JPS60237713A - Automatic channel selecting device of fm receiver - Google Patents

Abstract

PURPOSE:To perform switching to the passing state of a specified band when the channel selecting device enters a tuning state and tune respective adjacent signals securely by narrowing down the band of a signal inputted to a detuning detecting means forcibly until channel selection data is supplied and the device enters the regular tuning state through automatic fine tuning operation. CONSTITUTION:The output of the high-frequency input part 11 of the automatic channel selecting device is frequency-converted by a frequency converting circuit 12 and a FM signal frequency-converted is inputted to a narrow-band filter 22 or wide-band filter 23 through a switch 21. The FM signal passed through the filter 22 or 23 is demodulated by an FM demodulator 16 and outputted to an output terminal. Further, the S-shaped detection output of the demodulator 15 and a reference voltage are inputted to a comparator 17, which compares both voltages with each other to supplies a logical output corresponding to the shift direction of a tuning frequency to a computer 18. The computer 18 decides on control contents according to the logical output and also controls a PLL circuit 13 to select the filter 22 until the regular tuning state is entered and then switches the filter 22 to the filter 23 once the tuning state is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an automatic tuning device for an FM receiver, and in particular is capable of switching bandpass characteristics from a frequency conversion circuit to an FM demodulator.

[Technical background of the invention]

A conventional FM receiver equipped with an automatic tuning circuit is constructed as shown in FIG. I is a high frequency signal input section, and its output is given to a frequency conversion circuit 12. This frequency conversion circuit 12 includes a phase port and a Frug circuit 13.
A local oscillation output from a voltage-controlled oscillator 14 forming the oscillator is provided. As a result, an FM signal of a constant frequency is obtained from the frequency conversion circuit 12, and this signal is input to the FM demodulator 16 via the bandpass filter 15.

The FM demodulator 16 demodulates the input FM signal and can also derive a so-called S-shaped detection output centered on the FM carrier. The S-shaped detection output is input to the comparator 17. The comparator 17 compares the S-shaped detection output with the reference voltage, and can obtain a logic output according to the direction of deviation of the tuning frequency. This logic output is given to the microcomputer 18, for example. Microcomputer 1
8 determines whether the tuned frequency is shifted upward or downward according to the content of the logic output, and corrects the shift by, for example, a branching section of a branching unit forming a phase shifter and a loop circuit 13ff. Fine tune the ratio. by this,
The output voltage (tuning voltage) of the low-pass filter in the phase-locked Luzo circuit 13 is finely adjusted, and the oscillation frequency is finely adjusted.

Further, if the logic output from the comparator 12 indicates a good tuning state, the automatic fine tuning process by the microcomputer 18 is stopped. The input line 19 is for inputting channel selection data from the keyboard.

[Problems with background technology]

In the conventional automatic channel selection device described above, when audio subcarriers are sent at an interval of 100 kHz, for example, some channels cannot be selected. For example, right now, the broadcast channel is 2.
Assume that the channel interval is 100 kHz. Under this situation, the figure 8 characteristic when the local oscillation frequency fL is swept is as shown in FIG.

Originally, the position of the audio subcarrier Ch2 should have an output characteristic as shown by the broken line, but in reality, the output characteristic is not as shown by the solid line.
It is possible to only detect This is due to the fact that when the spacing between subcarriers is narrow, it is affected by neighboring carriers.

[Purpose of the invention]

This invention was made in order to deal with the above-mentioned circumstances, and is a signal that can be reliably tuned to each channel even if the interval between adjacent subcarriers is narrow, and has a deep modulation degree (approximately 150kHz depiercing). I can also obtain good demodulation.
'The purpose of this invention is to provide an automatic channel selection device for M receivers.

[Summary of the invention]

In this invention, the FM
To achieve the above object, the pass filter for the ll'M signal input to the tuning deviation detection means is forced to be a narrow band filter, and when the normal tuning state is reached, it is automatically switched to the band filter specified by Ude. It is.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows one embodiment of the present invention, in which the output of a high-frequency signal input section 11 is frequency-converted by a frequency conversion circuit 12. The frequency-converted F'M signal is input to either the narrow band filter 22 or the wide band filter 23 via the switch 21, and then reaches the FM demodulator 16. The FM demodulator 16 demodulates the input FM signal and outputs it to an output terminal, and also outputs the center frequency f. 98-character detection output and its reference voltage are output and applied to the comparator 17. In the comparator 17, the S-shaped detection output and the reference voltage are compared,
A logical output can be obtained according to the direction of deviation of the tuning frequency.

This logic output is given to the microcombiner 18, for example. The microcomputer 18 determines whether the tuned frequency is shifted upward or downward depending on the content of the logic output.

For example, phase the mouth to correct that deviation.

The division ratio data of the divider forming the Cruzi circuit 13 is finely adjusted. As a result, 1 phase locked loop circuit 1
The voltage controlled oscillator 140 local oscillation frequency of 3 is subjected to fine adjustment to provide automatic fine tuning.

In the above receiving system, when channel switching is performed, channel selection data (for presetting the division ratio data of the phase lock loop! circuit) is provided via the key gate input line 19. by this,
The local oscillation frequency fL of the voltage controlled oscillator 14 is determined, and the desired channel is received. Then, the state of the S-shaped detection output is monitored and automatic fine tuning processing is performed.

The system of the present invention obtains the basic operation as described above, but in particular, after channel selection is initiated, an automatic fine-tuning operation is performed and the center frequency f is determined from the comparator 17. A special operation is performed until the information that the detection is obtained is obtained. As a result, the present system can obtain reliable tuning for each channel, and will not make channel selection errors as in the conventional system.

The characteristic parts will be explained below. When the channel selection data is input, the microcomputer 18 performs a processing operation to set the local oscillation frequency as described above, but at the same time, it also controls the switch 21 to set the band filter used during the tuning operation period. Forcibly specify. During the tuning operation time, the filter that is forced to be used is the narrowband filter 22. When the microcomputer 18 receives information from the comparator 17 that the center frequency f0 has been detected, the microcomputer 18 returns to the used band filter specified by the user in advance, and completes automatic fine tuning.

According to the present invention described above, the spacing between the Sara carriers is 100
Even if the frequency is as narrow as about kHz, it is possible to obtain the tuning characteristics shown in FIG. 2, and it is possible to accurately tune to each carrier. Figure 2 shows the characteristics when there are two broadcast channels.
The wave detection output is a reference voltage (voltage when the frequency f is output). Tsumashi, channel ch1゜c
In any case where the local oscillation frequency for receiving hJ is set, the S-shaped detection output can serve as the reference voltage. This is because during the tuning process, the narrowband filter 22 is forced to be used, and the carrier input to the FM demodulator 16 is not affected by the adjacent channel carrier.

However, the bandwidth of the narrowband filter 22 at this time is set, for example, to about 75 kHz in the vertical direction around the FM center frequency in order to achieve the above objective. In order to accurately detect the center frequency, a filter with a narrower bandwidth may be used. Therefore, if the modulation degree of the FM modulation signal is deep, the narrowband filter 22 alone may be insufficient for actual audio reception. Therefore, when fine tuning is completed, it is possible to switch to the broadband filter 23 having a wide bandwidth. Further, if the modulation degree is shallow, even if the narrowband filter 22 is continuously used, it may not be enough. Therefore, during reception, the user can specify which filter to use according to his/her preference. This designation is, for example, I h+ −,
j tjfl r 6 <-ffi group 1-yprra+
n+li z Figure 3 shows the data processing process of the microcomputer 18. In step S1, it is determined whether or not channel selection data has been input. If it has been input, data processing for channel selection is performed in step S2. and force the use of the narrowband filter 22. In the next Stella fs3, it is determined whether the information from the comparator 17 indicates normal tuning, and if the tuning frequency is deviated, fine adjustment (automatic fine tuning) is performed in step S4. If proper tuning is obtained, step f85 selects the bandpass filter specified by the user.

FIG. 4 shows a circuit block 6D that executes the flowchart of FIG. 3. The comparator 17 compares the S-shaped detection output AFT with comparison circuits 171, 172, and 113, and the frequency of the input signal is the center frequency f.

Obtain data that shows in which direction the deviation is.

The certain voltage Vl and VJFi values given to the comparison circuits 171, 172.1'13 are different, and as a result, the buffer circuit 174 receives data of either 100.011°001. The reason for setting the reference voltage v1v2 is to provide a dead zone to avoid the influence of noise. In this embodiment, 011 is set as data indicating the tuned state. This data is transmitted to the tuning detection circuit 181
detected by. This tuning detection circuit 181 is 01
When the data of 1 is obtained, the switch 182 can be controlled and the output of the switch 182 can be set to 1.

The switch 182 is also controlled by a channel selection data input detection circuit 183. The channel selection data input detection circuit 183 is
When it is detected that the channel selection data has been input, the switch 18
Set the output of 2 to OK stage. Therefore, the output of the NAND circuit 211 whose one input terminal is given the output of the switch 182 is forced to 1, which controls the switch 212 and forces the narrowband filter 22 to be in use. Next, fine tuning is obtained, and the tuning detection circuit 181
When the output of the switch IFj2 is set to 1, the output of the NAND circuit 21 depends on the output of the user specified data memory 184. If there is a 0 in the memory 184, the output of the NAND circuit 211 will be 1, and the narrowband filter 22 will continue to be used.
Since the output of 1 becomes 0, the wideband filter 23 is used. As a result, the operation shown in the flowchart of FIG. 3 can be obtained.

The present invention is not limited to the above embodiments, and the bandpass filter does not need to be provided independently, and the passband characteristics may be changed by selectively connecting or disconnecting the constituent elements. Furthermore, the number of bandpass filters specified by the user may be further increased, and may be switched depending on the degree of modulation of the signal and the type of signal.

〔Effect of the invention〕

As described above, according to the present invention, an F'M receiver is capable of reliably selecting each channel even when subcarriers are sent at narrow intervals, and can freely handle signals with a deep modulation degree. Automatic channel selection device can be provided.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram showing one embodiment of this invention, FIG. 2 is a diagram showing an example of S-shaped detection output characteristics obtained by this invention, and FIG. 3 is a diagram showing the operating process of the microcomputer shown in FIG. 1. 4 is a diagram showing an example of a circuit that realizes the operation process shown in FIG. 3, FIG. 5 is an explanatory diagram of the configuration of a conventional automatic channel selection device, and FIG. 6 is an S-shaped detection diagram of the device shown in FIG. 5. It is an output characteristic diagram. 18...Microcomputer, 21...Switch, 22...Narrowband filter, 23...Broadband filter. Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (1)

[Claims] Frequency converting means receives a local oscillation output and a high frequency signal and outputs a frequency-converted FM signal; is a voltage value (character 8 detection output), and by being given the tuning information, sets the frequency of the local oscillation output of the local oscillator, and sets the frequency of the local oscillation output of the local oscillator, and also sets the frequency of the local oscillation output from the local oscillator. An automatic tuning device for an FM receiver, comprising means for finely adjusting the frequency of the local oscillation output or stopping the adjustment based on the voltage value information, A plurality of bandpass filters are provided in parallel as a means for guiding the channel to the channel, at least one of which has a narrowband pass characteristic, and when the tuning information is given, the FM signal passes only through the narrowband filter to detect the tuning deviation. If the voltage value information indicates a normal tuning state, the FM signal is introduced into the tuning deviation detection means through the bandpass filter specified by Ude. 1. An automatic channel selection device for an FM receiver, comprising means for setting a filter selection state so as to select a filter.