Automatic gain control circuit for controlling multiple variable gain amplifier stages while estimating received signal power

• US 6,181,201 B1
• Filed: 10/11/1999
• Issued: 01/30/2001
• Est. Priority Date: 08/06/1998
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Black, Peter J.
• Primary Examiner(s): Shingleton, Michael B
• Application Number:
  US09/417,204
• Time in Patent Office: 477 Days
• Field of Search: 330/129, 330/133, 330/134, 455/241.1, 455/245.2, 455/247.1, 455/253.2, 455/253.1
• US Class Current: 330/129
• CPC Class Codes: H03G 3/3078 Circuits generating control signals for digitally modulated signals
• CPC Class Codes: H04B 1/109 by improving strong signal performance of the receiver when strong unwanted signals are present at the receiver input

Abstract

The present invention is a novel and improved AGC circuit which is generically configurable to accommodate a variety of AGC amplifier configurations to enhance IP3 performance and reduce required amplifier current, while providing a received power estimate which remains valid regardless of how the gain or attenuation is distributed among the various amplifiers. A generic control circuit maintains this power estimate in a single overall gain amplification value by distributing gain to at least two amplifier stages in response to that value. By programming or hard coding a few key parameters, a generic control circuit can control a wide variety of amplifier configurations. Among the configurations supported are switched LNA, switched variable gain LNA, variable gain, and a decoupled IF and UHF variable gain LNA configuration. The invention is extendable to include multi-stage amplifier configurations. Although the preferred embodiment includes two stages, one for UHF and one for IF, three or more stages can easily be adapted. Various filtering schemes can be applied to the power estimate to tailor the temporal dynamics of gain switching. For example, a low pass filter can be applied to the UHF front end to give it a slower response than the IF stage. All of these configurations and any subset can be supported in a single generic device.

Claims

1. An apparatus for gain control comprising:

a plurality of gain control means for producing a plurality of gain values in response to an overall gain value;

adder means for producing an additional gain value which is the difference of the overall gain value and the sum of said plurality of gain values.

2. A method for gain control comprising:

producing a plurality of gain values for a plurality of gain control means in response to an overall gain value;

producing an additional gain value by subtracting of the sum of said plurality of gain values from the overall gain value.