US 5,692,013 A · Shared resources modulator-demodulator circuits for use with quadrature amplitude modulated signals

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.

Claims30

Dependent claims

Apparatus for a quadrature amplitude modulated (QAM) demodulator/modulator comprising:

a complex multi-function filter, commonly used during QAM modulation and QAM demodulation and responsive to both an input signal and a mode signal, to provide an output filtered signal, wherein the multi-function filter imparts a different pre-defined function to the input signal corresponding to a current state of the mode signal;
the mode signal being either in a pre-defined first or second state signifying QAM demodulation or QAM modulation, respectively;
wherein the filter, during QAM demodulation and in response to the first state of the mode signal, equalizes the input signal such that the output filtered signal is an equalized version of the input signal, and the filter, during QAM modulation and in response to the second state of the mode signal, imparts a pre-defined frequency response characteristic to the input signal such that the output filtered signal is a frequency compensated version of the input signal;
and
a first multiplexor, responsive to the mode signal, for selectively routing as the input signal to the complex multi-function filter either, during QAM demodulation, a complex Nyquist filtered QAM modulated signal or, during QAM modulation, Nyquist filtered symbols.

2 more elements

Apparatus for a repeater for quadrature amplitude modulated (QAM) digital signals comprising:

first and second transceiver circuits, wherein the first transceiver circuit demodulates a stream of incoming modulated digital QAM symbols so as to produce a stream of complex digital decisions and the second transceiver circuit modulates said decisions so as to produce an output QAM modulated signal, each of said first and second transceivers comprising:
a complex multi-function filter, commonly used during QAM modulation and QAM demodulation and responsive to both an input signal and a mode signal, to provide an output filtered signal, wherein the multi-function filter imparts a different pre-defined function to the input signal corresponding to a current state of the mode signal;
the mode signal being either in a pre-defined first or second state signifying QAM demodulation or QAM modulation, respectively;
wherein the filter, during QAM demodulation and in response to the first state of the mode signal, equalizes the input signal such that the output filtered signal is an equalized version of the input signal and, during QAM modulation and in response to the second state of the mode signal, imparts a pre-defined frequency response characteristic to the input signal such that the output filtered signal is a frequency compensated version of the input signal;
and
a first multiplexor, responsive to the mode signal, for selectively routing as the input signal to the complex multi-function filter either, during QAM demodulation, a complex Nyquist filtered QAM modulated signal or, during QAM modulation, Nyquist filtered symbols.

3 more elements

Dependencies are inferred from the claim text.

Shared resources modulator-demodulator circuits for use with quadrature amplitude modulated signals

Life of this patent

Shared resources modulator-demodulator circuits for use with quadrature amplitude modulated signals

Life of this patent

Abstract

Claims30