Automatic transimpedance control amplifier having a variable impedance feedback

• US 5,602,510 A
• Filed: 06/08/1995
• Issued: 02/11/1997
• Est. Priority Date: 07/08/1993
• Status: Expired due to Term

• Current Assignee: Skyworks Solutions Incorporated
• Original Assignee: Anadigics Incorporated (Coherent Corp.)
• Inventors: Laverick, Timothy M., Bayruns, Robert J.
• Primary Examiner(s): Fahmy, Wael
• Assistant Examiner(s): Abraham, Fetsum
• Application Number:
  US08/406,279
• Time in Patent Office: 614 Days
• Field of Search: 330/86, 330/110, 330/136, 330/282, 330/311
• US Class Current: 330/282
• CPC Class Codes: H03F 3/082 with FET's H03F3/085 takes precedence
• 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

Abstract

An automatic transimpedance control amplifier is disclosed. The amplifier incorporates an automatic gain control circuit which simultaneously and automatically adjust the value of transimpedance and the voltage gain at each gain stage of the amplifier according to the input current. The amplifier has wide bandwidth, high sensitivity/and more importantly, wide dynamic range.

Claims

1. A wide dynamic range transimpedance amplifier comprising:

an amplifier including a signal input terminal for receiving input signal and a signal output terminal for providing output signal and at least one gain stage having a controllable gain;

a controllable variable impedance feedback branch coupled between said input and output terminals; and

a control circuit coupled to control the impedance of said variable impedance feedback branch and the gain of said gain stage to maintain the transimpedance amplifier within its stable operating regime,

said control circuit being operably responsive to an increase of the magnitude of said input signal to reduce the impedance of the feedback branch and the gain of the gain stage, thereby maintaining the stability of said transimpedance amplifier when the magnitude of said input signal is increased.

2. The transimpedance amplifier of claim 1 wherein said controllable variable impedance feedback branch comprises a feedback resistor coupled in parallel with a feedback FET having a gate terminal coupled to said control circuit,

said control circuit operating to control said feedback FET such that, if the magnitude of said input signal is low, said feedback FET is turned off and the feedback impedance is approximately the resistance of said feedback resistor, and

if the magnitude of said input signal increases, said feedback FET begins to turn on, thereby reducing the impedance of said feedback branch.

3. The transimpedance amplifier of claim 2 wherein said gain stage includes a gain control FET for controlling the gain of said gain stage,

said gain control FET having a drain terminal coupled to an output node of said gain stage and a gate terminal coupled to said control circuit, and the gain of said gain stage being controlled by a voltage applied to said gate terminal by said control circuit,

said control circuit operating to control the gain of the gain stage such that, if the magnitude of said input signal is low, said gain control FET is turned off and said gain stage displays a maximum gain, and

if the magnitude of said input signal increases, said gain control FET begins to turn on, thereby reducing the gain of said gain stage.

4. The transimpedance amplifier of claim 3 wherein a source terminal of said gain control FET is coupled to said input terminal of said amplifier.

5. The transimpedance amplifier of claim 1 wherein said amplifier includes two gain stages connected in series as a cascade.

6. The transimpedance amplifier of claim 5 wherein said two gain stages include a second gain stage that is a differential gain stage.

7. The transimpedance amplifier of claim 1 wherein said amplifier comprises GaAs FETs.

8. The transimpedance amplifier of claim 1 wherein said at least one gain stage includes an inductive load.

9. A method for maintaining the stability of a transimpedance amplifier including at least one gain stage having a controllable gain, a controllable variable impedance feedback branch, and a control circuit coupled to control the impedance of said controllable variable impedance feedback branch and the gain of said gain stage, said method comprising the step of, in response to an increase of the magnitude of input signal, reducing the impedance of the feedback branch and the gain of said gain stage.

10. The method of claim 9 wherein said controllable variable feedback branch comprises a feedback resistor connected in parallel with a feedback FET, and the reduction of the impedance of said feedback branch is accomplished by reducing the source-drain resistance of said feedback FET.

11. The method of claim 9 wherein said step of reducing the gain of said gain stage is accomplished by reducing a load impedance of said gain stage.

12. The method of claim 11 wherein said gain stage includes a gain control FET having a drain terminal coupled to an output node of said gain stage, and said step of reducing the load impedance of said gain stage is accomplished by reducing the source-drain resistance of said gain control FET.