FAST RECOVERY LOW DISTORTION LIMITER CIRCUIT

A signal limiter for reducing and increasing the gain of a circuit with the required speed of response without introducing distortion in the limiter output. The limiter includes a variable gain circuit having an output coupled to a detector in a feedback loop. The detector develops a DC signal which is then coupled back to the gain control device to reduce or increase the gain in accordance with the output signal level. A charging circuit is coupled to a point between the detector and the gain controlling device to hold a high level signal appearing at the output of the detector for a given time interval. Switching means are then provided to discharge the charging circuit after the lapse of a predetermined time interval to allow the gain to return to normal. This assures that the gain of the gain controlling device will not fluctuate in response to every signal waveform peak. Such rapid fluctuations would result in distortion at the output of the limiter. The switching circuit consists of several forms. One of the forms comprises a transistor having a second charging circuit coupled to the emitter thereof. The discharge time of the second charging circuit allows the transistor to be turned on to discharge the main charging circuit and allow the gain of the gain controlling device to return to normal. In a second form, the second charging circuit is coupled to the base of the transistor, and the operation is similar to that described above. In a further embodiment, a switching means of any general configuration may be provided in shunt with the main charging circuit and operated according to a given timing sequence. In another embodiment, a zener diode may be used to discharge the principal charging circuit when the voltage applied to the anode thereof through a second charging circuit decreases to a given level.