JPH0133049B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an improvement in a radio receiver that performs electronic tuning using a semiconductor variable capacitance element.

(b) Background of the Technology So-called electronically tuned radio receivers that use semiconductor variable capacitance elements as tuning elements and perform reception tuning by controlling the capacitance of the semiconductor variable capacitance elements by increasing and decreasing the applied voltage have already been put into practical use. There is.
The electronically tuned radio receiver is mechanically stronger and has better electrical characteristics than the conventional mechanical radio receiver that uses a variable capacitor, and the front end can be made more compact, and it is also capable of manual tuning and auto tuning. It has many advantages such as easy tuning and preset tuning functions and convenient tuning operations.
However, electronically tuned radio receivers have the disadvantage that tracking errors occur due to variations in the capacitance change characteristics of the semiconductor variable capacitance elements, or changes in the capacitance change characteristics due to the magnitude of the superimposed oscillation voltage. This tracking error is particularly noticeable in AM receivers where the reception band ratio is large, and performance is often not uniform across the entire reception band. Currently, these problems can be covered to some extent by selecting semiconductor variable capacitors and improving circuit technology, but they are not perfect. For this reason, tracking adjustment is performed during the production process, but tracking adjustment is troublesome and is prone to adjustment errors.

(C) Means for Solving the Problems The present invention eliminates the above-mentioned drawbacks and provides a radio receiver that has no tracking errors without selecting semiconductor variable capacitance elements or making tracking adjustments. It is.

(D) Embodiment The present invention will be explained below with reference to the drawings. 1 is an antenna, and 2 is a high frequency amplification circuit connected to the antenna 1, for tuning to the frequency of a broadcast signal received by the antenna 1. It has a tuning circuit consisting of a semiconductor variable capacitance element and a coil. 3 is a mixing circuit that mixes the high frequency signal from the high frequency amplifier circuit 2 and the local oscillation signal from the local oscillation circuit 4 whose oscillation frequency is controlled by a semiconductor variable capacitance element to generate an intermediate frequency signal; 5 is the mixing circuit that generates an intermediate frequency signal; An intermediate frequency amplification circuit that amplifies the intermediate frequency signal from the mixing circuit 3, 6 is a detection circuit, and the detected audio signal is applied to the audio amplification circuit 7 and amplified, and then sent to the speaker 8.
to drive. Reference numeral 10 denotes a tuning volume for obtaining a tuning voltage supplied to each of the semiconductor variable capacitance elements from a tuning power supply 11, and a portion of the tuning voltage is directly applied to the local oscillation circuit 4. Reference numeral 12 denotes a DC voltage control circuit for correcting and applying the tuning voltage supplied from the tuning volume 10 to the semiconductor variable capacitance element of the high frequency amplifier circuit 2, and is controlled by a detection signal from the peak value detection circuit 13. . As shown in FIG. 2, the DC voltage control circuit 12 includes an RS flip-flop 14 and an RS flip-flop 1.
a control circuit 15 that is inoperable at 4;
An oscillation circuit 16 controlled by the control circuit 15, and a clock pulse generation circuit 1 that converts the oscillation signal from the oscillation circuit 16 into a clock pulse signal.
7. Up-down counter 1 that counts the clock pulse signal and generates a 5-bit output pulse.
8. It consists of an output circuit 19 that converts the 5-bit output pulse into an analog signal, a light emitting diode 20 connected to the output circuit 19, and a light receiving element 21 optically coupled to the light emitting diode 20.

Next, the operation of the radio receiver of the present invention will be explained. First, to select a channel, the tuning volume 10 is operated. Then tuning power supply 1
The tuning voltage obtained from 1 is increased or decreased. A part of the tuning voltage is directly supplied to the semiconductor variable capacitance element of the local oscillation circuit 4 to change the capacitance of the semiconductor variable capacitance element. The tuning voltage is also applied to the semiconductor variable capacitance element of the high frequency amplifier circuit 2 via the DC voltage control circuit 12 to change the tuning frequency of the tuning circuit of the high frequency amplifier circuit 2. As the tuning frequency of the tuning circuit is changed, it is tuned to the frequency of one broadcast signal received by the antenna 1. Therefore, the broadcast signal is applied to the high frequency amplifier circuit 2 and amplified, then applied to the mixing circuit 3 and mixed with the local oscillation signal of the local oscillation circuit 4. At this time, if the tuning volume 10 is operated as described above so that the difference between the oscillation frequency of the local oscillation signal and the frequency of the broadcast signal being received is exactly the intermediate frequency, the intermediate frequency will be output from the mixing circuit 3. I get a signal. By the way, when tuning is performed by operating the tuning volume 10 to change the capacitance of the semiconductor variable capacitance element, the difference between the oscillation frequency of the local oscillation signal and the frequency of the broadcast signal may occur due to variations in the semiconductor variable capacitance element. Even if the local oscillator circuit 4 is controlled to exactly match the intermediate frequency, the tuning frequency of the tuning circuit of the high frequency amplifier circuit 2 may not always match the frequency of the broadcast signal being received. Therefore, the present invention operates the tuning volume 10 to tune the oscillation frequency of the local oscillation circuit 4 to accurately match the difference between the frequency of the broadcast signal and the intermediate frequency. When the frequency is not tuned to the frequency of the broadcast signal being received, the DC voltage control circuit 12 corrects the tuning voltage applied to the semiconductor variable capacitance element of the high frequency amplifier circuit 2 so that the tuning frequency of the tuning circuit becomes the receiving frequency. so that it is equal to That is, when tuning starts, RS flip-flop 1
4 is set and the control circuit 15 is operated. Then, the oscillation circuit 16 oscillates and generates a signal. The signal is converted into a clock signal by a clock signal generation circuit 17, and is applied to an up-down counter 18 via a control circuit 15, where the up-down counter 18 counts. The count output of the up-down counter 18 is output to the output circuit 1.
At step 9, the signal is converted into an analog signal having a magnitude corresponding to the count number, and is applied to the light emitting diode 20. Therefore, as the up-down counter 18 counts, the luminance of the light emitting diode 20 gradually increases, so that the resistance value of the light receiving element 21 decreases. Since the semiconductor variable capacitance element of the high frequency amplifier circuit 2 is set in advance to a voltage smaller than the optimum value by the resistors 22 and 23, the tuning volume 10 is lowered as the resistance value of the light receiving element 21 decreases. The tuning voltage increases, changing the capacitance value of the semiconductor variable capacitance element and bringing the tuning frequency of the tuning circuit closer to the frequency of the broadcast signal being received. When the tuning frequency of the tuning circuit approaches the frequency of the broadcast signal, the intermediate frequency signal from the intermediate frequency amplifier circuit 5 becomes larger. When the tuning frequency of the tuning circuit of the high frequency amplifier circuit 2 is completely tuned to the reception frequency, the intermediate frequency signal becomes maximum. This is detected by the peak value detection circuit 13, and the peak value detection circuit 13 generates a pulse signal. The pulse signal is applied to the reset terminal of RS flip-flop 14 to reset RS flip-flop 14. Then, the control circuit 15 is rendered inactive and stops supplying clock pulses to the up-down counter 18, so the up-down counter 18 stops counting and the output circuit 1
The magnitude of the signal of 9 is maintained at that state. Therefore, the tuning voltage supplied to the high frequency amplifier circuit 2 becomes constant and the tuned circuit is held at its tuned frequency.

Therefore, one broadcast signal received by the antenna 1 passes through the high frequency circuit 2 without loss, is mixed with the local oscillation signal of the local oscillation circuit 4 in the mixing circuit 3, is converted into an intermediate frequency signal, and is amplified in the intermediate frequency amplifier circuit 5. After that, the signal is detected by a detection circuit 6 and converted into an audio signal. The audio signal is amplified by an audio amplification circuit 7 and drives a speaker 8. In the above description, in accordance with the count output of the up-down counter 18, the light emitting diode is caused to emit light by the analog signal obtained from the output circuit 19, and the resistance value of the light emitting diode optically coupled to the light emitting diode is changed. The tuning voltage supplied to the semiconductor variable capacitance element is set to an optimum value, but a transistor is connected instead of the light emitting diode, and the impedance between the emitter and collector of the transistor is changed by the signal from the output circuit 19, The tuning voltage supplied to the semiconductor variable capacitance element may be adjusted to an optimum value.

(E) Effect As described above, in the radio receiver of the present invention, in which tuning is performed by applying a tuning voltage to each semiconductor variable capacitance element of the high frequency amplifier circuit and the local oscillation circuit, first, the frequency of the local oscillation signal of the local oscillation circuit is The difference between the receiving frequency of one broadcast signal and the received frequency is made to be exactly the intermediate frequency, and then the tuning voltage applied to the semiconductor variable capacitance element of the high frequency amplifier circuit is corrected using the signal generated from the up/down counter of the DC voltage control circuit. However, since the tuning circuit is completely tuned to the frequency of the broadcast signal to be received, even if there are variations in the semiconductor variable capacitance elements, the signal can always be received in a good condition without tracking adjustment.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a radio receiver of the present invention;
FIG. 2 is a circuit diagram showing the main part of the present invention. 2...High frequency amplification circuit, 3...Mixing circuit, 4...
... Local oscillation circuit, 5 ... Intermediate frequency amplification circuit, 10
... Tuning volume, 12 ... DC voltage control circuit, 13 ... Peak value detection circuit.

Claims (1)

[Claims] 1. A high-frequency amplification circuit whose tuning frequency can be changed by changing the capacitance of a semiconductor variable capacitance element, a mixing circuit connected to the high-frequency amplification circuit, and a semiconductor variable capacitor that controls the oscillation frequency of a local oscillation signal supplied to the mixing circuit. a local oscillation circuit having an element, an intermediate frequency amplification circuit that amplifies an intermediate frequency signal obtained from the mixing circuit, and a tuning voltage generation circuit that supplies a tuning voltage to each semiconductor variable capacitance element of the high frequency amplification circuit and the local oscillation circuit. and a peak value detection circuit that detects the peak value of the intermediate frequency signal, a control circuit controlled by the output of the peak value detection circuit, and a signal that is counted up or down by the control circuit and added to the high frequency amplification circuit. and a DC voltage control circuit consisting of an up-down counter that corrects the tuning voltage generated by the tuning voltage, and the tuning voltage from the tuning voltage generating circuit accurately adjusts the frequency difference between the oscillation frequency of the local oscillation circuit and the broadcast signal received at that time. Select the station to reach the specified intermediate frequency,
Thereafter, the tuning voltage supplied to the high-frequency amplifier circuit is decreased or increased by the signal generated by the up-down counter, and the tuning circuit of the high-frequency amplifier circuit is made to match the frequency of the received broadcast signal, and at this time, the peak value is detected. A radio receiver characterized in that a control circuit is rendered inoperable by the output obtained from the circuit.