Frequency tracking filter, signal processing circuit with tunable transconductance and mehtod of controlling a transconductance circuit

摘要

Spurious energy suppression for a data communication system is achieved without using a large order noise suppression filter, by means of a post-mixer tracking filter that contains a current-controlled MOSFET-implemented resistance (153) for a transconductance-capacitance filter and an associated transconductance tuning stage. The MOSFET-implemented resistance (153) is controlled by the same control current (150) that establishes the output frequency. As a result, the cut-off frequency of the tracking filter is linearly proportional to the carrier and independent of absolute processing parameters and temperature.