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

• US 6,107,878 A
• Filed: 08/06/1998
• Issued: 08/22/2000
• 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): Mottola, Steven J.
• Application Number:
  US09/130,393
• Time in Patent Office: 747 Days
• Field of Search: 330/51, 330/129, 330/133, 330/134, 330/279, 455/234.1, 455/241.1, 455/242.2, 455/245.1, 455/245.2, 455/251.1, 455/253.1, 455/253.2
• 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:

linear gain control means for producing a first variable gain value in response to an overall gain value whereby;

said first variable gain value is zero while the overall gain is less than a first predetermined threshold;

said first variable gain value increases linearly with the overall gain while the overall gain is greater than said first predetermined threshold; and

said first variable gain value ceases to increase once it has reached a predetermined maximum gain level;

step gain control means for producing a constant gain control signal and a constant gain value in response to an overall gain value whereby;

said constant gain control signal is off and said constant gain value is zero while the overall gain is less than a second predetermined threshold;

said constant gain control signal is on and said constant gain value is a predetermined constant gain level while the overall gain is greater than a third predetermined threshold; and

said constant gain control signal is subject to hysteresis between off and on and said constant gain value is subject to hysteresis between zero and said predetermined constant gain level while the overall gain is between said second predetermined threshold and said third predetermined threshold;

adder means for producing a second variable gain which is the sum of;

the overall gain value;

the negative of said predetermined constant gain level when said constant gain control signal is on; and

the negative of said first variable gain value.

3. The apparatus of claim 1 wherein said constant gain control signal can be programmably overriden to be off or on.

6. The apparatus of claim 1, further comprising:

a filter for filtering said overall gain control value;

a first mux to select between said overall gain control value and the output of said filter for input to said step gain control means;

a second mux to select between said overall gain control value and the output of said filter for input to said linear gain control means.

8. The apparatus of claim 3, further comprising:

a filter for filtering said overall gain control value;

a first mux to select between said overall gain control value and the output of said filter for input to said step gain control means;

a second mux to select between said overall gain control value and the output of said filter for input to said linear gain control means.

2. An apparatus for gain control comprising:

linear gain control means for producing a first variable gain value in response to an overall gain value whereby;

said first variable gain value is zero while the overall gain is less than a first predetermined threshold;

said first variable gain value increases linearly with the overall gain while the overall gain is greater than said first predetermined threshold; and

said first variable gain value ceases to increase once it has reached a predetermined maximum gain level;

step gain control means for producing a constant gain control signal and a constant gain value in response to an overall gain value whereby;

said constant gain control signal is off and said constant gain value is zero while the overall gain is less than a second predetermined threshold;

said constant gain control signal is on and said constant gain value is a predetermined constant gain level while the overall gain is greater than a third predetermined threshold; and

said constant gain control signal is subject to hysteresis between off and on and said constant gain value is subject to hysteresis between zero and said predetermined constant gain level while the overall gain is between said second predetermined threshold and said third predetermined threshold;

first adder means for producing the sum of said constant gain value and programmably selected zero or said first variable gain value; and

second adder means for producing a second variable gain which is the sum of the overall gain value and either the negative of the output of said first adder means when said constant gain control signal is on or zero when said constant gain control signal is off.

4. The apparatus of claim 2 wherein said constant gain control signal can be programmably overriden to be off or on.

7. The apparatus of claim 2, further comprising:

a filter for filtering said overall gain control value;

a first mux to select between said overall gain control value and the output of said filter for input to said step gain control means;

a second mux to select between said overall gain control value and the output of said filter for input to said linear gain control means.

9. The apparatus of claim 4, further comprising:

a filter for filtering said overall gain control value;

a first mux to select between said overall gain control value and the output of said filter for input to said step gain control means;

a second mux to select between said overall gain control value and the output of said filter for input to said linear gain control means.

5. An apparatus for gain control comprising:

step control means for producing a gain stage bypass control signal in response to an overall gain value;

linear gain control means for producing a first variable gain control value in response to said overall gain value;

adder means for producing a second variable gain control value as the difference between said overall gain value and any gain introduced under control of said step control means and said linear gain control means.

10. The apparatus of claim 5, further comprising:

a filter for filtering said overall gain control value;

a first mux to select between said overall gain control value and the output of said filter for input to said step gain control means;

a second mux to select between said overall gain control value and the output of said filter for input to said linear gain control means.