Matsushita Electric Industrial Co., Ltd.

Shigeru Soga

Daisuke Hayashi

Takaya Hayashi

Seiji Sakashita

Toshihiko Fukuoka

Hiroshi Saka

Kazunao Urata

Integrating AFC/APC function with waveform equalization function for and reducing the circuit size of a signal wave-form equalizer apparatus. A waveform equalization section is divided into an FFE block as an anterior stage and a DFE block as a posterior stage. An AFC/APC block is provided therebetween. In the AFC/APC block, an AFC/APC coefficient update section updates a coefficient used for removing frequency and phase errors in accordance with an LMS algorithm, and a tap multiplies a modulated signal by the updated coefficient. Error data produced by an error estimation block is used by not only FFE and DFE coefficient update sections but also the AFC/APC coefficient update section for updating the coefficients. That is to say, the waveform equalization section and the AFC/APC block use the error estimation block in common, thereby reducing the circuit size considerably.

Signal waveform equalizer apparatus

A QPSK modulation signal is processed with frequency conversion into an IF signal by a channel selection circuit, and then is converted into a baseband signal by a quadrature demodulator. The baseband signal has a wave thereof shaped by DTFs and then sent to a carrier recovery circuit. An offset frequency of the IF signal detected by an AFC circuit is compensated for by a baseband frequency converter including a complex multiplier and a DVCO. The frequency tracking circuit detects whether an operating frequency of another DVCO in the carrier recovery circuit goes beyond a range. By tracking an oscillation frequency of the DVCO in the baseband frequency converter so as not to go beyond the reference value, frequency deviation of the spectrum of signals which are input to the DTFs is controlled not to go beyond the reference value. By offsetting a frequency dividing ratio of a variable frequency divider of the channel selection circuit by an amount corresponding to the offset frequency of the IF signal detected by the frequency detector, the frequency deviation of the QPSK modulation signal can be compensated for whichever channel is selected.

Demodulation apparatus performing different frequency control functions

A demodulation method for tentatively demodulating a modulated input signal by a signal having a fixed frequency to form a tentative complex demodulated signal and then generating a determined complex demodulated signal from the tentative complex demodulated signal. The method includes step (a) of obtaining a determined complex demodulated signal by compensating for the tentative complex demodulated signal based on an optimum phase compensation amount; step (b) of estimating an optimum frequency compensation amount based on a shift in the optimum phase compensation amount during a predetermined cycle; and step (c) of estimating an immediately subsequent optimum phase compensation amount to be used in the steps (a) and (b) performed in repetition, based on the tentative complex demodulated signal, the determined complex demodulated signal, and the optimum frequency compensation amount.

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Matsubara, Japan

Shigeru Soga