Sanyo Electric Co., Ltd.

Hisao Ishii

Sakae Sugayama

Shinichi Yamasaki

Shinichi Yamazaki

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. A third control circuit (118) sets the AGC circuit in forced AGC state where the gain of the RF amplifying circuit is minimized when the field strength of the desired signal is above a first reference value, and a sensitivity switching circuit (119) reduces the sensitivity of the AGC circuit to the wide band RF signal field strength when the field strength of the desired signal is below a second reference value.

Radio receiver comprising automatic gain controlling function

An RF signal received by an antenna is amplified in an amplifier circuit and is then tuned in a tuned circuit to pick up a signal having a certain frequency and a certain level. Then, the picked up signal is mixed with another signal to output an IF signal and the IF signal is detected to reproduce the desired broadcasting program. An AGC circuit ensures high and low levels of the received signal to make the received signal to a certain level. Further, a damping circuit capable of switching a damping amount by a sensitivity switching signal is arranged in the rear stage of the AGC circuit. Hence, intensity of a signal for performing a detection or the like can be exactly switched based of the sensitivity switching signal in an automatic broadcasting station selection.

Sensitivity switching circuit for radio receiver

In a signal-strength-peak detecting circuit, tuning frequencies by a tuning circuit are periodically varied. Wide band seek is performed according to a signal level of the varied frequencies. When the signal level is greater than a predetermined value, a fine tuning circuit varies tuning frequencies to perform narrow band seek. Further, change of signal levels is detected during narrow band seek to decide whether the peak of the signal level is trapezoidal or rounded. When the peak is decided to be rounded, the maximum value is used as the peak. On the other hand, when the peak is decided to be trapezoidal, the central point of an upper side of the trapezoid is selected as an optimum peak.

Signal-strength-peak detecting circuit for automatic tuning circuit

A radio receiver responsive to a received RF signal containing a plurality of channel frequencies each having broadcast information which includes a circuit for producing a wide band version of the received RF signal and a circuit for producing a narrow band version of the received RF signal. Selection of a channel at a given frequency is accomplished by using the wide band version of the received RF signal and after such selection is made, the narrow band version of the signal is used for further reception of the selected channel frequency and reproduction of the information thereon.

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Ashikaga, Japan

Hisao Ishii