JPS639153Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to a digital tuning device.

A phase-locked loop (hereinafter abbreviated as PLL) is generally used in the digital tuner part of AM and FM broadcast wave band receivers and communication receivers, and the PLL performs digital processing and automatically selects signals. When broadcast, this tuning device is called a digital tuning device.

The role of the PLL circuit is to create an accurate predetermined frequency, so that the frequency mixer converts the high frequency of the high frequency amplifier circuit into the required accurate intermediate frequency (for example, 10.7 MHz for an FM broadcast band receiver).
etc.). The frequency generated by the PLL circuit, that is, the frequency of the local oscillation circuit, is determined by comparing the frequency output by the local oscillation circuit divided by 1/n with the phase of the reference frequency of the crystal oscillator, and calculating the frequency according to this phase difference. The voltage is applied to the varactor diode, which is a variable capacitance diode in the tuning circuit of the local oscillator circuit, to adjust the tuning.
It is accurate as long as the reference frequency of the crystal oscillator does not change. On the other hand, the antenna circuit also has a tuning circuit in order to properly receive the signal of the reception channel.
The high frequency amplifier circuit also has a tuning circuit to properly amplify the output signal of the antenna circuit. Conventionally, the tuning circuits of antenna circuits and high-frequency amplifier circuits are controlled by converting the error pulse output from the phase comparator of the PLL circuit into DC using a low-pass filter, and applying this to the varactor of each tuning circuit. It was something that would be done.

That is, it is assumed that if the tuning circuit of the local oscillation circuit on the PLL circuit side is tuned, the antenna circuit and the high-frequency amplification circuit will be tuned in the same way. However, the characteristics of each tuning circuit are generally different from each other, and therefore, even if the tuning circuit of the local oscillation circuit is accurately tuned, the tuning of the antenna circuit and high frequency amplifier circuit is not necessarily appropriate.

The present invention has been made in order to eliminate such drawbacks, and it is an object of the present invention to provide a digital tuning device having a frequency tuning device that adjusts the tuning of an antenna circuit and a high frequency amplifier circuit in accordance with the output signal value of an intermediate frequency amplifier. With the goal.

The present invention will be explained below with reference to the drawings.
FIG. 1 is a block diagram of a digital tuning device having a tuning adjustment device according to an embodiment of the present invention. 1 is an antenna, 2 is an attenuator that attenuates the received signal to an appropriate level, 3 is a tuning circuit for the antenna circuit, 4 is a high frequency amplification circuit, and 5 is a high frequency amplification circuit 4
, 6 is a frequency mixer, 7 is an intermediate frequency amplifier, 8 is a signal level amplifier, 9 is a signal level indicator, 10 is an FM detector, 11 is a multiplex (hereinafter abbreviated as MPX) demodulator, 12 is a muting circuit. The PLL circuit includes a local oscillation circuit 13 and a tuning circuit 1 of the voltage controlled local oscillation circuit 13.
9, programmable frequency divider 14, reference oscillation circuit 1
5, a crystal resonator 16, a phase comparator 17, and a first low-pass filter 18.
20 is a second low-pass filter whose output is connected to the tuning circuit 5, and whose input is connected to the output of the phase comparator 17 or the output of the first pulse width modulator 24 by the first switch circuit 21. Selectively connected. Further, 22 is a third low-pass filter whose output is connected to the tuning circuit 3, and whose input is connected to the phase comparator 1 by a second switch circuit 23.
7 or the output of the second pulse width modulator 25. 26 is a control circuit that detects the level value of the output signal of the intermediate frequency amplifier 7 and modulates the pulse widths of the pulse width modulators 22 and 25 by outputting a control signal so that this level value becomes maximum. and the switch circuits 21 and 2
3 is appropriately switched and controlled. 27 is a switch panel having a tuning switch and a power switch, 28 is a frequency display circuit, and 29 is a memory circuit.

Next, the operation of the embodiment will be explained with reference to the drawings. When the power switch and tuning switch of the switch panel 27 are turned on, the entire tuning device is put into operation. Next, when a desired tuning button is pressed using the tuning switch, the control circuit 26 stores data corresponding to the tuning in advance into the memory 2.
9, the selected frequency is displayed on the display circuit 28 via the control circuit 26. The signal is then input to the programmable frequency divider 14, whereby a desired frequency is obtained in the local oscillation circuit 13 of the PLL circuit. At this time, since the operation of the PLL circuit is locked, a voltage suitable for tuning is applied to the varactor of the tuning circuit 19. Similarly, the tuning circuits 3 and 5 also include low-pass filters 20 and 2.
A corresponding voltage is applied via 2. This case will be referred to as initial setting of tuning. After the initial setting is completed, the switch circuits 21 and 23 are controlled by the control circuit 26, and the low-pass filter 20 and the pulse width modulator 24 and the low-pass filter 22 and the pulse width modulator 25 are connected. Here, the intermediate frequency signal obtained by inputting the tuning frequency output from the tuning circuit 5 and the local oscillation frequency output from the local oscillation circuit 13 to the frequency mixer 6 is input to the intermediate frequency amplifier 7. be done. The control circuit 26 controls the pulse width modulators 24 and 25 while detecting the output signal level of the intermediate frequency amplifier 7, and modulates the pulse width so that the output signal level of the intermediate frequency amplifier 7 is maximized. The intermediate frequency signal for which the tuning operation has been completed is output from the intermediate frequency amplifier 7, passes through the signal level amplifier 8, and the magnitude of its level is displayed on the signal level display 9.
It is also demodulated into an audio signal by the FM detector 10,
Furthermore, it is demodulated into stereo signals for R and L channels by an MPX demodulator. In this state, the muting release control signal is input from the intermediate frequency amplifier 7 and the FM detector 10 to the muting circuit 12, so the stereo signals for the R and L channels are output as the output of the digital tuning device. . In areas with strong electric fields, it is easier to set the maximum point by weakening the high frequency input signal to the tuning circuit 3 of the antenna circuit by a predetermined amount, so the attenuator 2 is controlled to set the high frequency input signal at an appropriate level.

As explained above, according to the present invention, the antenna circuit and the high frequency amplification circuit can be tuned independently, so that optimal tuning can be obtained.

In the embodiment, the switch circuits 21 and 23 are automatically switched by the control circuit 26, but a configuration in which the switch circuits 21 and 23 are switched manually via the switch panel 27 is also possible. A combination of automatic and manual operation is also possible. Although the embodiment has been described using a tuning device for the FM broadcast wave band, it is also applicable to the case of the AM broadcast wave band.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a digital tuning device according to an embodiment of the present invention. 1...Antenna, 2...Attenuator, 3.5.19
... Tuning circuit, 4 ... High frequency amplifier circuit, 6 ... Frequency mixer, 7 ... Intermediate frequency amplifier, 13 ... Voltage control local oscillation circuit, 14 ... Programmable frequency divider, 15 ... Reference oscillator, 16 ... Crystal resonator, 17 ... Phase comparator, 18 ... First low-pass filter, 20 ... Second low-pass filter,
22...Third low-pass filter, 21...First
switch circuit, 23... second switch circuit,
24...first pulse width modulator, 25...second pulse width modulator, 26...control circuit, 27...switch panel, 29...memory circuit.

Claims (1)

[Claims for Utility Model Registration] A crystal oscillator, a reference oscillation circuit, a phase comparator, a first low-pass filter, a voltage that converts the selected frequency input from the antenna into an intermediate frequency using a frequency mixer. A second low-pass filter which inputs the output signal of the phase comparator and converts it into a DC signal; an antenna circuit including a tuning circuit that responds to the frequency tuning of a received signal from the antenna; a third low-pass filter that receives the output signal of the phase comparator and converts it into a DC signal; and a third low-pass filter that responds to the DC signal. A digital tuning device having a frequency tuning device including a high frequency amplifier circuit including a tuning circuit that performs frequency tuning of an output signal of the antenna circuit, a first pulse width modulator, and a second pulse width modulator. a width modulator; and a first switch, one end of which is connected to the input terminal of the second low-pass filter, and the other end of which can be selectively connected to the output of the first pulse width modulator or the output of the phase comparator. a second switch circuit, one end of which is connected to the input terminal of the third low-pass filter, and the other end of which can be switched between the output of the second pulse width modulator or the output of the phase comparator; The first switch circuit is switched and controlled to connect the first pulse width modulator and the second low-pass filter, and the second switch circuit is switched and controlled to connect the first pulse width modulator and the second low-pass filter. vessel and said third
A frequency tuning device comprising: a low-pass filter connected to the intermediate frequency amplifier; and a control device that detects the output signal value of the intermediate frequency amplifier and modulates and controls the output pulse width of the pulse width modulator so that the signal value becomes maximum. A digital tuning device with