Could some electronics guru please provide some hints to my queries. For a 'four-times' carrier frequency recovery scheme, as used in QPSK, the QPSK signal is fed into a 'power-4' circuit, that outputs the fourth power of the input QPSK signal. This output is fed into a band-pass filter, whose center frequency is 4 times the frequency of the QPSK carrier signal. A band-pass filter obviously has a bandwidth - so in this case, how should the output of the bandpass filter look like ? Any hints, suggestions would be useful. Thanks in advance.
Some questions regarding band-pass filters
Jan 14, 2011
2 Replies
Why, like a sinusoid at four times the carrier frequency, of course. What else could it be?
Jeroen Belleman
I'm not familiar with that scheme, but rectification of the data followed by a high-Q bandpass is a common clock recovery scheme. IIRC, they use a biquad. The bandpass output and lowpass output are in quadrature, which should give you enough edges.
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