H - Electricity – 04 – L
Patent
H - Electricity
04
L
H04L 27/18 (2006.01) H03J 7/06 (2006.01) H04L 27/22 (2006.01)
Patent
CA 2101592
ABSTRACT OF THE DISCLOSURE A frequency stabilizing circuit for a .pi./4 QPSK (Quadrature Phase Shift Keying) signal receiver has a voltage controlled oscillator (VCO) for outputting an oscillation signal whose frequency changes in response to a control voltage applied to the VCO. A mixer changes the frequency of an input .pi./4 shift QPSK signal. A counter measures the frequency of the .pi./4 shift QPSK signal from the mixer. A timing generator generates, on the basis of the oscillation signal from the VCO, a timing indicative of an interval during which the counter is to measure the frequency. A set data generator generates a frequency signal having a predetermined set frequency. A comparator compares the frequency measured by the counter and the set frequency of the set data generator to thereby output the resulting frequency deviation. A voltage data generator changes voltage data in association with the frequency deviation. A digital-to-analog converter transforms the voltage data to the control voltage. A demodulator demodulates the .pi./4 shift QPSK signal from the mixer. An integrator adds up phase s h i f t s output from the demodulator over the interval generated by the timing generator. An adder/subtracter selectively increases or decreases the set frequency of the frequency signal output from the data generator in association with a cumulative phase shift produced by the integrator. The circuit is capable of stabilizing the frequency of a .pi./4 shift QPSK signal receiver even when the mean frequency differs from the carrier frequency due to the offset of data.
Corporation Nec
Smart & Biggar
LandOfFree
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