CN101852851B - Gain-variable trans-impedance amplifier integrated circuit for pulse laser range finder echo receiver - Google Patents

Abstract

The invention discloses a gain-variable transimpedance amplifier integrated circuit for pulse laser range finder echo reception, belonging to the technical field of integrated circuit design. The integrated circuit is based on CMOS integration technology. The narrow pulse photocurrent signal generated by the photodetector is converted into a voltage signal by the current buffer and the differential transimpedance amplifier, and then the R-2R resistance attenuation network is attenuated according to the given digital control input. After attenuation, it is amplified to a certain level by the broadband voltage amplifier and buffered and output by the output buffer. The single-chip integration of multiple functional module circuits in the existing pulse laser rangefinder is realized, the integration degree of the receiving circuit is improved, and the mass production cost of the system is reduced. At the same time, it is also conducive to the realization of highly integrated multi-element laser echo detection.

Description

Gain-variable transimpedance amplifier integrated circuit for echo reception of pulsed laser range finder

technical field

The present invention relates to integrated circuit design technology, and specifically refers to a gain-variable transimpedance amplifier integrated circuit used for echo reception of a pulsed laser rangefinder, which is used for the echo narrow pulse photocurrent signal of a pulsed laser rangefinder Transform and amplify.

Background technique

Compared with other non-contact ranging methods, pulsed laser ranging has the advantages of simple structure, no need for target cooperation, long range and fast measurement speed, making it widely used in aerospace, military and industrial fields. The pulse laser range finder sends a light pulse to the target, and after being reflected by the target, it is received by the echo receiving channel of the range finder, and the distance between the pulse and the target can be obtained by measuring the time elapsed from the emission of the light pulse to the return to the laser range finder. distance. Pulse laser ranging combined with two-dimensional scanning or focal plane detection technology can also achieve laser three-dimensional imaging of targets. The echo receiving channel is generally composed of a photodetector and a transimpedance amplifier circuit. The transimpedance amplifier circuit is used to convert and amplify the weak narrow pulse current signal output by the photodetector into a voltage pulse signal of a certain amplitude. Since the signal-to-noise ratio and rise time of the output pulse signal of the transimpedance amplifier circuit directly affect the single ranging accuracy of the pulse laser rangefinder, its gain, bandwidth and noise performance have a key impact on the performance of the entire rangefinder system.

The existing gain-variable transimpedance amplifying circuits for pulse laser rangefinder echo reception usually use multiple chips to realize their functions. In this case, the requirements of high precision, high sensitivity and large dynamic range often lead to excessive power consumption and volume of the circuit, which is not conducive to the lightweight, miniaturization and mass production of the laser rangefinder system. At the same time, the external interconnection of the chip makes the circuit more susceptible to electromagnetic radiation interference.

Contents of the invention

The purpose of the present invention is to provide a single-chip gain variable transimpedance amplifier based on CMOS integrated circuit technology that can be used for pulse laser range finder echo reception, and solve the technical deficiencies in the existing design methods.

The purpose of the present invention is achieved by the following technical approach:

Using CMOS integrated circuit technology, as shown in Figure 1, the circuit module includes a current buffer input stage, a differential transimpedance amplifier, an R-2R resistance attenuation network, a broadband voltage amplifier and an output buffer, where:

1) The current buffer input stage is used as the first stage of the circuit input, and the basic circuit diagram is shown in Figure 2. The RGC circuit (Regulated Cascode Circuit) is used to achieve low input impedance and high output impedance, which effectively isolates the input capacitance of the circuit (including the parasitic capacitance of the photodetector and the parasitic capacitance of the interconnection line) and the input impedance of the differential transimpedance amplifier, reducing the large The effect of the circuit input capacitance on the circuit bandwidth.

2) The differential transimpedance amplifier is configured with a differential amplifier plus a feedback resistor to convert the input current signal into a voltage signal.

3) The circuit diagram of the R-2R resistance attenuation network is shown in Figure 3. The resistors are implemented with NMOS tubes, which can overcome the bias level changes caused by the passive resistor attenuation network when the stages are directly coupled. The bias level V _b is consistent with the output DC level of the previous stage. Adopt 3-bit binary code digital control method, convert 3-bit binary code into 8-bit thermal unique code, select the corresponding node output in the resistance attenuation network, and realize 7 steps, each step 6-dB gain change.

4) The broadband voltage amplifier is formed by cascading multiple transconductance-transimpedance voltage amplifiers. The transconductance-transimpedance amplifier, as shown in Figure 4, is composed of two stages internally. The first stage is a transconductance stage, which provides transconductance for the input voltage signal. The second stage is a transimpedance stage, and its feedback resistance is the transconductance of the first stage. The conduction current provides an equivalent load. With this circuit configuration, a larger voltage gain can be obtained by increasing the feedback resistance. At the same time, since each pole of the circuit is not directly related to the feedback resistor, broadband applications can be realized. Multiple transconductance-transimpedance voltage amplifiers are cascaded to provide sufficient post-stage voltage gain under the premise of ensuring a certain bandwidth.

5) The output buffer uses a source follower to achieve a small output impedance and provide sufficient drive capability to drive an off-chip resistive load.

The working method of the present invention is: the photodetector is capacitively coupled to the input pin of the chip, and the narrow pulse photocurrent signal generated by it is converted into a voltage signal by the current buffer input stage and the differential transimpedance amplifier, and then passed through the R-2R resistance attenuation network According to the 3-bit binary control code given by the control circuit, after the corresponding multiple attenuation is performed, it is amplified to a certain amplitude by the broadband voltage amplifier and buffered and output by the output buffer.

Compared with the prior art, the present invention has following advantages:

1) Using CMOS integration technology, a single chip realizes a transimpedance amplifier circuit with variable gain, which can reduce the power consumption and volume of the circuit, and is conducive to the light weight, miniaturization and mass production of the laser rangefinder system. At the same time, it is beneficial to the realization of highly integrated multi-element laser echo detection.

2) The electromagnetic radiation interference coupled through the external interconnection of the chip is reduced.

3) The gain of the transimpedance amplifier is digitally controlled, and its binary control code can be easily generated by the digital control circuit of the laser rangefinder, which simplifies the gain control loop of the system.

Description of drawings

Fig. 1 is a schematic diagram of the basic structure of the present invention, which consists of five parts including a current buffer input stage, a differential transimpedance amplifier, an R-2R resistance attenuation network, a broadband voltage amplifier and an output buffer.

FIG. 2 is a schematic diagram of the basic circuit of the current buffer input stage of the present invention, using an RGC circuit (Regulated Cascode Circuit).

Fig. 3 is the realization circuit diagram of the R-2R resistance attenuation network.

The circuit diagram of the transconductance-transimpedance amplifier used in the broadband voltage amplifier of Fig. 4. Among them, the NMOS tubes M ₁ , M ₂ , I _S1 and the load resistor _RD1 constitute the first stage of the circuit, that is, the transconductance stage. NMOS transistors M ₃ , M4 , I _S2 , load resistor _RD2 and feedback resistor R _f constitute the second stage of the circuit, namely the transimpedance stage.

Detailed ways

Example

Using 0.6-μm mixed-signal CMOS technology, design a gain-variable transimpedance amplifier integrated circuit with the following input and output requirements: the input pulse photocurrent amplitude range is 0.1μA-10μA, the rise time is 4ns, and the circuit input capacitance is about 5pF. The required output pulse voltage amplitude range is about 1-2V.

In order to achieve high ranging accuracy, the transimpedance amplifier circuit should keep the rising edge of the pulse signal as short as possible. According to signal theory, the minimum bandwidth required to maintain a 4ns rise time is about 110MHz. At the same time, according to the input and output signal amplitude, the maximum gain that the transimpedance amplifier needs to provide is at least 120dBΩ, and the dynamic range of gain control is at least 40dB.

The specific implementation plan is as follows:

1) The current buffer input stage adopts RGC circuit. Adjust the parameters of each MOS tube to make the input impedance about 100Ω, and the pole formed by the 5pF input capacitor is outside 300MHz, which will not affect the overall bandwidth of the circuit. The output impedance is 20kΩ, which is directly coupled with a differential transimpedance amplifier with low input impedance, which ensures a small level loss.

2) The differential transimpedance amplifier is configured with a differential amplifier plus a feedback resistor to convert the input current signal into a voltage signal. The feedback resistor adopts NMOS tube resistor, which can realize higher transimpedance gain. With a source follower output stage, the output impedance is 490Ω (single-ended), which can be directly coupled with the R-2R resistance attenuation network without too much gain loss and bandwidth loss. The current-buffered input stage is cascaded with a differential transimpedance amplifier to achieve 85dBΩ gain (differential) and 170MHz bandwidth.

3) The resistance in the R-2R resistance attenuation network is implemented by an NMOS tube, and the R is set to be about 1kΩ by adding a bias to the on-chip bias voltage. In order to reduce the parasitic effect, the switching tube adopts the smallest size NMOS tube. The input binary control word is 3 bits, which is converted into 8-bit hot unique code by the 3-8 decoder, so as to realize a total of 42dB step attenuation control. In order not to affect the overall bandwidth of the circuit, the R-2R resistance attenuation network is buffered by the buffer output to ensure the overall circuit bandwidth performance.

4) The transconductance-transimpedance amplifier in the broadband voltage amplifier realizes a 24dB (differential) voltage gain and a bandwidth of about 230MHz, and adopts 2-stage cascading to realize a total gain of 48dB and a bandwidth of 160MHz.

5) The output buffer adopts a source-follower circuit to achieve an output impedance of 100, which can directly drive an off-chip load. The entire transimpedance amplifier integrated circuit achieves a maximum gain of 131dBΩ, 7 steps, a total gain dynamic range of 42dB, and a bandwidth of 120MHz.

Claims (4)

1. A gain-variable transimpedance amplifier integrated circuit for pulse laser rangefinder echo reception, including the following functional modules: current buffer input stage, differential transimpedance amplifier, R-2R resistance attenuation network, broadband voltage amplifier and The output buffer is characterized in that: a current buffer input stage is added between the photodetector and the differential transimpedance amplifier. After the resistance attenuation network attenuates according to the attenuation multiple given by the digital control input, it is amplified to a certain amplitude by the broadband voltage amplifier and buffered and output by the output buffer. 2. A kind of gain-variable transimpedance amplifier integrated circuit for pulse laser range finder echo reception according to claim 1, it is characterized in that: described current buffering input stage adopts RGC circuit, realizes input low impedance And output high impedance, effectively isolate the input capacitance of the circuit and the input impedance of the differential transimpedance amplifier, and reduce the influence of the input capacitance of the circuit on the circuit bandwidth. 3. A kind of gain-variable transimpedance amplifier integrated circuit for pulse laser range finder echo receiving circuit according to claim 1, it is characterized in that: described R-2R resistance attenuation network is made up of NMOS tube array , realize 7 steps controlled by 3-bit binary code, each step 6-dB gain change level. 4. A kind of gain-variable transimpedance amplifier integrated circuit that is used for pulse laser range finder echo reception according to claim 1, is characterized in that: described broadband voltage amplifier is made of multistage transconductance-transimpedance amplifier Cascade configuration to achieve sufficient voltage gain and bandwidth.

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