AM digital demodulation methods
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From: HardySpicer on 27 Apr 2010 02:51 On Apr 26, 3:59 am, Vladimir Vassilevsky <nos...(a)nowhere.com> wrote: > Jerry Avins wrote: > > If synchronous demodulation loses the signal > > even when I/Q demodulation tracks it, in what way is synchronous > > demodulation superior? Have you had a chance to compare the outputs of > > the two detectors when both are working? > > BTW, in the modern ICs, they demodulate AM in a quasi-synchronous way: > the bandpass signal is digitized by comparator and the output of the > comparator drives the analog switch which does synchronous > rectification. The advantage is much better linearity compared to diode > detector. Obviously this could be improved by adding a narrowband filter > in front of the comparator; however it is not worth extra cost for > consumer applications. > > Vladimir Vassilevsky > DSP and Mixed Signal Design Consultanthttp://www.abvolt.com Could all be done with an op-amp! What nonsense. How to make radio 1000 times more complicated than it need be. Hardy
From: steveu on 27 Apr 2010 04:05
>On Apr 26, 3:59=A0am, Vladimir Vassilevsky <nos...(a)nowhere.com> wrote: >> Jerry Avins wrote: >> > If synchronous demodulation loses the signal >> > even when I/Q demodulation tracks it, in what way is synchronous >> > demodulation superior? Have you had a chance to compare the outputs of >> > the two detectors when both are working? >> >> BTW, in the modern ICs, they demodulate AM in a quasi-synchronous way: >> the bandpass signal is digitized by comparator and the output of the >> comparator drives the analog switch which does synchronous >> rectification. The advantage is much better linearity compared to diode >> detector. Obviously this could be improved by adding a narrowband filter >> in front of the comparator; however it is not worth extra cost for >> consumer applications. >> >> Vladimir Vassilevsky >> DSP and Mixed Signal Design Consultanthttp://www.abvolt.com > >Could all be done with an op-amp! What nonsense. How to make radio >1000 times more complicated than it need be. Vlad described a solution consisting of a comparator (i.e. an op-amp with op-amp crossed out, and comparator written across it in crayon) and an analogue switch (i.e. one of the simplest structures in mixed signal CMOS). Your solution requires an op-amp and a diode. Can you explain the 1000 times complexity ratio? Steve |