JPS6043713B2 - Multi-format television receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to an audio intermediate frequency amplification circuit for a multi-system television receiver that allows television broadcasts of different broadcasting formats to be received by one television receiver.
The purpose is to switch between multiple systems using a simple circuit.

As is well known, the format of television broadcasting (hereinafter referred to as TV broadcasting) differs from country to country around the world, and the audio intermediate frequency (hereinafter referred to as SIF), reception frequency band, and screen field frequency are also different. It's summery. For example, the United States and European countries such as West Germany differ in the three points mentioned above, as shown in the table below.

To receive TV broadcasts in these different broadcast formats,
Either prepare separate receivers for each method, or
A method was devised in which two receivers could be used to switch to suit each system.

Particularly recently, small portable television receivers that operate on dry cell batteries have become available, and since these can be carried around the world, the latter method using a switch has no choice but to be used.

An example of a television receiver using such a method is shown in FIG.

In the figure, 1 indicates a tuner, and a signal tuned and extracted by the tuner 1 is selectively amplified by a band amplifier 2 and demodulated by a video detector 3. The demodulated signal is guided to the audio intermediate frequency amplification/detection circuit 4, where the audio is demodulated, amplified by the amplifier 5, and drives the speaker 14.

Further, the signal demodulated by the video detector 3 is applied to the video amplifier 6 and guided to the sync separation circuit 15.

Here, the synchronization signal is separated, and the vertical deflection circuit 7,
It is led to a horizontal deflection circuit 8 and supplied to a deflection coil 10 to deflect a cathode ray tube 9. Here, 11 is a flyback transformer, 12 is a high voltage rectifier, and 13 is a circuit for supplying a tuning voltage to the electronically tuned tuner 1. Here, the switches S1 to S4 are changeover switches for receiving television broadcasts of different broadcast formats, and the switches S1 and S2 are
is a switch for changing the resonance frequency according to the audio intermediate frequency, switch S3 is a switch for changing the receiving frequency band, and switch S4 is a switch for changing the amplitude according to the field frequency.

These switches S1 to S4 must all be switched in conjunction. In such a multi-system television receiver, the present invention is particularly intended to perform switching of the audio intermediate frequency amplification circuit by a simple means. Here, FIG. 2 shows a conventional example of switching the SIF section of a television receiver using the multi-system switching method described above.

In the figure, 41 is an audio demodulation circuit that supports one type (for example, 4.5 MHz); 2 is an audio demodulation circuit compatible with another system (for example, 5.5 MHz). In a television receiver with such a configuration, now,
When the SIF signal to be received is 4.5 MHz, by turning the switch 43 to the C side, the first audio demodulation circuit 4
The first audio demodulation circuit 41 was operated by supplying power only to point B, and an audio demodulated signal was obtained at point B.

In addition, conversely, the SIF signal applied to point A is 5.5MHz.
At that time, the switch 43 was turned to the D side to operate only the second audio demodulation circuit 42, thereby receiving different signals of each broadcasting system. In addition, 44 in the figure
, 45 are diodes for preventing mutual interference of the first and second audio demodulation circuits 41 and 42. However, switching broadcasting systems using this method requires only one switch, but requires audio demodulation circuits dedicated to each broadcasting system, and these demodulation circuits include transistors, integrated circuits, diodes, etc. It has the drawback of requiring active elements and many parts, making it expensive.

In other words, if you want to receive data using two systems, it will cost twice as much, and if you want to receive data using a triple system, it will cost three times as much, making it more expensive than just a single system. ) On the other hand, there was also a method of switching between these methods by using a common active element and switching a resonant circuit or the like.

Examples are shown in FIGS. 1 and 3. Here, an example will be shown in which an integrated phoneme intermediate frequency amplification/detection/wave circuit 20 is used as the active element for amplification and demodulation. Also 2
1 and 22 are filters corresponding to the respective broadcasting systems (for example, 21 = 4.5MHz filter, 22 = 5.5MHz filter)
z filter), 23, 24, 25 are switching diodes for switching each method, 26, 27, 28, 29, 3
0 is a resistor through which a switching current flows to turn on and off these switching diodes 23, 24, and 25;
31 and 32 are DC blocking capacitors for preventing this switching current from flowing into the integrated circuit 20;
, 34, 35 and 36 are capacitors and coils for forming a resonant circuit constituting the detection circuit, 37 is a bias resistor to the input terminal P of the integrated circuit 5, and 38 is a bypass capacitor. Now, when the signal is 5.5r1!4Hz as the audio intermediate frequency, the switches Sl and S2
When turned to the D and D'' sides, a switching current flows through the switching diode 24 through the resistors 27 and 28, the diode 24 becomes conductive, and the SIF signal (5.
5 MHz) is applied to the integrated circuit 20 through the filter 22, amplified, and guided to the resonant circuit of the detection circuit.

In the resonant circuit of the detection circuit, since no switching current flows through the diode 25, the coil 36 and capacitors 33, 3
4 to resonate with the SIF signal (=5.5 MHz), an audio demodulated signal can be obtained at the output point B. On the contrary, SIF
When 4.5 MHz is applied as a signal, it can be received by turning the switches Sl and S2 to the C and C'' sides.

At this time, the diode 23 is conductive, the diode 24 is cut off, and the SIF signal (4.5r!4HZ) is applied to the integrated circuit 20 through the filter 21.
The diode 25 also becomes conductive, and the capacitor 35 is connected in parallel to the capacitor 33, thereby lowering the resonant frequency of the detection circuit.

At this time, the resonance frequency is set to 5.5MH by the capacitor 35.
If the frequency is adjusted so as to change from z to 4.5 MHz, an audio demodulated signal can be obtained at the output point B. However, switching by this method requires two switches, and in the detection section, the resistances 29 and 30 for flowing the switching current reduce the Q of the detection circuit at resonance. However, there were drawbacks such as a decrease in amplitude modulation suppression ability.

Therefore, the present invention is intended to switch the method of an audio intermediate frequency amplified detection circuit with a simple configuration.

An example of this will be explained below using FIG. 4.

In the figure, parts that are the same as those in FIG. 3 are given the same numbers and will be explained. In FIG. 4, in the input section, the anodes of the first and second switching diodes 50 and 51 are connected to the input terminal P of the integrated circuit 20 via a common DC blocking capacitor 31, switching diode 50
, 51 are connected to the first terminals of the solid-state resonators 21 and 22, respectively. Then, the anodes of the first and second switching diodes 50 and 51 are grounded via a resistor 52 and a bypass capacitor 53 in order, and the connection point between the resistor 52 and the bypass capacitor 53 is connected to a DC power supply 54, and the first , second switching diode 5
A DC voltage is supplied to the anodes 0 and 51 via a resistor 52. On the other hand, in the detection section, 4.5MH
3rd solid state resonator 55 resonating at z and 5.5MHz
A fourth solid-state resonator 56 that resonates is provided, and the first terminals of these solid-state resonators 55 and 56 are both connected to one detection end r of the integrated circuit 20, and the second terminal is grounded. The resonance terminal of the integrated circuit 20 is connected to the other detection end q of the integrated circuit 20 via the third and fourth switching diodes 57 and 58. Here, the diodes 57 and 58 are inserted with their anodes on the detection end q side. The detection end q is an integrated circuit 2
is the output of the emitter follower transistor Q within 0,
Since the load current can be taken out stably, this is used as the third
, and used as a switching current supply source for the fourth switching diodes 57 and 58. The cathodes of the first and third switching diodes 50 and 57 are connected to one fixed terminal C'' of the switch S1 via resistors 59 and 60, respectively, and the cathodes of the first and third switching diodes 50 and 57 are connected to one fixed terminal C'' of the switch S1. Each cathode is connected to a resistor 61,6 respectively.
2 to the other fixed terminal D'' of switch S1. The movable terminal of switch S1 is grounded. Here, 63
, 64 is a bypass capacitor, and 65 is a resistor connected between the detection terminals Q and r.

Now, when switch S1 is turned to terminal C'' side, resistor 59,
60 is grounded, a switching current flows from the DC power supply 54 and the detection terminal q, and the switching diodes 50, 5
7 becomes conductive. Therefore, the solid-state resonators 21 and 55 with a resonance frequency of 4.5 MHz operate. At this time, since no switching current is supplied to the switching diodes 51 and 58, these diodes 51 and 58 are in a cut-off state, and the solid state resonators 22 and 22 with a resonant frequency of 5.5 MHz are
56 will not be affected in any way. That is, solid-state resonators 21 and 5 are connected to the input terminal p and the detection terminals Q and r, respectively.
Only 5 will be connected. On the other hand, when the switch S1 is turned to the terminal D'' side, the switching diodes 51, 5
8 becomes conductive, and only the solid-state resonators 22 and 56 are connected to the input terminal P1 and the detection terminals Q and r, respectively. As explained above, according to the present invention, it is possible to switch the input section and the detection section with one switch, and the configuration is simplified.

Further, according to the present invention, it is possible to provide a switching means without adjustment and without mutual interference. Furthermore, since the detection section does not require a special switching power supply, the configuration is further simplified.

[Brief explanation of drawings]

Figure 1 is a block diagram of a multi-system television receiver;
The figure shows a conventional switching method of the audio intermediate frequency amplification/detection circuit in the same receiver, Figure 3 shows another conventional switching method of the same circuit, and Figure 4 shows an implementation of the present invention. FIG. 2 is a circuit diagram of a main part of a multi-system television receiver in an example. 20... Integrated circuit audio intermediate frequency amplification
Detection circuit, 21, 22, 55, 56... Solid resonator, 50, 51, 57, 58... Switching diode, 59, 60, 61, 62... Resistor,
S1...Switch.

Claims (1)

[Claims] 1 Equipped with an integrated audio intermediate frequency amplification/detection circuit, the amplification stage of this circuit has an input terminal, the detection stage has two terminals, and the anodes of the first and second switching diodes are connected to direct current. The first and second switching diodes are connected to the input terminal via a blocking capacitor, and the cathodes of the first and second switching diodes are connected to first and second solid-state resonators having different resonant frequencies. The anode of the switching diode is connected to the power supply, and the first of the third and fourth solid-state resonators having different resonance frequencies is connected to the power supply.
The third and fourth terminals are connected to one terminal of the detection stage.
The second terminal of the solid-state resonator is grounded, and the anodes of the third and fourth switching diodes are connected to the other terminal of the detection stage to which the detection terminal voltage is supplied. The cathodes of the first and third switching diodes are connected to the common terminals of the third and fourth solid-state resonators, respectively, and the cathodes of the first and third switching diodes are connected to the first switching diode whose movable terminal is grounded through the respective resistors. and the cathodes of the second and fourth switching diodes are connected to the second fixed terminal of the changeover switch through respective resistors.