Dual loop automatic gain control
First Claim
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1. An automatic gain control (AGC) circuit comprising:
- an AGC loop including a first variable gain amplifier (VGA) and a second VGA; and
control circuitry for controlling respective amounts of gain applied by the first and second VGAs, the control circuitry comprising;
a first power monitor circuit, coupled to the first VGA for providing a first power level signal representing an average power level of an output signal of the first VGA;
a second power monitor circuit, coupled to the second VGA for providing a second power level signal representing an average power level of an output signal of the second VGA;
difference circuitry which generates first and second error signals representing respective differences between the first and second power level signals and first and second target signals, representing desired power levels for the output signals of the first and second VGAs respectively, anda combining circuit, responsive to the first and second error signals, which adjusts a total gain to be applied by the first and second VGAs and which determines a portion of the total gain to be applied by the first VGA and a portion of the total gain to be applied by the second VGA and distributes the total gain between the first and second VGAs in accordance with the determination;
wherein the control circuitry is responsive to an output signal of the AGC circuit to transfer gain from the second VGA to the first VGA to reduce a noise figure of the AGC circuit while maintaining the total gain.
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Abstract
An AGC circuit includes both wide-band and narrow-band VGAs. Two power monitors monitor the power level of the two VGAs. Based upon the signals provided by the power monitors, the AGC circuit derives two error terms. The AGC circuit filters and combines the error terms to determine a desired adjustment to the total gain and a desired adjustment to the distribution of the gain between the wide-band VGA and the narrow-band VGA. The AGC circuit also minimizes the noise figure of the narrow-band VGA subject to linearity constraints.
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Citations
16 Claims
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1. An automatic gain control (AGC) circuit comprising:
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an AGC loop including a first variable gain amplifier (VGA) and a second VGA; and control circuitry for controlling respective amounts of gain applied by the first and second VGAs, the control circuitry comprising; a first power monitor circuit, coupled to the first VGA for providing a first power level signal representing an average power level of an output signal of the first VGA; a second power monitor circuit, coupled to the second VGA for providing a second power level signal representing an average power level of an output signal of the second VGA; difference circuitry which generates first and second error signals representing respective differences between the first and second power level signals and first and second target signals, representing desired power levels for the output signals of the first and second VGAs respectively, and a combining circuit, responsive to the first and second error signals, which adjusts a total gain to be applied by the first and second VGAs and which determines a portion of the total gain to be applied by the first VGA and a portion of the total gain to be applied by the second VGA and distributes the total gain between the first and second VGAs in accordance with the determination; wherein the control circuitry is responsive to an output signal of the AGC circuit to transfer gain from the second VGA to the first VGA to reduce a noise figure of the AGC circuit while maintaining the total gain. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An automatic gain control (AGC) circuit comprising:
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a first variable gain amplifier (VGA), which amplifies a first signal occurring at a first point in the AGC circuit by an amount determined by a first gain control signal to produce a first amplified signal; a first power monitor, coupled to receive the first amplified signals for providing a first power signal, representing a measure of signal power for the first amplified signal; a second VGA, which amplifies a second signal occurring at a second point in the AGC circuit by an amount determined by a second gain control signal to provide a second amplified signal, wherein the second point in the circuit is distinct from the first point in the circuit and second signal has been amplified by the first VGA; a second power monitor, coupled to receive the second amplified signals for providing a second power signal, representing a measure of signal power for the second amplified signal; difference circuitry coupled to receive the first and second power signals and respective first and second target signals and which generates first and second error signals representing respective differences between the first and second power signals and the first and second target signals; and control circuitry, coupled to the first and second power monitors for receiving the first and second error signals and coupled to the first and second VGAs for providing the first and second gain control signals, the control circuitry including; combining circuitry, responsive to the first and second error signals for determining a total gain to be applied by the first and second VGAs, for determining a portion of the total gain to be applied by the first VGA and a portion of the total gain to be applied by the second VGA and for generating the first and second gain control signals.
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9. An automatic gain control (AGC) method for use in a AGC circuit that includes an AGC loop including a first variable gain amplifier (VGA) having an input signal and an output signal which is a function of the input signal and a first adjustable gain and a second VGA having an input signal and an output signal which is a function of the input signal of the second VGA and a second adjustable gain, the method comprising the steps of:
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monitoring the output signal of the first VGA to provide a first power level signal; monitoring the output signal of the second VGA to provide a second power level signal; generating first and second error sianals, representing respective differences between the first and second power level signals and first and second target signals; responsive to the first and second error sianals, determining an amount by which a sum of the first adjustable gain and the second adjustable gain are to be adjusted as a total gain adjustment; and responsive to the output signal of the second VGA, dividing the determined total gain adjustment between the first VGA and the second VGA to minimize the gain of the second VGA while maintaining the determined total gain adjustment, to reduce a noise figure of the output signal of the second VGA. - View Dependent Claims (10, 11, 12, 13, 14)
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15. A computer readable carrier including computer program instructions that cause a computer to implement an automatic gain control (AGC) method for use in a AGC circuit that includes an AGC loop including a first variable gain amplifier (VGA) having an input signal and an output signal which is a function of the input signal and a first adjustable gain and a second VGA having an input signal and an output signal which is a function of the input signal of the second VGA and a second adjustable gain, the method comprising the steps of:
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monitoring the output signal of the first VGA to provide a first power level signal; monitoring the output signal of the second VGA to provide a second power level signal; generating first and second error signals, representing respective differences between the first and second power level signals and first and second target signals; responsive to the first and second error sianals, determining an amount by which a sum of the first adjustable gain and the second adjustable gain are to be adjusted as a total gain adjustment; and dividing the determined total gain adjustment between the first VGA and the second VGA to minimize the gain of the second VGA. - View Dependent Claims (16)
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Specification