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CACD Group updated 2000.11.30 Author Janez Puhan |
Synchronous DemodulatorThe circuitTo decode a message in amplitude modulated carriers, a waveform has to be multiplied with itself using a product demodulator. In many ways, a simple nonlinear device like a semiconductor diode can be used for this purpose. Its exponential characteristic can be mathematically expressed by a Taylor series. The message then is decoded by filtering out the quadratic term. In applications like spectrum analysers and lock-in amplifiers, problems with higher order Taylor terms may occur. In this case, the diode should be replaced with a device having a parabolic characteristic, a junction field effect transistor for example. However, in zero-IF systems, dc terms have to be eliminated too. This is the area of synchronous demodulators.
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