Siliconsystems, Inc.

Paul Hurst

Steve Levy

Dave Hedberg

Kiyoshi Fukahori

The present invention is directed to a digital non-coherent pattern detection scheme in which spectral analysis of phase encoded signals is utilized to provide pattern recognition. The present invention is relatively insensitive to the power level of incoming signals. Since the power level is easily detected and determined, the present invention allows the various algorithms to operate quickly. Further, utilizing the magnitude samples of the incoming signal result in a pattern detection scheme that is independent of modulation technique. The present invention utilizes the concept of spectral analysis to determine spectral lines which are present in phase encoded signals. A phase encoded signal such as a DPSK or QAM having an implicit pattern contained therein, which results in unique spectral lines. By detecting the spectral lines in certain combinations, the phase encoded pattern being sent may be identified. For example, 'unscrambled mark', 'S1', and other patterns may be identified using the method of the present invention. In operation, a plurality of receive channels are implemented to detect energy levels at specific frequencies and thereby identify spectral lines. The input signal is demodulated with one of a plurality of modulating frequencies F.sub.0 -F.sub.n in each receive channel, chosen to translate the input spectra signal to baseband. The demodulated signal is low pass filtered and the filtered output is squared, generating a power signal. In the preferred embodiment, the power signal is filtered again to obtain a stochastic average. This averaged signal is coupled to an energy detect block. If energy at the desired spectra is present and of sufficient magnitude, a digital 'one' is provided as output, if sufficient energy is detected, a digital 'zero' is provided as output. A logical 'one' is provided at the output representing the specific pattern detected as indicated by the digital word.

Non-coherent pattern detection

A synchronous timer anti-alias filter gain stage utilizing switched capacitor circuitry is described. A high frequency sampling clock is used for a switched capacitor anti-alias filter. In the preferred embodiment, a clock of approximately 921.6 kilohertz is utilized. This fast clock is divided down by a programmable timer into a low frequency sampling clock to drive a signal gain stage. The programmable divide values are integers so that the anti-alias filter clock and gain stage clock are in an integer relationship with each other for edge locking. The high frequency clock is divided down by a fixed divider to provide a clocking signal to an input band pass filter. The fixed divide value is also an integer so that the band pass filter clock and anti-alias filter clock are in integer relationship with each other. Switched capacitor anti-alias filters are used in place of continuous time, R-C anti-alias filters. The switched capacitor anti-alias filter has greater accuracy than R-C filters, approaching the range of 0.2% accuracy of the time constant. In addition, the switched caapcitor anti-alias filter requires less silicon area than equivalent R-C filters in integrated cirucit implementations. DC offsets are eliminated by preceding and following the gain stage by first order high pass filters. The programmability of the low frequency sampling clock rate, by changing the divide values, allows the received baud rate to be tracked in modem applications.

Synchronous timer anti-alias filter and gain stage

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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Yolo, CA, United States of America

Paul Hurst