Demodulation circuit for unknown channel property wave - has adaptive phase corrector in digital hilbert filter pair

摘要

Already in Patent Appl. P3006801 a synchronous demodulation receiver has been described in which analogue signals derived from a band pass channel are regenerated and transformed into analytical signals by means of a Hilbert filter pair. In present this filter pair is made also adaptive, that is, self-adjusting to the parameters of the received signal. This is obtained by a phase subtractor member producing the error vectors and quadrant error derived from the vectorial output signals (zp, zq) derived from the Hilbert filter pair summing circuits. The identified error vectors are utilised for modifying the coefficient input signal (h/p-n, h/q-n) to the multipliers whose other inputs derive from the amplitude-sampled wave form segments in the delay stages (T/1). The continually varying multiplication coefficient derives its sign from an algorithm connecting the sampling clock interval (T), the index (i) of the clock pulse sequence, the adaptor factor for the sample step width, the input signal sequence (u) the difference vector (z-q) the vectors at the input and output of the so called decision circuit (Es), and the carrier frequency (f).