DC current cancellation scheme for an optical receiver

Patent metadata

Field	Value
Publication number	US-10944486-B2
Application number	US-201715833314-A
Country	US
Kind code	B2
Filing date	Dec 6, 2017
Priority date	Dec 6, 2017
Publication date	Mar 9, 2021
Grant date	Mar 9, 2021

Abstract

In high data rate receivers, comprising a photodetector (PD) and a transimpedance amplifier (TIA), a transmitted optical signal typically has poor extinction ratio, which translates into a small modulated current with a large DC current at the output of the PD. The large DC current saturates the TIA, which significantly degrades the gain and bandwidth performance. Accordingly, cancelling photo diode DC current in high data rate receivers is important for proper receiver operation. A DC current cancellation loop, comprising a low pass filter section and a trans-conductance cell (GM) are connected to the input of the TIA. PD DC current I DC is drawn from the input node of the TIA in the GM cell, such that the cancellation loop maintains the DC voltage value of the TIA input node to be the same as a reference voltage (V REF ).

First claim

We claim:

1. An optical receiver comprising:
a first photodetector (PD) for converting a first input optical signal into a first PD current comprising a first AC component and a first DC component;
a first transimpendance amplifier (TIA) for converting the first AC component into a first voltage signal, the first TIA comprising a first TIA input;
a signal path electrically connecting the first TIA to the first PD; and
a first DC cancellation loop connected to the signal path between the first PD and the first TIA for cancelling the first DC component, the first DC cancellation loop comprising:
a first input and a first output each connected to the first TIA input;
a first trans-conductance cell capable of drawing in the first DC component, such that the first DC cancellation loop maintains a DC voltage at the first TIA input substantially the same as a reference voltage, wherein the reference voltage is equal to an input voltage to the first TIA for a zero DC current condition;
a first low pass filter; and
a replica TIA configured to provide the reference voltage to the first trans-conductance cell, wherein the replica TIA is a replica of the first TIA.

2. The optical receiver according to claim 1 , wherein the first low pass filter comprises a first resistor and a first capacitor; and wherein the first capacitor is placed away from the signal path between the first TIA and the first PD.

3. The optical receiver according to claim 1 , wherein the first DC cancellation loop is configured to have an upper speed limit, which is equal or smaller than a lowest frequency component of the first input optical signal, and a lower speed limit, which is equal or greater than a fastest variation of the first DC component.

4. The optical receiver according to claim 1 , wherein the replica TIA comprises a floating input.

5. An optical receiver comprising:
a first photodetector (PD) for converting a first input optical signal into a first PD current comprising a first AC component and a first DC component;
a first transimpendance amplifier (TIA) for converting the first AC component into a first voltage signal, the first TIA comprising a first input;
a signal path electrically connecting the first TIA to the first PD; and
a first DC cancellation loop connected to the signal path between the first PD and the first TIA for cancelling the first DC component, the first DC cancellation loop comprising:
a first input and a first output each connected to the first input of the first TIA;
a first trans-conductance cell capable of drawing in the first DC component, such that the first DC cancellation loop maintains a first DC voltage value of the first input of the first TIA substantially the same as a first reference voltage, wherein the first reference voltage is equal to an input voltage to the first TIA for a zero DC current condition; and
a first low pass filter;
wherein the first trans-conductance cell comprises a voltage amplifier, a bias current source, a differential pair (T 1 , T 2 ) of transistors, and a current mirror;

wherein an AC trans-conductance GM of the first trans-conductance cell is generally proportional to a product of a gain A of the voltage amplifier, a trans-conductance g m of the differential pair (T 1 , T 2 ), and a scaling factor N of the current mirror, wherein N≥1.

6. The optical receiver according to claim 5 , wherein the first low pass filter comprises a miller capacitor disposed between an input and an output of the voltage amplifier.

7. The optical receiver according to claim 5 , wherein N is between 4 and 40.

8. An optical receiver comprising:
first and second photodetectors (PD) each for converting an input optical signal into a PD current comprising an AC component and a DC component;
a first differential transimpendance amplifier (TIA) comprising a first TIA input electrically connected to the first PD and a second TIA input electrically connected to the second PD;
first and second DC cancellation loops connected to the first and second TIA inputs, respectively, for cancelling the DC components, each of the first and second DC cancellation loops comprising:
an input and an output connected to one of the TIA inputs;
a trans-conductance cell capable of drawing one of the DC components to maintain a DC voltage at one of the TIA inputs substantially the same as a reference voltage; and
a low pass filter; and

at least one replica TIA configured to provide, to the trans-conductance cells, the reference voltages being equal to input voltages to the first and second TIA inputs for a zero input DC current condition.

9. The optical receiver according to claim 8 , further comprising:
an input port for inputting a combined optical signal;
a polarization beam splitter for splitting the combined optical signal into first and second polarized components;
a local oscillator for generating first and second oscillator components;
a first hybrid mixer for generating first and second phase differentiated optical signals from the first polarized component and the first oscillator component;
a second hybrid mixer for generating third and fourth phase differentiated optical signals from the second polarized component and the second oscillator component;
wherein the input optical signals comprise the first and second phase differentiated optical signals.

Assignees

• Elenion Tech Llc

Inventors

• Ahmed Mostafa
• Rylyakov Alexander

Classifications

• H04B10/60

  Receivers · CPC title

• H03F1/00

  Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements · CPC title

• H04B10/6911 Primary

  Photodiode bias control, e.g. for compensating temperature variations · CPC title

• H03F3/00

  Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements · CPC title

• H04B10/671

  for controlling the input optical signal · CPC title