Digital AM demodulator

摘要

The demodulator includes a source (1) for producing digitised signals (bf) from an amplitude-modulated signal (hf). A sampling clock (ts) is used, whose sampling frequency is higher than the sum of twice the frequency of a carrier contained in the AM signal, and four times the usage signal bandwidth. The output of the source is fed to a squarer (2) and the squared signal (q) is fed to a low pass filter (3) whose passband is at least as large as twice the bandwidth of the usage signal, but smaller than the difference between twice the carrier frequency and twice the usage signal bandwidth. In the case of a folded back, double carrier frequency, the passband of the low pass filter is at least as large as twice the usage signal bandwidth, but smaller than the difference between a folded back, double carrier frequency and twice the usage signal bandwidth. A digital square root generator (4) forms a square root value (r) from the output of the low pass filter, as an output signal which corresponds to the amplitude of the usage signal in the AM signal.