Survival seismic detection system having improved tunable filter

Details Survival seismic detection system having improved tunable filter Survival seismic detection system having improved tunable filter

1991-02-25

1992-07-28

Pihulic, Daniel T.

Communications, electrical: acoustic wave systems and devices

Receiver circuitry

367901, H04B 106

Patent

active

051345919

ABSTRACT:
A survival detection system distinguishes a low frequency survivor generated signal component from ambient low frequency signal components in a seismic sensor signal output. A twin-tee filter circuit a has its input coupled to the sensor signal output and it has a plurality of interconnected charging resistor and capacitor components with an output circuit coupled thereto to generate the detected survivor signal component.
A CMOS switch is connected in each charging current path between the associated resistor and capacitor in such path to control the capacitor charging currents. A bandwidth control circuit applies an adjustable feedback voltage from filter output circuit to the twin-tee filter.
A variable duty cycle generator controls the on-off duty cycle of the CMOS switches to control the effective charging current path resistance and thereby the capacitor charging currents and the tuned or center frequency of the filter. The variable duty cycle generator includes an oscillator having a relatively high frequency output applied to a comparator against a floating variable voltage reference. Variation of the voltage reference produces a comparator output with variable on-off cycling which accordigly operates as a duty cycle control for the CMOS switches and ultimately as filter frequency control.

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