Quadrature amplitude modulator using switched capacitor filter
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United States of America Patent
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-
Oct 11, 1988
Grant Date -
N/A
app pub date -
May 1, 1987
filing date -
May 1, 1987
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A switched capacitor circuit implements a base band, finite impulse response filter (BBF) and balanced modulator with a single operational amplifier. The analog modulator has particular application in voice band modem applications and requires little or no microprocessor code space. Simplified sine and cosine functions are implemented in a pair of base band filters such that the output of only one base band filter is required at any one time. In this manner, a single operational amplifier may be utilized to implement the analog modulator/base band filter of the present invention. The use of switched capacitor technology and a single operational amplifier results in less silicon area dedicated to the analog modulator than for corresponding digital modulators.
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