Quality factor tuning system for a tunable filter and current rectifier used therein

Tuning system for generating a tuning signal (VTQ) to be applied to at least one master tunable filter in order to tune the quality factor of the master tunable filter to substantially equal a desire quality factor value, the tuning system comprising:

• a tunable filter which is a replica of the master tunable filter, said tuning signal also being applied to said tunable filter (BIQUAD) in order to tune the quality factor of said tunable filter to substantially equal said desired quality factor value, the damping of said tunable filter being controlled in response to changes in said tuning signal;
• means for providing a reference signal;
• first means responsive to said reference signal for providing a first output signal (IO1) indicative of said reference signal multiplied by a first gain (Z1);
• said tunable filter being responsive to said reference signal for providing a tunable filter output signal (VO) indicative of said reference signal multiplied by the passband gain of said tunable filter;
• second means responsive to said tunable filter output signal (VO) for providing a second output signal (IO2) indicative of said tunable filter output signal multiplied by a second gain (Z2);
• wherein the ratio of said first gain to said second gain is indicative of a desired gain value, the value of said desired gain value being equal to the value of the passband gain of said tunable filter corresponding to said desired quality factor value;
• and
• difference means (CM), responsive to said first and second output signals for providing a tuning system output signal which is a function of the difference of said first and second output signals from which said tuning signal (VTQ) is derived, wherein said tuning signal (VTQ) is provided as negative feedback to said tunable filter to change the magnitude of said passband gain to substantially equal said desired gain value.