A tunable voltage controlled bandpass filter for a direct conversion receiver

摘要

A tunable voltage controlled bandpass filter 3 for a direct conversion receiver includes a phase locked loop which uses the phase change imparted by the bandpass filter 3 to local oscillator breakthrough from a mixer 4 for a measure of frequency difference between input RF and local oscillator 5 output. An error voltage derived from the measured phase change from a phase detector 10 is applied as a tuning control to the bandpass filter 3. A sample and hold arrangement 13 allows disconnection of the tuning circuit for power saving. The filter is suitable for implementation as an integral part of an ASIC receiver.