Corrective circuit for an active narrow notch filter

Claim 2

A corrective circuit for an active band-pass filter, the combination comprising: a signal generator connected to the power line to which the active band-pass filter is applied, and adapted to produce a plus and a minus reference signal output, and a plus and a minus orthogonal signal output; a reference phase detector connected to receive a signal to be cancelled from the active band-pass filter, and connected to receive a reference signal from said signal generator to produce a reference error signal at the detector output terminal that indicates the magnitude and polarity of the reference component of the signal to be cancelled; an orthogonal phase detector connected to receive the signal to be cancelled and connected to receive an orthogonal signal from the signal generator to produce an orthogonal error signal at the orthogonal phase detector output terminal that indicates the magnitude and polarity of the orthogonal component of the signal to be cancelled; a reference modulator connected to receive said reference error signal and said plus and minus reference signals from the signal generator, and produce a reference feedback signal for said active band-pass filter; and an orthogonal modulator connected to receive said orthogonal error signal and said plus and minus orthogonal signals from the signal generator, and produce an orthogonal feedback signal for the active band-pass filter which is combined with the reference feedback signal and connected to cancel the signal received from the active band-pass filter.

Claim 3

The corrective circuit of claim 1 wherein said phase detectors each have a switching transistor and an integrator circuit.

Claim 4

The corrective circuit of claim 2 wherein the signal to be cancelled is connected to the collectors of said switching transistors and the signal generator outputs connected to the phase detectors are connected to the bases of said switching transistors.

Claim 5

The corrective circuit of claim 1 wherein said reference modulator has two transistors each controlled by said reference error signal, with one transistor connected to receive and amplitude modulate the plus reference signal and the other transistor connected to receive and amplitude modulate the minus reference signal from said signal generator.

Claim 6

The Corrective circuit of claim 4 wherein said orthogonal modulator has two transistors each controlled by said orthogonal error signal, with one transistor connected to receive and amplitude modulate the plus orthogonal signal and the other transistor connected to receive and amplitude modulate the minus orthogonal signal from said signal generator.

Claim 7

An active band-pass filter having an input and output terminal connected together by a power line containing a correction transformer driven by an amplifier, and having a stop-band notch filter with an input connected to the power line, a common point, and an output connected to both the amplifier input and a band-pass filter, wherein the improvement comprises: a signal generator connected to said power line and adapted to produce a plus and a minus reference signal output, and a plus and a minus orthogonal signal output; a reference phase detector connected to both said band-pass filter and a reference signal output of said signal generator, and adapted to produce a reference error signal at its output; an orthogonal phase detector connected to both said band-pass filter and an orthogonal signal output of said signal generator, and adapted to produce an orthogonal error signal at its output; a reference modulator connected to said reference phase detector output and the plus and minus reference signal outputs of said signal generator, and adapted to produce a reference feedback signal at its output; and an orthogonal modulator connected to said orthogonal phase detector output and the plus and minus orthogonal signal outputs of said signal generator, and adapted to produce an orthogonal feedback signal at its output which is combined with said reference feedback signal and fed to the common point of said stop-band notch filter to cancel out power source frequencies tending to appear at the output of said stop-band notch filter.

Claim 8

An active band-pass filter having an input and output terminal connected together by a power line containing a correction transformer driven by an amplifier, and having a stop-band notch filter with an input connected to the power line, a common point, and an output connected to both the amplifier input and a band-pass filter, wherein the improvement comprises: a signal generator connected to said power line and adapted to produce a plus and a minus reference signal output, and a plus and a minus orthogonal signal output; a reference phase detector connected to both said band-pass filter and a reference signal output of said signal generator, and adapted to produce a reference error signal at its output; an orthogonal phase detector connected to both said band-pass filter and an orthogonal signal output of said signal generator, and adapted to produce an orthogonal error signal at its output; a reference modulator connected to said reference phase detector output and the plus and minus reference signal outputs of said signal generator, and adapted to produce a reference feedback signal at its output; and an orthogonal modulator connected to said orthogonal phase detector output and the plus and minus orthogonal signal outputs of said signal generator, and adapted to produce an orthogonal feedback signal at its output which is combined with said reference feedback signal and fed to the common point of said stop-band notch filter to cancel out power source frequencies tending to appear at the output of said stop-band notch filter.

Claim 9

The active band-pass filter as recited in claim 6, wherein said combined reference and orthogonal feedback signals are fed through a phase inverter to the common point on said stop-band notch filter.

Claim 10

The active band-pass filter as recited in claim 6, wherein the reference and orthogonal phase detectors each include: a switching transistor with its collector connected to the band-pass filter and its base connected to receive the signal from the signal generator; and an integrator circuit having an input connected to the collector of the switching transistor and an output producing the error signal.

Claim 11

The active band-pass filter as recited in claim 6, wherein the reference and orthogonal modulators each include: a first transistor having a control element and a controlled element, said first transistor connected to receive the error signal at its control element and amplitude modulate one of the signals from the signal generator connected to its controlled element; a second transistor having a control element and a controlled element, said second transistor connected to receive the error signal at its control element and amplitude modulate the other signal received from the signal generator at its controlled element, such that the two amplitude modulated signals are summed to produce the feedback signal.

Claim 12

The active band-pass filter as recited in claim 6, wherein the signal generator comprises: a keying generator adapted to generate a reference signal to said reference phase detector and an orthogonal signal to said orthogonal phase detector; and a quadrature generator adapted to generate the plus and minus orthogonal signals, and plus and minus reference signals to the modulators with an additional compensation lag.