JPH0353819B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an audio channel selection device used, for example, in an SHF receiver.

[Technical background of the invention]

SHF (4 GHz band) broadcasting systems using communication satellites employ a method in which audio signals are FM modulated, and then this FM audio signal is FM modulated and transmitted along with video signals. In this case, F.M.
There are multiple audio signals between 5.0MHz and 8.5MHz,
In other words, there are multiple subcarriers. for example,
In the case of stereo broadcasting, unlike current terrestrial television broadcasting, the stereo signal is not multiplexed onto a fixed subcarrier (4.5MHz), but instead is split between the left (L) channel and right (R) channel.
subcarrier with a different frequency from the channel
FM modulated. Therefore, when receiving such stereo broadcasts, the user needs to tune into each of the L and R channels separately.
Furthermore, another frequency subcarrier includes signals unrelated to the video signal (such as FM broadcasting), and it is also possible to listen to TV audio on the L channel and FM broadcasting on the R channel.

As an audio tuning circuit for this type of SHF transceiver, a system as shown in FIG. 4 has been developed. This system consists of two completely independent frequency synthesizer type tuning circuits.

The received signal frequency-converted by the converter 11 is subjected to gain control by an automatic gain control circuit 12, and then
The signal is input to the FM demodulator 13. The demodulated signal demodulated by the FM demodulator 13 becomes a video signal and a plurality of audio subcarriers. The video signal is extracted by a bandpass filter 14 and guided to an output terminal 15.

Multiple audio subcarriers (5.0MHz to 8.5MHz)
is extracted by bandpass filter 16 and input to mixers 17 and 21. The oscillation output of the local oscillator 31 is also input to the mixer 17, thereby converting a desired subcarrier into an intermediate frequency signal. The intermediate frequency signal output from the mixer 17 is extracted by a bandpass filter 18,
The signal is input to the FM demodulator 19. The demodulated output of this FM demodulator 19 then appears at the output terminal 20. Mixer 21, bandpass filter 22, FM
The demodulator 23 and local oscillator 34 also operate in the same manner.

Here, the local oscillator 31, the prescaler 32,
The first loop formed by the phase-locked loop processing circuit 33 and the second loop formed by the local oscillator 34, prescaler 35, and phase-locked loop processing circuit 36 are independently operated based on tuning data from the microcomputer 37. controlled by. In other words, the local oscillators 31, 34
are voltage-controlled oscillators, and each oscillation frequency can be stably maintained by the function of a phase lock loop.

[Problems with background technology]

The above audio tuning circuit system can obtain an L channel output at the output terminal 20 and an R channel output at the output terminal 24 by adjusting the oscillation frequencies of the local oscillators 31 and 34.

However, this system includes voltage-controlled oscillators 31 and 34 for each channel,
There is a problem in that there is crosstalk between local frequencies and beat disturbance occurs. In other words,
There is no problem if subcarriers with different frequencies are selected for the L channel and R channel, but if the same subcarrier is selected for each channel, there may be a slight deviation in each channel due to variations between the two systems. May be locked at local frequency. Now, the local frequency of the L channel is f ₁ and the local frequency of the R channel is f ₂
Assuming that f1 > f2f. will receive. In such a case, unnecessary carriers are generated as shown in FIG. This can be regarded as the carrier being FM demodulated with the Δf signal, and when FM demodulated, a Δf baseband signal is obtained. In such a case, especially when Δf<15 KHz, a problem arises in that the S/N ratio of the audio signal is significantly degraded.

In order to improve the above problems, efforts have been made to reduce the amount of crosstalk by modifying the ground pattern and devising shielding cases, but the signals that cause crosstalk also affect the resonant circuit of the oscillator. It is thought that the effect is not sufficient. Therefore, when selecting the same subcarrier, lock at a frequency where the local frequency differs by 20KHz or more between channels.
There is an offset on purpose. However, with this method, the intermediate frequency of each channel (10.7M
Hz) signal will also deviate from a predetermined frequency, and if this deviation is large, there is a problem that the audio distortion rate will also increase. Furthermore, if the difference between the intermediate frequencies of each channel is too small, unnecessary carriers are mixed in, resulting in significant deterioration of the S/N ratio.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an audio channel selection device that can reduce beat interference due to crosstalk of local frequency signals between multiple channel systems using a simple method.

[Summary of the Invention] In the present invention, for example, as shown in FIG. 1, the output of the voltage controlled oscillator 41 of one channel is
The above object is achieved by allowing input to the mixer 21 of the other channel via the high frequency switch circuit 49.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention, in which a plurality of audio subcarriers are input to a bandpass filter 16. These multiple audio subcarriers are
This is a signal that is transmitted along with video signals through SHF broadcasting, and exists as an FM signal in the 5.0 to 5.8 MHz band. The output of the bandpass filter 16 is
It is input to mixers 17 and 21. This mixer 1
The stages after 7 and 21 are the same as those explained in FIG. 4, and are given the same reference numerals as in FIG. 4.

Since the present invention is characterized by a local oscillator system, this system will be explained below.

The local oscillation output supply means for the mixer 17 is as follows:
It is composed of a voltage controlled oscillator 41, a prescaler 42, a phase locked loop (PLL) processing circuit 43, and the like. The phase-locked loop processing circuit 43 includes a phase comparison section that performs a phase comparison between the frequency-divided output of the prescaler 42 and the oscillation output of the reference oscillator, a low-pass filter section that converts the output of the phase comparison section into DC, and a prescaler. It includes frequency dividing means for frequency dividing the output of 42. Therefore, the microcomputer 47
When the first selection data DA1 is applied to the frequency division means of the phase-locked loop processing circuit 43 and the frequency division ratio is set, the control voltage VT1 outputted from this phase-locked loop processing circuit 43 is varied and The frequency can be varied.
As a result, the mixer 17 obtains the sum and difference components of the input signal and the local oscillation signal, and for example, the difference component becomes an audio intermediate frequency signal (10.7MHz). The phase-locked loop processing circuit 46 also has the same configuration as the phase-locked loop processing circuit 43 described above, and can control the oscillation frequency of the voltage-controlled oscillator 44 by its output control voltage VT2.
The voltage controlled oscillator 44, prescaler 45, and phase locked loop processing circuit 46 form a phase locked loop.

External data for selecting an audio subcarrier can be input to the microcomputer 47 via a keyboard for each channel. Now, the mixer 17 side is assumed to be an L channel (first channel), and the mixer 21 side is assumed to be an R channel (second channel). If the first and second external data are input to the microcomputer 47 so that the same audio subcarrier is selected for both the L channel and the R channel, the microcomputer 47 inputs the same audio subcarrier based on the first and second external data. and the first and second selection data for each channel.
Generates DA1 and DA2. Then, the first and second selection data DA1 and DA2 are compared, and a determination result is obtained as to whether the difference △f when each data is converted into an oscillation frequency is within a predetermined range (△f<20KHz). be able to.

Now, when the determination result that Δf<20KHz is obtained, the microcomputer 47 operates as a system switching means, and the high frequency switch circuit 49
is set so that the oscillation output of the voltage controlled oscillator 41 is input to the mixer 21 via the buffer circuit 48 and the high frequency switch circuit 49. Also,
At this time, the operation of the other voltage controlled oscillator 44 is stopped by the microcomputer 47.

As a result, when the same audio subcarrier is processed in the L and R channels, the local oscillation output input to the mixers 17 and 21 of each channel is from the single voltage controlled oscillator 41.

When audio subcarriers of different frequencies are processed in each channel, the contents of the first and second selection data DA1 and DA2 are different. Also, at this time, the high frequency switch circuit 49 is switched by the microcomputer 47 so as to input the output of the voltage controlled oscillator 44 to the mixer 21.

Next, the microcomputer 47 can also perform automatic fine-tuning processing. L
I will explain this on behalf of the channel side. In the microcomputer 47, an audio intermediate frequency signal is introduced from the FM demodulation circuit 19 side via a limiter circuit, and its FM detection output is obtained. This FM detection output is then digitally converted, and a shift in the intermediate frequency is detected. If a shift in the intermediate frequency occurs, the first selection data is finely adjusted,
Control is performed to finely adjust the local oscillation frequency in a direction to eliminate the deviation. Similar automatic fine tuning processing can be performed on the R channel side as well.

Next, a processing procedure when channel selection data for selecting an audio subcarrier is input to the microcomputer 47 will be shown and explained.

In FIG. 2, in step S1, first data for channel selection for the R channel is input by the user. The microcomputer 47 selects selected data based on this first data from the outside.
DA1 is input to the phase-locked loop processing circuit 4. This allows you to perform frequency sweeps (steps).
S2) operation is obtained, and a so-called S-shaped detection output is provided from the FM demodulator 19 side to see the fine tuning state. (Step S3). When this S-shaped detection output reaches a predetermined value, the first
The value of selection data DA1 is held and (step
S4) Frequency sweep processing stops. Next, the microcomputer 47 is provided by the user for the L channel. The second external data is read and second selection data is generated in accordance with the second external data. (Step S5). Next, the first selection data for the L channel and this second selection data are compared, and the difference in oscillation frequency determined by each data is determined.
It is determined whether or not it is 20KHz or less (Δf<20KHz). (Steps S6, S7). Here, △f＜20K
Hz, it is determined that the same audio subcarrier should be selected for both the L and R channels, and the high frequency switch circuit 49 switches so that the local oscillation output on the L channel side is introduced into the mixer 21 on the R channel side. (Step S8). 1st above,
If the comparison result of the second selection data is Δf20KHz, an independent phase lock loop is formed for each channel.

The present invention is not limited to the above-mentioned embodiment, but as shown in FIG. may also be made to be able to be led out to the output terminal 24 via the buffer circuit 52. In other words, when external data indicating that the same audio subcarrier is to be selected for the L and R channels is input, the microcomputer 47
stops the voltage controlled oscillator 44, and the analog switch 51 outputs the demodulated output of the L channel to the output terminal 2.
Switch so that it is also derived on the 4th side. Since the other parts are the same as the circuit in FIG. 1, they are given the same numbers as in FIG. 1 and their explanation will be omitted.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to prevent the generation of noise due to crosstalk of local oscillation output signals provided in a plurality of channels. In addition, it is no longer necessary to create a 20KHz deviation in the frequency of the local oscillation signal, which was required in the past, and the characteristics of the bandpass filters 18 and 22, which were required to be relatively strict, are relaxed to some extent, so the design I can afford it.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration of an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the operating procedure of the apparatus shown in FIG. 1, and FIG. 3 is an explanatory diagram of the configuration of another embodiment of the invention. FIG. 4 is a block diagram showing a conventional audio channel selection device, and FIG. 5 is a spectrum explanatory diagram when crosstalk occurs. 17, 21... mixer, 19, 23... FM demodulation circuit, 41, 44... voltage controlled oscillator, 43,
46... Phase locked loop processing circuit, 47...
Microcomputer, 49...high frequency switch circuit, 51...analog switch circuit.

Claims (1)

[Scope of Claims] 1. First and second mixers having in common an input section into which a plurality of audio carrier signals having different frequencies are input; 1,
first and second demodulation means for demodulating a second intermediate frequency signal; first and second voltage control generators for supplying local oscillation outputs to the first and second mixers, respectively; First and second selection data for respectively setting the oscillation output frequencies of the first and second voltage controlled oscillators are input, and each of the voltage controlled oscillators is operated with each control voltage based on these selection data. The difference between the oscillation frequencies of the first and second phase locked loop processing means to be controlled and the first and second voltage controlled oscillators determined by the first and second selection data is within a predetermined range. Determining that the second voltage controlled oscillator is present, and stopping the second voltage controlled oscillator, and demodulating the intermediate frequency signal frequency-converted by the oscillation output of the first voltage controlled oscillator,
An audio channel selection device comprising system switching means for outputting signals to the output terminals of the first and second demodulation means. 2. The system switching means includes a high frequency switch circuit to which the oscillation outputs from the first and second voltage controlled oscillators are input, select one of them, and input it to the second mixer. An audio channel selection device according to claim 1. 3. The system switching means includes an analog switch circuit which receives the outputs of the first and second demodulation means and selects and outputs one of them. Audio channel selection device.