Tunable active high-pass filter

Details Tunable active high-pass filter Tunable active high-pass filter

1980-06-26

1982-04-20

Mullins, James B.

Amplifiers

With semiconductor amplifying device

Including signal feedback means

330306, H03F 138

Patent

active

043261728

ABSTRACT:
A tunable active high-pass filter particularly for use in hearing aids, which comprises merely a transistor as the active amplifying element. Three series-connected capacitors are connected between the input of the filter and the base of the transistor. A first resistor branches off from the junction between the first and second capacitors, a second resistor branches off from the junction between the second and third capacitors, and both resistors are connected, via a third resistor which is adjustable, to the emitter of the transistor which constitutes the output of the filter. A further resistor extends from the junction between the third capacitor and the transistor base to the source of operating potential which, for example, is positive. Preferably, each of the capacitors forms a high-pass filter with its respectively connected resistor with the first and second resistors, i.e. the resistors of the first and second high-pass filters, being located in the positive feedback path between the emitter of the transistor and its base. By the adjustment of only the value of the adjustable resistor, the steepness or slope of the filter can be varied within wide limits.

REFERENCES:
patent: 3525949 (1970-08-01), Fjallbrant
Buttkus, "Abgleichbare Aktive Filter und ihe Berechnung", Funkschau, 1978, Issue 5, pp. 183, 184.

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