| 摘要 |
In an improved demodulator, which is primarily applicable to the demodulation of angle modulated signals with a poor carrier-to-noise ratio (e.g. satellite TV signals received with a small aperture dish antenna), an intermediate frequency stage (20) is coupled to a differential phase circuit (48,50,52,54) in which delayed in-phase and quadrature components of the intermediate frequency signal are multiplied with the intermediate frequency signal itself to generate a pair of baseband differential phase quadrature signal components having a reduced noise content.These differential phase quadrature signal components are than averaged by filters (56,58) to further improve the signal to noise ratio, and then digitized and fed as digital samples to a PROM circuit (38) which performs an inverse tangent operation to derive a demodulated digital signal representative of the angle modulation phi , where cos phi and sin phi are the differential phase components. Impulse noise is minimized by carrying out the differential phase and averaging operation prior to the nonlinear inverse tangent operation. The invention also includes the technique of mixing signal components which are delayed relative to each other by a time greater than or equal to 0.25/B, where B is the IF signal bandwidth, to achieve further impulse noise reduction.
|
