Amplifier input protection circuits
Amplifier input protection circuits are described. In one embodiment, a photoreceiver for a lidar system has a photodetector configured to generate an output current in response to received light. A transimpedance amplifier is configured to receive the output current and generate a voltage output corresponding to the output current in response thereto, and a diode circuit has a cathode coupled at a node between the photodetector output and the transimpedance amplifier input.
1. A transimpedance amplifier protection circuit comprising:
a photoreceiver for a lidar system having a photodetector configured to generate an output current in response to received light;
a transimpedance amplifier configured to receive the output current and generate an output voltage corresponding to the output current in response thereto;
a protection diode circuit having a cathode coupled at an input node between the photodetector output and the transimpedance amplifier input; and
a clamping diode coupled between the input node and an intermediate node of the transimpedance amplifier, the clamping diode configured to prevent overvoltage between the input node and the intermediate node.
2. The circuit of claim 1 , wherein the protection diode circuit has a grounded anode.
3. The circuit of claim 1 , wherein the protection diode circuit is configured to reduce the capacitance at the transimpedance amplifier input.
4. The circuit of claim 1 , wherein the protection diode circuit has a barrier voltage above which the protection diode circuit provides a current path to ground, wherein the barrier voltage is below the damage threshold of the transimpedance amplifier.
5. The circuit of claim 1 , wherein the protection diode circuit comprises a first and a second parallel diode, each with grounded anodes and each with cathodes coupled to the input node and a resistor between the two cathodes.
6. The circuit of claim 5 , wherein the resistor is an active resistor.
7. The circuit of claim 5 , wherein the first diode cathode is between the photodetector and the resistor and wherein the second diode has a higher barrier voltage than the first diode.
8. The circuit of claim 5 , wherein the first diode cathode is between the photodetector and the resistor and wherein the first diode and second diode have equivalent barrier voltages.
9. The circuit of claim 5 , wherein the resistor is configured as a current limiting resistor to reduce high currents from the photodetector to the transimpedance amplifier.
10. An active camera system, comprising:
a light source configured to emit light as a series of one or more light pulses;
a scanner configured to direct the one or more light pulses towards a remote target at a particular position in a two-dimensional field of regard; and
a receiver configured to detect one or more light pulses scattered by the remote target, the receiver including:
a photoreceiver having a photodetector configured to generate an output current in response to received light;
a transimpedance amplifier configured to receive the output current and generate an output voltage corresponding to the output current in response thereto; and
a protection diode circuit having a cathode coupled at an input node between the photodetector output and the transimpedance amplifier input; and
a clamping diode coupled between the input node and an intermediate node of the transimpedance amplifier, the clamping diode configured to prevent overvoltage between the input node and the intermediate node.
11. A method of imaging a remote target, comprising:
generating a light pulse for a position in a two-dimensional scanning field of regard;
emitting the generated light pulse toward a remote target in the position of the two-dimensional field of regard;
receiving a scattered light pulse scattered from the remote target at a photodetector and generating a current output;
generating an output voltage corresponding to the current output at a transimpedance amplifier configured to receive the photodetector output;
sinking current from the photodetector to ground when the current output exceeds a barrier voltage of a protection diode circuit having:
a grounded anode and a cathode coupled at an input node between the photodetector output and the transimpedance amplifier input; and
a clamping diode coupled between the input node and an intermediate node of the transimpedance amplifier, the clamping diode configured to prevent overvoltage between the input node and the intermediate node;
detecting a receive time associated with the received scattered light pulse;
determining a range to the target based on the receive time of the received scattered light pulse;
detecting an intensity of the received scattered light pulse; and
determining a reflectivity of the remote target from the determined range to the remote target and the detected intensity of the received scattered light pulse.
12. The circuit of claim 1 , wherein the transimpedance amplifier comprises a common source stage and a common gate stage and wherein the intermediate node is between the common source stage and the common gate stage.
13. The circuit of claim 12 , wherein the clamping diode is configured to prevent the overvoltage between a gate and a drain of the common source stage.
14. The circuit of claim 12 , wherein the clamping diode is configured to prevent the overvoltage between a gate and a source of the common source stage.
15. The circuit of claim 1 , wherein the clamping diode comprises a diode connected field effect transistor.
16. The circuit of claim 1 , wherein the clamping diode has an anode coupled to the input node and a cathode coupled to the intermediate node.
17. The circuit of claim 16 , wherein the clamping diode further comprises a second parallel diode having an anode coupled to the intermediate node and a cathode coupled to the input node.
18. The circuit of claim 1 , further comprising:
a current source coupled to a voltage output node of the transimpedance amplifier, wherein the output voltage of the transimpedance amplifier is supplied to the voltage output node; and
a current pinch off circuit between the current source and the output node configured to pinch off a current of the current source when the output voltage exceeds a second overvoltage.
19. The circuit of claim 18 , wherein the current pinch off circuit is a field effect transistor, having a regulated input bias voltage.
20. The circuit of claim 19 , wherein the regulated input bias voltage is regulated based, at least in part, on threshold voltages of the transimpedance amplifier.
21. The circuit of claim 18 , wherein the transimpedance amplifier comprises a cascode chain and wherein the current pinch-off circuit is coupled between the current source and the cascode chain.