PROCEDURE AND CIRCUIT FOR FAST DECREASING OF VOLTAGE OF THE DC COMPONENT AND LOW FREQUENCY COMPONENTS AT THE OUTPUT OF THE MIXING CIRCUIT WITHIN THE RECEIVER OF AN UHF RECEIVING-TRANSMITTING UNIT

摘要

A difference between the current of the output current signal (mos) of the mixing circuit (MC) and the current of the controlled current source (CCS) is created which is then transferred to the operation amplifier (A) through a resistor in the return loop. The control voltage (cv) of the controlled current source (CCS) featuring a low-band filter, whose limit frequency is equal to the lower limit frequency of the modulation band within the received signal (rs) represents the filtered voltage at the output of the operational amplifier (A). The procedure is accelerated by first raising the lower frequency of the lower filter at first by two to three levels of magnitude and gradually lowering this frequency to the specified value. According to the invention a very short transient period is achieved at the beginning of reception, so that the operating point with low DC voltage and low-frequency components can be set at least five times faster than with the existing high-band filter.