US-12618712-B2 - Differential transimpedance amplifier from a single photodiode

Abstract

An integrated circuit is disclosed. The integrated circuit comprises an input interface and an optical receiver. The optical receiver includes a photodiode, level shifter, and differential transimpedance amplifier (TIA). The photodiode has a cathode and anode terminal and is configured to receive an optical signal via the input interface. The level shifter includes a parallel RC circuit. The differential TIA has first and second conversion circuits. The first conversion circuit is connected to the cathode terminal and a first output terminal of the optical receiver. The second conversion circuit is connected between the anode terminal and a second output terminal of the optical receiver. The parallel RC circuit is connected between the cathode terminal of the photodiode and the first conversion circuit. The differential TIA is configured to provide a differential voltage signal at the first and second output terminals of the optical receiver based on the optical signal.

Inventors

• Georgios Kalogerakis

Assignees

• NVIDIA CORPORATION

Dates

Publication Date

20260505

Application Date

20231011

Claims (20)

1. 1 . An optical receiver, comprising: a photodiode having a cathode terminal and an anode terminal; a level shifter including a parallel RC circuit; and a differential transimpedance amplifier having: a first conversion circuit connected to the level shifter and a first output terminal of the optical receiver, wherein the parallel RC circuit is connected between the cathode terminal and the first conversion circuit; and a second conversion circuit connected between the anode terminal and a second output terminal of the optical receiver, wherein the first and the second conversion circuits are different circuits and the first and the second output terminals are separate terminals, wherein the level shifter further includes a sensing loop having a sensing operational transconductance amplifier (OTA) and an output transistor, wherein either a first input terminal pair of the sensing OTA is connected to negative terminals of the first and the second conversion circuit, a second input terminal pair of the sensing OTA is connected to positive terminals of the first and the second conversion circuit, or both and an output of the OTA is connected to a gate of the output transistor.
2. 2 . The optical receiver as recited in claim 1 , further comprising a cathode biasing circuit connected between the cathode terminal and a high operating voltage of the optical receiver.
3. 3 . The optical receiver as recited in claim 2 , wherein the cathode biasing circuit includes at least one resistor connected between the cathode terminal and the anode terminal.
4. 4 . The optical receiver as recited in claim 3 , wherein the cathode biasing circuit further includes a common-mode loop connected to the at least one resistor, wherein the common-mode loop includes a common-mode operational transconductance amplifier (OTA) and a transistor, wherein an output terminal of the common-mode OTA is connected to a gate of the transistor, which provides DC current for the photodiode.
5. 5 . The optical receiver as recited in claim 4 , wherein the cathode biasing circuit includes two resistors connected in series between the cathode terminal and the anode terminal, and an input terminal of the common-mode OTA is connected to a node between the two resistors.
6. 6 . An optical-electrical apparatus, comprising: a photodiode having an anode terminal and a cathode terminal; a cathode biasing circuit connected to the cathode terminal; and a differential transimpedance amplifier configured to receive, at a first input terminal, a current from the cathode terminal and convert the received current to a first output voltage, wherein the cathode biasing circuit is configured to bias the cathode terminal at a high operating voltage of the optical-electrical apparatus and provide an impedance greater than a combined impedance of an impedance at the first input terminal and at a level shifter connected between the cathode terminal and the first input terminal, wherein the level shifter: is configured to shift a cathode terminal voltage at the cathode terminal to a lower input voltage at the first input terminal; and includes a parallel RC circuit and a current dump circuit configured to control a current through a resistor of the parallel RC circuit to shift the cathode terminal voltage to the lower input voltage at the first input terminal.
7. 7 . The optical-electrical apparatus as recited in claim 6 , wherein the differential transimpedance amplifier is further configured to receive, at a second input terminal, a current from the anode terminal and convert the received current to a second output voltage.
8. 8 . The optical-electrical apparatus as recited in claim 6 , wherein the current dump circuit is configured to control the current through the resistor of the parallel RC circuit based on DC voltages at the first input terminal and a second input terminal of the differential transimpedance amplifier.
9. 9 . The optical-electrical apparatus as recited in claim 6 , wherein the cathode biasing circuit includes at least two resistors connected in series between the cathode terminal and the anode terminal that are used to sense an input common mode voltage at the cathode and anode photodiode terminals.
10. 10 . The optical-electrical apparatus as recited in claim 9 , wherein the at least two resistors feed a common-mode loop that determines a common-mode voltage between the cathode and anode terminals of the photodiode and the cathode biasing circuit sets the cathode terminal voltage to be twice a common-mode voltage reference minus an anode terminal bias voltage.
11. 11 . The optical-electrical apparatus as recited in claim 10 , wherein the cathode biasing circuit further includes a current source connected to the cathode terminal which provides a needed DC current for the photodiode plus a DC current for the level shifter.
12. 12 . A method of manufacturing an optical receiver as recited in claim 6 .
13. 13 . An integrated circuit, comprising: input interface; and an optical receiver including: a photodiode, having a cathode terminal and an anode terminal, configured to receive an optical signal via the input interface; a level shifter including a parallel RC circuit; and a differential transimpedance amplifier having a first conversion circuit connected to the cathode terminal and a first output terminal of the optical receiver and a second conversion circuit connected between the anode terminal and a second output terminal of the optical receiver, wherein the parallel RC circuit is connected between the cathode terminal and the first conversion circuit and the differential transimpedance amplifier is configured to provide a differential voltage signal at the first and second output terminal based on the optical signal, wherein the level shifter further includes a sensing loop having a sensing operational transconductance amplifier (OTA) and an output transistor, wherein either a first input terminal pair of the sensing OTA is connected to negative terminals of the first and the second conversion circuit, a second input terminal pair of the sensing OTA is connected to positive terminals of the first and the second conversion circuit, or both and an output of the OTA is connected to a gate of the output transistor.
14. 14 . The integrated circuit as recited in claim 13 , further comprising functional circuitry connected to the first and second output terminals that generate an output based on the differential voltage signal.
15. 15 . The integrated circuit as recited in claim 13 , further comprising a cathode biasing circuit connected between the cathode terminal and a high operating voltage of the optical receiver.
16. 16 . The optical receiver as recited in claim 15 , wherein the cathode biasing circuit includes at least one resistor connected between the cathode terminal and the anode terminal.
17. 17 . The optical receiver as recited in claim 16 , wherein the cathode biasing circuit further includes a common-mode loop connected to the at least one resistor, wherein the common-mode loop includes a common-mode operational transconductance amplifier (OTA) and a transistor, wherein an output terminal of the common-mode OTA is connected to a gate of the transistor, which provides DC current for the photodiode.
18. 18 . The optical receiver as recited in claim 17 , wherein the cathode biasing circuit includes two resistors connected in series between the cathode terminal and the anode terminal, and an input terminal of the common-mode OTA is connected to a node between the two resistors.
19. 19 . A library of circuit designs, comprising: an optical receiver, the optical receiver comprising: a photodiode having a cathode terminal and an anode terminal; a level shifter including a parallel RC circuit; and a differential transimpedance amplifier having: a first conversion circuit connected to the level shifter and a first output terminal of the optical receiver, wherein the parallel RC circuit is connected between the cathode terminal and the first conversion circuit; and a second conversion circuit connected between the anode terminal and a second output terminal of the optical receiver, wherein the first and the second conversion circuits are different circuits and the first and the second output terminals are separate terminals, wherein the level shifter of the optical receiver further includes a sensing loop having a sensing operational transconductance amplifier (OTA) and an output transistor, wherein either a first input terminal pair of the sensing OTA is connected to negative terminals of the first and the second conversion circuit, a second input terminal pair of the sensing OTA is connected to positive terminals of the first and the second conversion circuit, or both and an output of the OTA is connected to a gate of the output transistor.
20. 20 . The library of circuit designs as recited in claim 19 , wherein the optical receiver further comprises a cathode biasing circuit connected between the cathode terminal and a high operating voltage of the optical receiver.

Description

TECHNICAL FIELD This application is directed, in general, to optical receivers and, more specifically, to increasing an optical signal received at optical receivers. BACKGROUND Optical to electrical communications is typically handled by implementing one or more types of photodiodes when implemented as an interface to an integrated circuit, or as part of an integrated circuit. Transimpedance amplifiers (TIAs) are used in optical receivers to convert photodiode current from received optical signals into a voltage. TIAs are inherently single ended circuits requiring a single-ended to differential conversion to be implemented at a later stage. SUMMARY OF THE DISCLOSURE In one aspect, an optical receiver is disclosed. In one embodiment, the optical receiver comprises a photodiode, a level shifter, and a differential transimpedance amplifier (TIA). In one embodiment, the photodiode has a cathode terminal and an anode terminal. In one embodiment, the level shifter includes a parallel RC circuit. In one embodiment, the differential TIA has a first conversion circuit connected to the level shifter and a first output terminal of the optical receiver. In one embodiment, the parallel RC circuit of the level shifter is connected between the cathode terminal of the photodiode and the first conversion circuit. In another aspect, an optical-electrical apparatus is disclosed. In one embodiment, the optical-electrical apparatus comprises a photodiode, a cathode biasing circuit, and a differential transimpedance amplifier (TIA). In one embodiment, the photodiode has an anode terminal and a cathode terminal. In one embodiment, the cathode biasing circuit is connected to the cathode terminal of the photodiode. In one embodiment, the differential TIA is configured to receive, at a first input terminal, a current from the cathode terminal of the photodiode and is configured to convert the received current to a first output voltage. In one embodiment, the cathode biasing circuit is configured to bias the cathode terminal of the photodiode at a high operating voltage and configured to provide an impedance greater than a combined impedance of an impedance at the first input terminal and a level shifter connected between the cathode terminal of the photodiode and the first input terminal. In another aspect, an integrated circuit is disclosed. In one embodiment, the integrated circuit comprises an input interface and an optical receiver. In one embodiment, the optical receiver includes a photodiode, a level shifter, and a differential transimpedance amplifier (TIA). In one embodiment, the photodiode has a cathode terminal and an anode terminal and is configured to receive an optical signal via the input interface. In one embodiment, the level shifter includes a parallel RC circuit. In one embodiment, the differential TIA has a first conversion circuit and a second conversion circuit. In one embodiment, the first conversion circuit is connected to the cathode terminal of the photodiode and a first output terminal of the optical receiver. In one embodiment, the second conversion circuit is connected between the anode terminal of the photodiode and a second output terminal of the optical receiver. In one embodiment, the parallel RC circuit is connected between the cathode terminal of the photodiode and the first conversion circuit. In one embodiment, the differential TIA is configured to provide a differential voltage signal at the first and second output terminals of the optical receiver based on the optical signal. In another aspect, a library of circuit designs is disclosed. In one embodiment, the library of circuit designs comprises an optical receiver, the optical receiver comprising a photodiode, a level shifter, and a differential transimpedance amplifier. In one embodiment, the photodiode has a cathode terminal and an anode terminal. In one embodiment, the level shifter includes a parallel RC circuit. In one embodiment, the differential TIA has a first conversion circuit connected to the level shifter and a first output terminal of the optical receiver. In one embodiment, the parallel RC circuit is connected between the cathode terminal of the photodiode and the first conversion circuit. BRIEF DESCRIPTION OF THE DRAWINGS Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: FIG. 1 illustrates a block diagram of an integrated circuit having an example of an optical receiver constructed according to the principles of the disclosure; FIG. 2 illustrates a circuit diagram of an example of an integrated circuit having an optical receiver constructed according to principles of the disclosure; FIG. 3 illustrates a block diagram of an example of an optical receiver constructed according to the principles of the disclosure; FIG. 4. illustrates a schematic diagram of an example of an optical receiver constructed according to the principles of the disclosure; and FIG. 5 illustrate