JPH024543Y2 - - Google Patents

Description

[Detailed description of the invention] Technical field This invention is a TV and FM system that can selectively receive either television broadcasting or FM broadcasting.
Regarding broadcast receivers.

BACKGROUND TECHNOLOGY The carrier waves of FM broadcasting, which have recently been put into practical use, occupy the 76MHz to 90MHz band as shown in Figure 1, and the carrier waves of television broadcasting occupy the upper 90MHz to 90MHz band.
It is located in the 108MHz band. As is well known, the audio signal of television broadcasting is composed of FM modulated waves similar to FM broadcasting. In recent years, focusing on this point, television broadcast receivers have been put into practical use that incorporate a front end such as an FM tuner so that they can also receive FM broadcasts. Here, even if the audio signals of both broadcasts use the same FM modulation method, the maximum frequency deviation is ±25K in the case of television broadcasting, as shown in Figure 2.
Hz, differs from ±75KHz in the case of FM broadcasting. Therefore, the audio signals of both broadcasts are converted to FM using a common demodulator.
When demodulated, since the demodulator has an S-curve as shown in FIG. 3, as is well known, the difference in the maximum frequency deviation, or in other words, the modulation degree, appears as a difference in the demodulated output level. That is,
In FIG. 3, the intermediate frequency output A1 of the television broadcast appears as A2 after demodulation, and the intermediate frequency output B1 of the FM broadcast appears as B2. As a result, the audio output level differs each time the receiver switches to selectively receive one of the two broadcasts. Conventionally, this required the viewer to manually adjust the level each time, but this was extremely troublesome.

DISCLOSURE OF THE INVENTION This proposal has been made in view of these points, and its purpose is to provide a shared demodulator for TV and
In TVs and FM broadcast receivers that demodulate FM broadcast audio signals, the system automatically corrects the demodulated audio output level so that there is no difference when switching between TV and FM broadcast reception.

Therefore, the feature of the structure of this case is TV broadcasting.
When determining whether it is an FM broadcast, a predetermined point in the reception output of a predetermined TV or FM broadcast, such as tuning voltage, reception carrier frequency, local oscillation frequency, etc., is determined in advance, and the received signal is larger than this point. A discriminator is provided that generates a discrimination output for the broadcast by checking whether the broadcast is small or small, and the input signal level to the amplifier disposed after the FM demodulator is determined in advance according to this discrimination output. The point is that a gain adjuster is provided to control the gain to a constant level.

As a result, according to this proposal, it is possible to make maximum use of each circuit section already provided in the receiver, and to minimize the number of new circuits that need to be added, thereby eliminating the complication of conventional viewers. operation can be eliminated.

BEST MODE FOR CARRYING OUT THE INVENTION Fig. 4 is a block diagram showing the schematic configuration of a conventional TV and FM broadcast receiver of this type. It is a comparison of what is possible. In Fig. 4, reference numeral 1 indicates a key switch operated by the viewer to issue a channel selection command, a volume increase/lower command, a TV or FM broadcast selection switching command, a power on/off control command, etc. This is a key operation section including an encoder that outputs a pulse signal of a predetermined code corresponding to each, for example, a code composed of 6 bits as shown in FIG. 2 is a decoder section which receives this pulse signal and decodes the above code. 3 is a well-known FM tuner for receiving FM broadcasts, 4 is a local oscillator for FM broadcasts,
5 is a well-known 10.7MHz intermediate frequency amplifier, 6 is FM
Demodulator, 7 is a volume adjustment circuit, 8 is a low frequency amplifier,
Reference numeral 9 denotes a speaker, which is equivalent to a well-known FM receiver. On the other hand, 10 is VHF,
TV tuner capable of UHF reception, 11 is a video intermediate frequency amplifier, 12 is a video detector, 13 is a video amplifier, 14 is a high frequency AGC circuit, 15 is an AFT detection circuit, 16 is a video output amplifier, 17 is a horizontal and vertical deflection circuit and a deflection circuit including horizontal and vertical synchronizing signal separation circuits, and 18 a cathode ray tube, which is constructed from a structure equivalent to a well-known television receiver. Here, 19 is a second local oscillator which outputs a local oscillation frequency of 100.7MHz to 118.7MHz as shown in FIG. Further, 20 is a second mixer, which mixes the audio intermediate frequency of the TV broadcast output from the TV tuner 10.
Convert to 10.7MHz intermediate frequency in FM broadcast receiver. Therefore, in a well-known television receiver, the above-mentioned FM broadcast receiving system and this second
Local oscillator 19 and second mixer 20 are not provided.

The FM tuner 3 and local oscillator 4 shown in FIG. 4 are actually constituted by a circuit as shown in FIG. 6. In this circuit, the antenna is connected to the terminal 41, and the antenna is connected to the terminal 41 from the decoder section 2 through the resistor 100.
Depending on the DC tuning voltage applied to 2
The receiving station for FM broadcasting is switched. Further, the transistor 40 is a transistor for local oscillation,
The signal converted to an intermediate frequency of 10.7MHz is sent to terminal 43.
It brings out more. Although the terminal 44 is a terminal for extracting the local oscillation frequency, it is not used in the conventional circuit shown in FIG.

FIG. 7 shows a specific example of the circuit configuration of the TV tuner 10 shown in FIG.
and a UHF antenna is connected to terminal 102. In this circuit configuration, terminal 103 is a power supply terminal supplied with power from DC power supply +B, and terminals 104 to 107 are control input terminals that receive command signals individually supplied from decoder section 2 shown in FIG. 4. Terminal 104 receives a signal commanding to operate VHF low band VL,
5 is a signal for commanding high band HL to operate;
106 are each supplied with a signal instructing the UHF tuner circuit to operate. And terminal 10
7 is applied with a predetermined DC tuning voltage for selectively receiving each channel. like this
Video intermediate frequency output from TV tuner 10 is terminal 1
Extracted from 08. Here, the terminal 109 is
Although this is a terminal for extracting the local oscillation frequency of the TV broadcast reception channel, it is not used in the conventional circuit shown in FIG.

Each tuning voltage in FIGS. 6 and 7 is created by the decoder section 2 as shown in FIG. 4, and a tuning voltage setting circuit 21 is provided to adjust this tuning voltage in advance. . Further, the control signals giving the above-mentioned commands cause the band switching section 22 to perform a switching operation by decoding the codes already mentioned by the decoder section 2, and are individually output from the band switching section 22. When the decoder section 2 decodes the selection command for FM broadcast or TV broadcast, the band switching section 22 outputs a broadcast selection signal so that the switches 23 and 24 switch the power supply line of the DC power supply +B. This selection signal also operates the selection switch 25 as shown in FIG. 4, and the intermediate frequency of the FM broadcast output from the FM tuner 3 is
10.7M of TV broadcast output from the second mixer 20
The intermediate frequency converted to Hz is selected according to the receiving broadcast mode.

In the conventional circuit shown in FIG. 4, the FM demodulated output of the audio intermediate frequency that is switched according to the receiving broadcast mode, in other words, the output of the demodulator 6, has a level that changes depending on the broadcast selection switch due to the difference in the modulation degree of each broadcast. It fluctuates with This variation in output level has not been resolved by the conventional volume adjustment circuit 7. That is, the conventional volume adjustment circuit 7 adjusts the DC voltage signal supplied via the initial volume adjustment circuit 26 and the muting circuit 27 in accordance with the volume control command to increase or decrease the volume decoded by the decoder section 2 described above. Therefore, the amplification gain is electronically controlled, and the initial volume adjustment circuit 26 is only given a common fixed value of this DC voltage signal in any reception mode of both broadcasts, and the decoder section 2 was simply a continuously changing value.

Figures 8 to 10 are block circuit diagrams showing the circuit configuration of an embodiment of the present invention that solves such problems, and Figure 4 shows the same or the same parts as the conventional circuit configuration to clearly demonstrate the simplicity of the present invention. Therefore, the same reference numerals are used.

The difference between the circuit configuration of the embodiment shown in FIG. 8 and the conventional circuit configuration shown in FIG. This is the point. As is well known, this tuning voltage is formed by a DC voltage signal with predetermined steps that vary depending on the selected channel, and is generally set so that the higher the receiving frequency, the larger the step voltage value. Therefore, the comparison reference voltage source 28
If the value of is set in advance to the step voltage value of the highest frequency of the FM tuning voltage, the comparator 29 compares the supplied tuning voltage with this reference voltage to determine whether the TV or
Generates a discrimination output for either FM broadcast reception mode. For example, if the tuning voltage is less than or equal to the reference voltage value, a discrimination output indicating FM broadcast reception mode is generated, and if it is larger, a discrimination output indicating TV broadcast reception mode is generated, and either one of the discrimination outputs is output to the initial volume adjustment circuit 26. Send to. In this case, since the initial volume adjustment circuit 26 knows the demodulated output levels of the FM broadcast and the TV broadcast in advance, it is configured to switch to one of these levels when in the other broadcast reception mode. FIG. 9 shows a specific example of a circuit for obtaining such reception mode discrimination output and switching the initial volume setting value as described above for the volume adjustment circuit 7 described above. In FIG. 9, a DC voltage signal for volume control is supplied from the decoder section 2 to a terminal 261, and the bias voltage of a transistor 262 is controlled in accordance with this signal. Therefore, the initial setting value of the DC voltage signal given to the volume adjustment circuit 7 is the volume 26.
3, and this volume is fixed thereafter. On the other hand, in this specific circuit example, the discrimination output of the above-mentioned comparator 29 is supplied to the terminal 264, but here the tuning voltage is directly applied, and the above-mentioned comparator 29 and comparison reference voltage source 28 are substantially It may also be configured such that the transistor 265 plays this role. For example, this transistor 2
If the bias voltage value for turning on the transistor 265 is set in advance to be somewhat larger than the tuning voltage of the highest frequency of the FM broadcast, the turning on of the transistor 265 becomes a discrimination operation in the TV broadcast reception mode. Therefore, transistor 265
By turning on, the initial setting value of the DC voltage signal previously set by the volume controller 263 during the off operation is changed to increase the demodulated output level for the volume adjustment circuit 7. If the tuning voltage drops to the FM broadcast receiving side, the transistor 265 is turned off, and the initial setting value is automatically changed again. The same holds true even if the transistor 265 is operated by the discrimination output of the comparator 29 shown in FIG. 8 described above.

FIG. 10 is a block diagram showing another embodiment of the configuration for automatically switching the demodulated output level as described above.
The differences from the circuit configuration shown in the figure are as follows. 1st
The difference in FIG. 0 is that the broadcast reception mode is discriminated by constantly monitoring the local oscillation frequency of FM or TV. This local oscillation frequency is converted into a rectangular pulse signal by the waveform shaping circuit 30 and then supplied to the counter 31 . The counter 31 counts the number of pulses of the above-mentioned pulse signal taken in one period of the clock pulse provided by the clock oscillator 32. Therefore, the clock pulse provided by the clock oscillator 32 here serves as a gate pulse for the counter 31, and is distinguished from the clock pulse that drives the counter 31. As a result, by setting the period of the clock pulse in advance, the counter 31 can make the number of pulses taken in, or in other words, the count value, correspond to a specific wave of the broadcast reception frequency. This particular wave in advance
When set to the highest receiving frequency of FM broadcasting, the carryout of the counter 31 becomes an output that discriminates the receiving mode of TV broadcasting. Therefore, by applying this discrimination output to the terminal 264 shown in FIG. 9, for example, the initial setting value of the volume adjustment circuit 7 can be automatically changed in the same manner as in the examples shown in FIGS. 8 and 9 already described. It can be performed.

As described above, according to the present proposal, the comparator 29
Alternatively, a discriminator including the counter 31 and the like, and a gain adjuster formed by the volume adjustment circuit 7 and the initial volume adjustment circuit 26 can always obtain a stable audio demodulation output in any broadcast reception mode. It is possible to eliminate complicated operations for the viewer.

[Brief explanation of the drawing]

Fig. 1 is a frequency allocation diagram showing the reception bands of TV broadcasting and FM broadcasting, Fig. 2 is a spectrum diagram showing the FM modulation degree, Fig. 3 is a characteristic diagram of the FM demodulator,
Figure 4 is a block circuit diagram showing the configuration of a conventional receiver, Figure 5 is a diagram showing the correspondence between key commands and transmission codes, Figure 6 is a circuit diagram of an FM tuner, and Figure 7 is a circuit diagram of a TV tuner. Fig. 8 is a block circuit diagram showing the configuration of a receiver according to an embodiment of the invention, Fig. 9 is a block circuit diagram showing an example of the circuit of the main part of the invention, and Fig. 10 is a receiver according to another embodiment of the invention. FIG. 2 is a block circuit diagram showing the configuration of the machine. Discriminator (29... comparator, 30... waveform shaping circuit, 31... counter, 32... clock oscillator), gain adjuster (26... initial volume adjustment circuit, 7... volume adjustment circuit).

Claims (1)

[Scope of utility model registration request] In TV and FM broadcast receivers that demodulate TV and FM broadcast audio signals using a shared demodulator,
a discriminator for discriminating between FM broadcast reception and TV broadcast reception by monitoring the tuning frequency or local oscillation frequency of the receiver; 1. A TV and FM broadcast receiver characterized in that a gain adjuster is provided at a subsequent stage of the demodulator to always control different demodulation output levels to a predetermined constant level regardless of the reception state of the broadcast.