Shared resources modulator-demodulator circuits for use with qua

Details Shared resources modulator-demodulator circuits for use with qua Shared resources modulator-demodulator circuits for use with qua

1995-11-07

1997-11-25

Chin, Wellington

Pulse or digital communications

Systems using alternating or pulsating current

Angle modulation

375219, 375222, 375298, 375321, 329304, 332103, H04L 2710

Patent

active

056920130

ABSTRACT:
A common transceiver circuit for use as either a modulator or demodulator and that is implemented through a shared resource approach. This approach is particularly, though not exclusively, suited for with quadrature amplitude modulated (QAM) or vestigial sideband (VSB) signals. Specifically, a QAM transceiver circuit (400), through strategically located multiplexing stages, physically re-uses both a complex Nyquist filter (310, 320) and an equalizer (140) for demodulation and modulation. Additionally, tap coefficients of the complex Nyquist filter are set such that a center frequency of an otherwise baseband Nyquist filter is translated upward to a symbol rate in order to eliminate a separate complex mixer (250, 260). Similarly, a VSB transceiver circuit (700), also through strategically located multiplexing stages, physically re-uses a complex vestigial Nyquist filter (610), a complex mixer (620) and an equalizer (785) during demodulation and modulation. The VSB transceiver also selects a particular configuration of a common complex Hilbert transform circuit (720) for use during either demodulation or modulation. In either transceiver, the same equalizer selectively provides both channel equalization, during de-modulation, and (sin x)/x compensation, during modulation, through use of differing corresponding sets of tap coefficients.

REFERENCES:
patent: 5259000 (1993-11-01), Kojima et al.
patent: 5633891 (1997-05-01), Rebec et al.
Draft Report, VSB Transmission System--Grand Alliance, Technical Details; Dec. 7, 1994.

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