Abstract: The capacitance value of a variable capacitance element of an RF tuning circuit is controlled in accordance with a control signal Vx. When an automatic search start signal is supplied to a frequency control circuit, frequencies of the local oscillation signal are changed and received frequencies are changed. A storage circuit stores the control data for each predetermined frequency corresponding to the frequency characteristic of the tuning element. When local oscillation frequencies are changed in accordance with an automatic search start signal, an arithmetic circuit computes a control signal Vx in accordance with the data corresponding to the changed received frequency and the control data and thereby, the variable capacitance element is controlled in accordance with the control signal Vx and tuning frequencies are changed so that a tuning frequency coincides with a received frequency.

Abstract: A controller for AGC recognizes a signal level broader than an AGC control output from an AGC circuit and also recognizes a signal level (a desired station signal level) in a narrow-band by an output from an S-meter. No interference, or the occurrence of 2-signal interference or inter modulation interference can be detected from a change ratio of the desired station signal at the time of the alteration of attenuation values of these two signal levels and an RF signal. In consequence, a proper regulation of the RF signal attenuation value can be carried out in accordance with the presence or absence of the interference and the kind of interference, whereby the suitable receive of the signal can always be achieved.

Abstract: An AGC circuit comprising a first level wave-detecting circuit for wave-detecting received signals having been band-limited, having a sensitivity being particularly high for a central frequency of a desired channel and a sensitivity being low for the other frequencies, and a second level wave-detecting circuit for wave-detecting received signals before the band-limitation having a sensitivity being constant irrespective of the frequency. Since the wave-detected signals of these two wave-detecting circuits are mutually added, it is possible to set an optimum detecting sensitivity by the first level wave-detecting signal against adjacent disturbances close to the central frequency of the desired channel, thereby effectively suppressing disturbance signals taking place when the respective intensities of the electric fields of adjacent channels are similar.

Abstract: A cross modulation interference free AM radio receiver with precise channel selection includes an RF amplifying circuit for a radio frequency (RF) signal incoming through an antenna (1; 101) to output a wide band RF signal and an automatic gain control (AGC) circuit (7; 107) for controlling the gain of the RF amplifying circuit in accordance with the field strength of the wide band RF signal. A circuit (3, 4, 5, 6; 109, 110, 111, 112, 113) as provided for extracting a desired signal from the wide band RF signal, and a first control circuit (81; 114, 116, 118) for reducing the AGC effect of the AGC circuit in a decrease in the field strength of the desired signal which results in an increase in the amplification rate of the RF amplifying circuit. A second control circuit (8) makes the first control circuit non-operative in response to an instruction of an automatic channel selection at which time the AGC circuit performs an AGC operation only in accordance with the field strength of a wide band RF signal.

Abstract: A FM receiver quickly suppressing defective effect of multipath reflection interference is disclosed. A field strength detecting circuit (8) is responsive to output signals from preceding stage amplifiers (51) in an IF amplifying circuit (5) for detecting the field strength of the received signal. In response to the field strength detecting circuit (8), a soft muting control circuit (10) is operated, whereby a muting circuit (7) gradually mutes the output signal of a detector circuit (6). Furthermore, an alternate current signal detecting circuit (12) detects the alternate current signal component included in the output signal from the field strength detecting circuit (8), whereby the occurrence of multipath reflection interference is detected.

Abstract: An AM radio receiver includes an automatic tuning circuit for setting an automatic tuning mode. A radio frequency circuit produces a tuned signal and an untuned signal. A selector receives the tuned signal and untuned signal, and selects the tuned signal when the automatic tuning mode is set, and selects the untuned signal when the automatic tuning mode is not set. An intermediate frequency signal generator produces an intermediate frequency signal based on the selected signal.

Abstract: A semiconductor integrated circuit is formed on a semiconductor chip (1) and it includes: a plurality of mat regions (A to T) each including a plurality of circuit elements (10 to 13); partition regions (4) for spacing the mat regions (A to T) from each other; and a pair of power supply line (2) and ground line (3) disposed on each of the partition regions (4). An electronic circuit formed on the semiconductor chip (1) includes circuit blocks having different functions but it is designed for a unit of each mat (A to T) not for a unit of each circuit block.

Abstract: A semiconductor integrated circuit for a radio comprises: a front end circuit block (1) including at least an oscillation circuit (1b) and a mixing circuit (1c), for converting an RF signal to an IF signal; and an IF amplifying circuit block (2) for amplifying the IF signal and limiting an amplitude thereof, and the front end circuit block (1) is covered with shield electrodes (17, 17a, 17b, 17c) connected to a predetermined potential.

Abstract: A semiconductor integrated circuit for a radio comprises: a front end circuit block (1) including at least an oscillation circuit (1b) and a mixing circuit (1c), for converting an RF signal to an IF signal; and an IF amplifying circuit block (2) for amplifying the IF signal and limiting an amplitude thereof, and the front end circuit block (1) is covered with shield electrodes (17, 17a, 17b, 17c) connected to a predetermined potential.

Abstract: The disclosure relates to an automatic search tuner in which an erroneous stop of an automatic search operation can be prevented by an interference signal generated due to an intermodulation interference. The automatic search tuner comprises an attenuating means for attenuating the level of a received signal in a predetermined amount in response to a signal indicative of stopping an automatic search operation; and a comparing means for comparing the level of a signal obtained when the attenuating means is operating with the level of a signal obtained when the attenuating means is not operating. An automatic search operation is resumed by the signal outputted from the comparing means.

Abstract: The disclosure relates to a radio which prevents the level of a signal transmitted from a desired broadcasting station from being suppressed by the operation of a broad band automatic gain control circuit in the presence of an interference signal. The radio comprises a first detector for detecting the intensity of the electric field of a received signal; a second detector for detecting whether or not the broad band automatic gain control is operating; and a device for changing the tuning condition of a radio frequency tuning circuit in a small extend in response to the signals outputted from the first and second detectors.