Filter having an automatically controlled variable cut-off frequ

Details Filter having an automatically controlled variable cut-off frequ Filter having an automatically controlled variable cut-off frequ

1976-01-14

1977-08-30

Rolinec, Rudolph V.

Electricity: measuring and testing

Measuring, testing, or sensing electricity, per se

Frequency of cyclic current or voltage

324 77E, 328167, 330129, 330109, 330149, G01R 2302

Patent

active

040457311

ABSTRACT:
A device for measuring the frequency or period of an input signal independent of different frequency noise signals which may be superimposed on the input signal includes a filter circuit having a variable cut-off frequency. The output level of the filter circuit is detected by a level detector, the output of which electrically controls a variable element such as a variable resistor, a variable capacitance diode or the like which is included in the filter circuit. This controls the cut-off frequency of the filter circuit, so as to maintain its output level at a given level. In this manner, an input signal frequency is converted into a corresponding level, utilizing a declining portion adjacent to the cut-off frequency of the frequency response of the filter circuit. The converted level is utilized to vary the cut-off frequency of the filter circuit to maintain its output level constant, thereby automatically changing the cut-off frequency in accordance with the input signal frequency.

REFERENCES:
patent: 3297882 (1967-01-01), Broadhead, Jr.
patent: 3665345 (1972-05-01), Dolby
patent: 3729693 (1973-04-01), Dolby
patent: 3839673 (1974-10-01), Acker
patent: 3904975 (1975-09-01), Satoh

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