Self-tuning bandstop filter - has compensating voltage controlled by phase comparator to bring output voltage to zero irrespective of frequency setting

摘要

The self-tuning bandstop filter automatically brings its residual output voltage down to zero irrespective of the frequency setting. The filter is tuned without range switching and without intervention by hand. The second-order active filter network (1) has both a bandstop output (3) and a bandpass output (4). A bipolar gain-controlled amplifier (8) is connected to the bandpass output and passes a compensating voltage to an adder (9) coupled to the bandstop output. The amplitude and polarity of this compensating voltage are controlled by a phase comparator (7) that receives equal phased inputs when the filter is tuned.