Apparatus and method for combining analog and digital automatic gain control in receivers with digital signal processing
AssigneeCubic Communications, Inc.
InventorRichard N. Jekel
Life of this patent
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Abstract
Two automatic gain control (AGC) loops are connected by a feedforward signal. An intermediate frequency (IF) filter may be located between the output of the front-end loop and the input of the back-end loop. Stability and responsiveness are improved because neither AGC loop includes a narrowband filter. The front-end loop may include an analog gain-controlled element, but the remainder of the invention may be implemented digitally. The front-end loop prevents overloading of the A/D converter that feeds the gain-controlled signal to the remainder of the invention, and the back-end loop compensates for actions taken in the front-end loop.
Claims30
An automatic gain control system, comprising:
- a first automatic gain control (AGC) loop for receiving an input signal, for producing a first gain controlled-signal, and for producing a first control signal in response to said first gain-controlled signal, said first gain-controlled signal produced in response to said input signal and said first control signal;
- a filter for filtering said first gain-controlled signal and for providing a filtered first gain-controlled signal;
- and
- a second automatic gain control (AGC) loop for producing a second gain-controlled signal and for producing a second control signal in response to said second gain-controlled signal and said first control signal, said second gain-controlled signal produced in response to said filtered first gain-controlled signal and said second control signal.
An automatic gain control system, comprising:
- a first automatic gain control (AGC) loop having a bandwidth, said first AGC loop for receiving a radio frequency input signal and for producing an intermediate frequency (IF) first gain-controlled signal;
- an IF filter having a bandwidth wider than said bandwidth of said first AGC loop, said IF filter for receiving said first gain-controlled signal and for producing a filtered first gain-controlled signal;
- and
- a second automatic gain control (AGC) loop having a bandwidth narrower than said bandwidth of said first AGC loop, said second AGC loop for receiving said filtered first gain-controlled signal and for producing a second gain-controlled signal.
A method for providing automatic gain control in a receiver having digital signal processing circuitry, comprising the steps of:
- detecting the amplitude of an input signal and producing a first gain signal in response to said detection;
- controlling said amplitude of said input signal in response to said first gain signal;
- providing a digital signal having said controlled amplitude to a digital intermediate frequency (IF) filter;
- detecting the amplitude of a filtered signal and producing a second gain signal in response to said detection;
- and
- controlling said amplitude of said filtered signal in response to said first and second gain signals.
Dependencies are inferred from the claim text.