Frequency and time domain adaptive filtration in a sampled communication

Abstract

Apparatus for performing time and frequency-domain filtering in a sampled communication channel for the transmission of binary information. A received signal is provided to a double-domain, analog transversal equalizer comprising a plurality of serially connected, active, analog filter sections with associated tap locations, each filter section having a programmable frequency response and adaptively controlled one-bit delay. The filter sections provide sequential, cumulative frequency domain filtering as the received signal propagates through the equalizer. The transfer function of each filter section has a linear phase polynomial denominator and a real (at s=j.omega.) polynomial numerator, facilitating independent control of the delay and frequency response of each filter section. A plurality of analog multipliers multiply signals present at the tap locations by analog tap weight signals to generate a plurality of product signals, and an analog summer adds the product signals to generate an output filtered signal before sampling occurs. An LMS error-based adaptive tap weight control circuit iteratively generates optimal analog tap weight signals, a delay control circuit provides the necessary timing signals at the bit-rate to control the time delay of each analog filter section and a location of zeros circuit controls the location of zeros in the transfer function, and hence the frequency response, of each filter section. The double-domain transversal equalizer provides aperiodic and controlled frequency response at low frequencies and does not require a noise suppressing prefilter.