| 摘要 |
<p>A quadrature demodulator for deriving an in-phase (I) and quadrature (Q) component from an input RF signal comprises means (24,25) for down-converting the RF signal to an IF signal. The IF signal is sampled (27) and digitised by an ADC (28). A complex digital filter (29) is used as a phase splitter designed to pass the positive IF frequency +f0 but block the negative IF frequency -f0. The resultant complex signal is in IQ form. By using four times oversampling at the ADC (28) the digital filter (29) can be split cleanly into two smaller filter sections (30, 31). By using feedforward filters for both these filter sections (30 and 31) a high degree of phase linearity can be achieved with minimal distortion. <IMAGE></p> |
