Automatic gain control loop

• US 10,171,057 B1
• Filed: 03/21/2018
• Issued: 01/01/2019
• Est. Priority Date: 03/21/2018
• Status: Active Grant

• Current Assignee: Nokia Solutions and Networks US LLC (Nokia Corporation)
• Original Assignee: Elenion Technologies, LLC (Nokia Corporation)
• Inventors: Ahmed, Mostafa, Rylyakov, Alexander
• Primary Examiner(s): Payne, David
• Assistant Examiner(s): Ismail, Omar S
• Application Number:
  US15/927,537
• Time in Patent Office: 286 Days
• CPC Class Codes: H03F 2200/129 there being a feedback over the complete amplifier
• CPC Class Codes: H03F 3/08 controlled by light
• CPC Class Codes: H03F 3/16 with field-effect devices
• CPC Class Codes: H03F 3/68 Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics power amplifiers using a combination of several semiconductor amplifiers H03F3/211; combinations of amplifiers using coupling networks with distributed constants H03F3/602
• CPC Class Codes: H03G 1/0035 using continuously variable impedance elements
• CPC Class Codes: H03G 2201/103 being an amplifying element
• CPC Class Codes: H03G 3/3084 in receivers or transmitters for electromagnetic waves other than radiowaves, e.g. lightwaves H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H04B 10/6931 Automatic gain control of the preamplifier

Abstract

In conventional optical receivers the dynamic range is obtained by using variable gain amplifiers (VGA) with a fixed trans-impedance amplifier (TIA) gain. To overcome the SNR problems inherent in conventional receivers an improved optical receiver comprises an automatic gain control loop for generating at least one gain control signal for controlling gain of both the VGA and the TIA. Ideally, both the resistance and the gain of the TIA are controlled by a gain control signal.

Claims

1. An optical receiver comprising:

a photodetector for converting an optical signal into an input electrical current signal;

a transimpedance amplifier (TIA) for converting the input electrical current signal into an input voltage signal, the TIA including a variable feedback resistor and a variable gain feed-forward amplifier;

a variable gain amplifier (VGA) for amplifying the input voltage signal to a desired voltage level; and

an automatic gain control loop for generating a first gain control signal for controlling gain of the VGA, and a second gain control signal for controlling the gain of the TIA;

wherein the automatic gain control loop further comprises a signal conditioning circuit for generating the second gain control signal for controlling gain of the TIA based on the first gain control signal;

wherein the second gain control signal is capable of adjusting a value of the variable feedback resistor, whereby the TIA gain varies linearly with a level of the second gain control signal; and

wherein the second gain control signal is also capable of varying a feed forward gain A_o of the TIA.

2. The optical receiver according to claim 1, wherein the at least one gain control signal is based on a reference voltage, which is based on the desired voltage level.

3. The optical receiver according to claim 1, wherein the automatic gain control loop is capable of generating the first gain control signal, whereby the VGA gain varies linearly with a level of the first gain control signal.

4. The optical receiver according to claim 1, wherein the second gain control signal is capable of varying the value of the feedback resistor R_F and the feed forward gain A_o simultaneously with substantially a same ratio.

5. The optical receiver according to claim 1, further comprising an analog to digital converter (ADC) for converting the amplified input voltage signal into a digital signal.