In an AM radio signal receiver, the value of Q of the input tuning circuit is varied in accordance with information indicative of the magnitude of the received signal. This information may be derived from the intermediate frequency (IF) signal processing stage of a superheterodyne receiver. In such a case, the IF signal is applied to a narrow-band filter having a pass band which is narrower than that of the IF signal processing stage. The amplitude of the output signal from the narrow-band filter is then detected to control a variable resistance element which is connected in parallel with winding of an input tuning coil so that the value of Q of the input tuning circuit is lowered when receiving a broadcasting signal having relatively high intensity. The invention may be adapted to an AM stereo receiver. In this case, the variable resistance element is controlled by both a signal indicative of the amplitude of the received signal and a signal indicating that the received signal is a stereo signal.
A bias current source for the output stage of an operational amplifier is controllable. The bias current generator senses the voltage differential on the differential operational amplifier inputs. When an input differential voltage is sensed which generates a rising output signal, additional bias current is provided to the output stage. When the output voltage is constant or falling, the bias current to the output stage is decreased.
In this radio receiver, the charge on a capacitor (14) controls the bandwidth of filters in the receiver's audio circuits. When tuning the radio, a bandwidth control circuit (13) forces this capacitor (14) to discharge, thereby forcing the audio path to be bandwidth restricted, thereby minimizing interstation noise reproduction.
A switching arrangement is provided for coupling a transmitting unit to a transmission line. According to the present invention, a transformer is provided, whose secondary winding is a portion of the transmission line and whose primary winding is connected with the transmitting unit and integrated into a parallel resonance circuit, whose resonant frequency is tuned, each time, to the carrier frequency of the transmitted signal. In addition, a tuning unit may be provided for the automatic tuning of the parallel resonance circuit.
A time signal receiver and decoder receives, detects and stores time information from time signals, e.g., WWV, WWVH, WWVB (USA), JJY (Japan), MSF (UK) and the like. The time information may be used for a self setting clock, and the clock may be used as a reference in time sensitive applications, devices and systems. The time signal receiver may use a high-Q state variable bandpass filter or an anti-notch filter circuit for selectivity at the time signal frequency of interest. The decoder is coupled to the time signal receiver, decodes the time information in the received time signal and may store the decoded time information.
A digital radio receiver generates coherent signals for synchronous detection without use of a phase-locked loop by employing an adaptive notch filter to cancel the desired signal. The cancelling signal is employed as the coherent signal for synchronous detection. The invention obtains faster locking to the desired signal, a wider capture range, and more efficient software coding in a digital signal processing receiver.
