Sanyo Electric Co., Ltd.

Sanyo Semiconductor Co., Ltd.

Keiji Kobayashi

Sakae Sugayama

Yasunari Noguchi

Fumihiro Sasaki

The IFBPF () can variably set a passband width (W) and an attenuation slope (K). The bandwidth control circuit (), which is constituted in hardware, controls the Win accordance with the receiving state, which is composed of a combination of the receiving electric field intensity, the modulation degree, and the intensity of the adjacent-channel interference. A microcomputer () controls the Kon the basis of a program stored in a nonvolatile memory () and finely adjusts the effective passband width. Control of the Wcontradictory for prevention of audio distortion and control of adjacent-channel interference is required when high modulation and adjacent-channel interference exist in a weak electric field state, and the setting becomes difficult. In this particular case, a configuration in which the Kcan be modified by a program allows an advantageous receiving state to be readily obtained.

FM receiver

Adjacent interference is reliably detected in an FM tuner. A receiving field strength judgment circuit () compares a reception field strength signal Sinput from an S-meter circuit () and a reference voltage V, and outputs a receiving strength judgment signal S. An SD band judgment circuit () uses a window comparator to determine, based on an f-V conversion characteristic of a detection output S, whether or not a voltage &#x394;V generated based on Sis within a voltage range corresponding to a narrow band W, and whether or not the voltage &#x394;V is within a voltage range corresponding to a wide band W; and outputs determination signals S, Scorresponding respectively to W, W. An SD circuit () performs a station detection based on Sand S, and determines the presence or absence of adjacent interference based on, e.g., Sand S.

FM tuner having adaptive bandpass filter for adjacent channel interference

An FM tuner that has a multipath reception detection unit and an adjacent-channel interference detection unit while reducing expansion of the scale of the circuit is available. A control signal for a stereo separation level is generated on the basis of a signal Scorresponding to a reception field strength and of a signal Scorresponding to a multipath noise component. The Sis extracted from a fluctuation component signal Sfrom an S-meter circuitby a multipath noise extraction circuitThe multipath noise extraction circuitused for control of the stereo separation level is shared as a portion of the circuitry for detecting the multipath signal reception state. A multipath reception detection unitcompares the Swith a threshold value to detect a multipath reception state.

FM tuner

A variation in tuning frequency of an RF tuning circuit due to temperature changes in a radio receiver is prevented. A tuning frequency of an RF tuning circuit results from a coil (L) and a varicap diode that constitute the RF tuning circuit. A capacitance of the diode is corrected on the basis of a received frequency of a desired station and characteristics of the diode so that the tuning frequency matches the desired station. Thereafter, a temperature is detected by a temperature detection circuit. If a detected temperature T is within 0&deg; C. to 50&deg; C., the tuning frequency of the RF tuning circuit is maintained without change. If the detected temperature T is below 0&deg; C. or higher than 50&deg; C., the tuning frequency is fine adjusted to become lower or higher, respectively.

Radio receiver capable of temperature adjustment to tuning frequency of RF tuning circuit

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. Under the above state, when the electric-field intensity of a received signal reaches a certain level or higher, the frequency control circuit stops the change of frequencies of a local oscillation signal and stops automatic broadcasting-station selection.

Radio receiver having automatic broadcasting-station selecting function

In order to enhance an RF-AGC sensitivity when a station which may cause mutual modulation disturbance is detected, an automatic memory mode is executed so that data on the six stations with first to sixth highest field intensity are preset in a memory. When a receiver intends to receive an object station among the six preset stations, the differences in frequency between the object station and other preset stations are obtained, and whether or not the object station and each of the other stations retain such frequency relationship that may cause mutual modulation disturbance is detected, based on the frequency difference. With an expectation of mutual modulation disturbance, the RF-AGC is set to have higher sensitivity, while, without such expectation, it is set to have lower sensitivity.

Radio receiver with object station sensitivity

A storing circuit for storing control data for a varactor diode, a frequency divided data generating circuit for generating frequency divided data to set the local oscillating frequency of a local oscillating circuit, a determining circuit for computing a receiving frequency from the frequency divided data and determining whether or not the receiving frequency is within a designated frequency range and an arithmetic circuit for executing computation in compliance with data indicating the receiving frequency and control data stored in the storing circuit are provided, and the capacitance of the variable capacitance element is controlled by analog-conversion of an output signal from the arithmetic circuit, thus tracking errors caused by variation in tuning elements are prevented and an RF tuning circuit control interval is reduced.

Radio receiver with programmable digital tuner immune to manufacturing

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. Also, it is possible to set a constant detecting sensitivity by the second level wave-detecting signal against an intermodulation disturbance having a detuning degree over a predetermined value, thereby preventing an excessive sensitivity suppression of the frequency of the desired channel caused by an excessive AGC application.

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Kawanishi, Japan

Keiji Kobayashi