04972436 is referenced by 163 patents and cites 7 patents.

An improved analog front end circuit for a high performance modem comprising an oversampling sigma delta modulator analog-to-digital converter which employs a novel four phase clocked MOSFET switched capacitor integrator. The integrator is switched in a manner as to eliminate signal dependent charges in the MOSFET switches. The sigma delta modulator shifts quantization noise of the analog-to-digital conversion process out of baseband of the analog signal. A novel integrated decimating FIR low pass filter filters the quantization noise from the digital output signals, and reduces the number of digital signals to obtain a sufficient number of signal samples in order to provide operation at high speeds, for example 9600 bps. The improved four phase switched capacitor integrator is also suitable for use in sigma delta modulator circuits, analog-to-digital converter circuits, integrating cirucits, and the like. A novel return-to-zero circuit eliminates distortion in a sigma delta modulator based analog-to-digital conversion process which can result from unequal rise and fall times of the digital output, by insuring that the energies in signals represented by a "one" and signals represented by a "zero" are equal, even during portions of the bit stream wherein there is a consecutive sequence of "ones".

Title
High performance sigma delta based analog modem front end
Application Number
7/257733
Publication Number
4972436
Application Date
October 14, 1988
Publication Date
November 20, 1990
Inventor
Randy D Nash
Dacula
GA, US
Raouf Y Halim
Alpharetta
GA, US
Agent
Jones Askew & Lunsford
Assignee
Hayes Microcomputer Products
GA, US
IPC
H04B 14/06
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