System for automatic tuning of an analogue filter

摘要

A DVB receiver including one or more digitally-tuneable lowpass filters in a direct baseband conversion stage. Tuning of the lowpass filters is achieved in a control loop, including a bandpass replica filter whose central frequency is locked to that of a reference oscillator. The topology of the replica filter is chosen so as to have a 90° shift at a reference frequency, and the error signal for the control loop is obtained by mixing input and output of the replica filter.