Circuit for reducing the occurrence of spurious signals on an ou

Details Circuit for reducing the occurrence of spurious signals on an ou Circuit for reducing the occurrence of spurious signals on an ou

1985-11-20

1987-01-13

Mullins, James B.

Amplifiers

Combined with automatic amplifier disabling switch means

330288, 330149, 381 94, H03F 100

Patent

active

046367390

ABSTRACT:
In order to avoid the occurrence of spurious signals on the output (3) of an electrical circuit (1) when the circuit power supply is switched on and off, the output (3) is disconnected from the remainder of the circuit under the control of a control device (5). The control device comprises a current mirror whose input path (T.sub.1, R.sub.1) is in series with a first resistor (R.sub.3) and whose output path (T.sub.2, R.sub.2) is in series with a capacitor (C.sub.1) between the first (10) and the second (20) power supply terminal. The input and the output path are connected to the bases (12, 14) of two transistors (T.sub.3, T.sub.4) which are connected as a differential pair and whose common emitters are coupled to the positive power supply terminal (10) by means of a second resistor (R.sub.4). After switching on of the power supply the capacitor (C.sub.1) is charged via the current mirror (T.sub.1, R.sub.1 ; T.sub.2, R.sub.2 ), so that the differential-pair transistor (T.sub.4) which is coupled to the transistor (C.sub.1) gradually turns off in favor of the other transistor (T.sub.3) of the pair. As a result of this, the output (3) is connected to the electronic circuit (1) some time after switching on of the power supply. When the power supply is switched off the differential-pair transistors (T.sub.3, T.sub.4) are cut off immediately, so that the output (3) is disconnected immediately from the electronic circuit (1).

REFERENCES:
patent: 4315221 (1982-02-01), Numata et al.
patent: 4371841 (1983-02-01), Eckert et al.

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