buffer drives and outputs the amplified voltage signal, enabling the circuit to have the ability to drive a load. Specifically, the gain control circuit controls the resistance value of the voltage-controlled resistor by controlling the level VT, thereby controlling the shunt of the input terminal, and further achieving controllable gain.

[0031] Specifically, the amplifier in this embodiment can also be Figure 2 the resistor-feedback amplifier type transimpedance amplifier shown in Figure 2 At this time, the voltage-controlled resistor (

[0032] Specifically, the amplifier in this embodiment can also be Figure 3 the transimpedance amplifier with the pseudo-differential regulation type cascode current buffer circuit structure shown in

[0033] Among them, the source electrodes of the first CMOS transistor M1 and the second CMOS transistor M2 are grounded after being respectively connected to the first resistor R1 and the second resistor R2, and the source electrodes of the third CMOS transistor M3 and the fourth CMOS transistor M4 are also grounded; the drain electrode of the third CMOS transistor M3 is connected to the source electrode of the fifth CMOS transistor M5, and the drain electrode of the fourth CMOS transistor M4 is connected to the source electrode of the sixth CMOS transistor M6; the drain electrodes of the first CMOS transistor M1, the second CMOS transistor M2, the fifth CMOS transistor M5, and the sixth CMOS transistor M6 are respectively connected in series with the third resistor R3, the fourth resistor R4, the fifth resistor R5, and the sixth resistor R6 and then connected to the power supply.

[0034] At this time, the voltage-controlled resistor ( Figure 3One end of R7) is connected to the source of the first CMOS transistor M1 and the gate of the third CMOS transistor M3, and the other end is connected to the source of the second CMOS transistor M2 and the gate of the fourth CMOS transistor M4. The sources of the first CMOS transistor M1 and the second CMOS transistor M2 are the input terminals of the amplifier, and the drains of the first CMOS transistor M1 and the second CMOS transistor M2 are the output terminals of the amplifier. At this time, M1 and M2 are current buffer MOS transistors, and R1 and R2 provide the required bias current for M1 and M2. The output current takes voltages VON and VOP at resistors R3 and R4 for output. R7, as a voltage-controlled resistor, is controlled by the gain control level VT. When the VT voltage changes, the impedance of R7 is controlled to change, thereby controlling the input shunt and achieving controllable gain of the transimpedance amplifier. When the VT voltage changes from high to low, the resistance value of R7 changes from low to high. The shunt of R7 to the input decreases, thereby controlling the overall gain to change from low to high. According to different application scenarios, this structure can be selected in differential form or single-ended form, and only a control switch needs to be added.

[0035] In this embodiment, on the basis of the existing cascode structure transimpedance amplifier composed of the first CMOS transistor M1, the first resistor R1, and the third resistor R3, and the second CMOS transistor M2, the second resistor R2, and the fourth resistor R4, a cascode amplifier composed of the third CMOS transistor M3, the fifth CMOS transistor M5, and the fifth resistor R5, and the fourth CMOS transistor M4, the sixth CMOS transistor M6, and the sixth resistor R6 is introduced to form a pseudo-differential adjustment type cascode transimpedance amplifier structure, which can reduce the input impedance of the cascode structure transimpedance amplifier to 1 / g of the original m，M3 R5, which can improve the performance of this transimpedance amplifier.

[0036] In addition, the amplifier in this embodiment can also be of other types, such as a cascode current buffer structure, a regulated cascode current buffer structure, or a voltage shunt feedback structure, etc. And according to the application scenario, the ports of the transimpedance amplifier can be in differential form, single-ended form, or other implementation manners.

[0037] In this embodiment, the gain control circuit can also adopt various types. For example, it can be an RC discharge control circuit or an analog signal generator control circuit.

[0038] In the transimpedance amplifier of this embodiment, by setting a voltage-controlled resistor connected to the amplifier and providing a gain control circuit to control the voltage (i.e., resistance) of the voltage-controlled resistor, the voltage across the voltage-controlled resistor is gradually decreased as time elapses, so that the amplification gain of the amplifier gradually increases as time elapses. As a result, when the transimpedance amplifier is applied to a laser TOF ranging system, it can have the characteristics of low gain and large range in detecting strong echo photocurrent signals of short-range targets (short echo time), and high gain and small range in detecting weak echo photocurrent signals of long-range targets (long echo time). It can solve the problem that the existing logarithmic amplifier has a large noise under weak signal echoes, resulting in insufficient signal-to-noise ratio of the system, and meet the index requirements of large dynamic range and low noise in lidar receivers.

[0039] As an alternative implementation, this embodiment provides an implementation of the gain control circuit, as Figure 4 shown. The gain control circuit includes: a switching transistor M7, a resistor R7, and a capacitor C7. Both the resistor R7 and the capacitor C7 are connected to the drain of the switching transistor M7; the discharge level of the capacitor C7 is the control level of the voltage-controlled resistor.

[0040] In this embodiment, as Figure 5 shown, the charging and discharging process of the capacitor C7 causes the gain control level VT to vary with time. When the gate power supply GT of the switching transistor M7 is high, VT is also at a high level; when the GT level changes from high to low, the RC circuit discharges, and the VT level gradually decreases with the discharge time; when the GT level changes from low to high, since the capacitor C7 is charged, the VT level gradually increases with the charging time. As a result, the voltage-controlled resistor in the analog front-end circuit changes following the charging and discharging time of the capacitor C, which realizes the variation of the gain of the transimpedance amplifier with time. Correspondingly, as Figure 6 shown, when VT is at a high level, the output signal swing is small. When VT gradually decreases with time, the differential output signal swing gradually becomes larger, realizing the selection of a low-gain mode for short echo time and strong echo signals during short-range measurements; and a high-gain mode for long echo time and weak echo signals during long-range measurements, ultimately achieving the effect of controllable gain with time.

[0041] As an alternative implementation, this embodiment also provides another implementation of the gain control circuit, as Figure 7 shown. The gain control circuit includes an interconnected data logic circuit and an analog signal generator, and the analog signal generator outputs the control level of the voltage-controlled resistor.

[0042] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or alterations can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or alterations derived therefrom still fall within the protection scope of the present invention.

Claims

1. A transimpedance amplifier, characterized in that, Comprising: An amplifier and a voltage-controlled resistor connected to the amplifier; the amplifier is a cascode amplifier, and the amplifier includes a first CMOS transistor M1, a second CMOS transistor M2, a third CMOS transistor M3, a fourth CMOS transistor M4, a fifth CMOS transistor M5, and a sixth CMOS transistor M6; the source electrodes of the first CMOS transistor M1 and the second CMOS transistor M2 are respectively connected to a first resistor R1 and a second resistor R2 and then grounded, and the source electrodes of the third CMOS transistor M3 and the fourth CMOS transistor M4 are also grounded; the drain electrode of the third CMOS transistor M3 is connected to the source electrode of the fifth CMOS transistor M5, and the drain electrode of the fourth CMOS transistor M4 is connected to the source electrode of the sixth CMOS transistor M6; the drain electrodes of the first CMOS transistor M1, the second CMOS transistor M2, the fifth CMOS transistor M5, and the sixth CMOS transistor M6 are respectively connected in series with a third resistor R3, a fourth resistor R4, a fifth resistor R5, and a sixth resistor R6 and then connected to the power supply; One end of the voltage-controlled resistor is connected to the source electrode of the first CMOS transistor M1 and the gate electrode of the third CMOS transistor M3, and the other end is connected to the source electrode of the second CMOS transistor M2 and the gate electrode of the fourth CMOS transistor M4; The source electrodes of the first CMOS transistor M1 and the second CMOS transistor M2 are the input terminals of the amplifier, and the drain electrodes of the first CMOS transistor M1 and the second CMOS transistor M2 are the output terminals of the amplifier; A gain control circuit, connected to the voltage-controlled resistor, for controlling the voltage across the voltage-controlled resistor to gradually decrease as time elapses, and the amplification gain of the amplifier to gradually increase as time elapses.

2. The transimpedance amplifier according to claim 1, wherein The gain control circuit includes: a switching transistor M7, a resistor R7, and a capacitor C7, and both the resistor R7 and the capacitor C7 are connected to the drain electrode of the switching transistor M7; the discharge level of the capacitor C7 is the control level of the voltage-controlled resistor.

3. The transimpedance amplifier according to claim 1 or 2, wherein The voltage-controlled resistor is disposed between the differential input terminals of the amplifier.

4. The transimpedance amplifier according to claim 1 or 2, characterized in that, The voltage-controlled resistor is connected across the input terminal and the output terminal of the amplifier.

5. The transimpedance amplifier according to claim 1, wherein The gain control circuit includes a data logic circuit and an analog signal generator connected to each other, and the analog signal generator outputs the control level of the voltage-controlled resistor.

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