Amplifier with modulated resistor gain control
First Claim
1. A circuit for controlling the gain of an amplifier operating over a prescribed frequency range having an input and an output comprising:
- means coupled to the output of the amplifier for generating a first signal representative of the output level of the amplifier,means for generating a second signal having predetermined waveform repeated at a rate greater than the reciprocal of twice the upper frequency of the prescribed frequency range;
means connected to the first and second signal generating means for forming a third signal having a level corresponding to the first signal and variations therefrom corresponding to the second signal;
means for generating a reference threshold; and
means connected to the amplifier responsive to the third signal and the reference threshold for determining the gain of the amplifier includingat least one switched impedance element; and
means jointly responsive to the third signal and said reference threshold for altering the value of the switched impedance element at the repetition rate of the second signal.
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Accused Products
Abstract
An automatic gain control circuit for an amplifier operating over a prescribed frequency range detects the output level of the amplifier; and couples a repeated predetermined waveform occurring at a rate greater than the reciprocal of twice the upper frequency of the prescribed frequency range to the output level signal. The waveform varying level signal is compared to a reference threshold to control the gain of the amplifier through a switched resistive elemement in the amplifier feedback path. The repeated waveform variations about the amplifier output level causes the value of the switched resistance to vary as a function of the output level. A low pass filter connected to the amplifier output removes switching transients resulting from the high frequency changes in the switched resistive element. The gains of a plurality of amplifiers may be determined by a common control for accurate tracking over a wide dynamic range.
161 Citations
27 Claims
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1. A circuit for controlling the gain of an amplifier operating over a prescribed frequency range having an input and an output comprising:
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means coupled to the output of the amplifier for generating a first signal representative of the output level of the amplifier, means for generating a second signal having predetermined waveform repeated at a rate greater than the reciprocal of twice the upper frequency of the prescribed frequency range; means connected to the first and second signal generating means for forming a third signal having a level corresponding to the first signal and variations therefrom corresponding to the second signal; means for generating a reference threshold; and means connected to the amplifier responsive to the third signal and the reference threshold for determining the gain of the amplifier including at least one switched impedance element; and means jointly responsive to the third signal and said reference threshold for altering the value of the switched impedance element at the repetition rate of the second signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. In a system having a plurality of amplifiers operating over a prescribed frequency range each having an input and an output, a common circuit for controlling the gains of the amplifiers comprising:
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means coupled to the output of each amplifier for generating a signal representative of the output level of the amplifier; means responsive to the level representative signals of the amplifiers for producing a combined amplifier level signal; means for generating a signal having a repeated predetermined waveform occurring at a rate greater than the reciprocal of twice the upper frequency of the prescribed frequency range; means connected to the output of the combined level signal producing means and the predetermined waveform signal generating means for forming a first signal having a level corresponding to the combined level signal and varying therefrom in accordance with the predetermined waveform signal; means for generating at least one reference threshold signal; and means responsive to the first signal and the reference threshold signals for determining the gains of the plurality of amplifiers including at least one switched impedance element in each amplifier; and means jointly responsive to the first signal and said reference threshold signals for altering the value of the switched impedance elements in each amplifier at the repetition rate of the predetermined waveform signal. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A signal amplifying circuit comprising:
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a plurality of amplifier stages connected in tandem, each amplifier stage including an amplifier operating over a prescribed frequency range having an input and an output and filtering means for limiting the amplifier output to the prescribed frequency range; means coupled to an output of the signal amplifying circuit for generating a signal representative of the output level of the signal amplifying circuit; means for generating a signal having a predetermined waveform repeated at a rate greater than the reciprocal of twice the upper frequency of the prescribed frequency range; means connected to the outputs of the level representative signal generating means and the predetermined waveform generating means for forming a first signal having a level corresponding to the level representative signal and varying therefrom according to the predetermined waveform signal; means for generating at least one reference threshold signal; and means responsive to the first signal and the reference threshold signals for determining the gain of each amplifier stage including at least one switched impedance element in each amplifier stage; and means jointly responsive to the first signal and said at least one reference threshold signal for altering the value of the switched impedance elements in each amplifier stage at the repetition rate of the predetermined waveform signal. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27)
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Specification