US 5,297,184 AGranted

Gain control circuit for synchronous waveform sampling

AssigneeCirrus Logic, Inc.

InventorsRichard T. Behrens, Trent Dudley, Neal Glover

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Abstract

A mixed analog and digital gain control circuit for controlling the amplitude of an analog input signal. The circuit has a variable gain amplifier that receives the signal from a read/write recording head preamplifier. The output of the variable gain amplifier is connected through a multiplexer and equalizer to an analog to digital converter for converting the analog signal to digital sample values at controlled sampling times. A gain control circuit receives the digital values and the output of a pulse detector indicating when a pulse has occurred. A gain error detector within the gain control circuit determines the amount of error in the amplitude of each detected pulse, and this error amount is filtered and sent through a digital to analog converter and then through an exponentiating circuit. The output of the exponentiating circuit is connected to a gain control input of the variable gain amplifier.

Claims17

Dependent claims

A gain control circuit for adjusting the gain of a variable gain amplifier that receives an analog signal, to cause an output of said variable gain amplifier to have a predetermined signal level at an occurrence of a pulse, said gain control circuit comprising:

amplitude sampling means for receiving said analog signal and for taking a plurality of amplitude samples of an amplitude of said analog signal, said amplitude samples being taken at times determined by a clock signal;
pulse detection means connected to receive said plurality of amplitude samples, wherein said pulse detection means determines whether a pulse occurred coincident with each of said plurality of amplitude samples;
sample selection means connected to an output of said amplitude sampling means and an output of said pulse detection means, said sample selection means for selecting, for each pulse detected by said pulse detection means, at least one of said plurality of amplitude samples, wherein said at least one amplitude sample has a predetermined relationship to a location of said pulse;
arithmetic means for comparing said at least one selected amplitude sample to a predetermined value and for creating an amplitude error measurement signal representative of a difference in amplitude between said at least one selected amplitude sample and said predetermined value;
and
conversion means connected between said arithmetic means and a gain control input of said variable gain amplifier, said conversion means for receiving said amplitude error measurement signal and converting said amplitude error measurement signal into a gain control signal connected to said gain control input.

3 more elements

A gain error detector circuit that receives a plurality of amplitude samples of an input signal, and receives a plurality of pulse indicators, one pulse indicator corresponding to each of said amplitude samples, wherein said pulse indicator indicates whether a pulse occurred at said corresponding amplitude sample, said gain error detector circuit comprising:

sample selection means connected to receive said amplitude samples and further connected to receive said pulse indicators, said sample selection means for selecting, for each pulse indicator that indicates a pulse occurred, at least one of said plurality of amplitude samples, wherein said at least one amplitude sample has a predetermined relationship to said pulse indicator;
arithmetic means for comparing said at least one selected amplitude sample to a predetermined value and for creating an amplitude error measurement signal representative of a difference in amplitude between said at least one selected amplitude sample and said predetermined value;
and
filter means connected to said amplitude error measurement signal for converting said amplitude error measurement signal to a gain error signal.

1 more element

Dependencies are inferred from the claim text.