JP3154187B2 - Switching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching device provided in a receiving device for receiving signals of two systems and switching to one of the signals of the two systems.

[0002]

2. Description of the Related Art Normally, as a receiving apparatus for receiving both signals of an analog signal and a digital signal, for example, a NICAM (near instant signal) used in Europe is used.
aneouscompand audio multiplex) There is a receiving apparatus that receives two types of audio signals, a digital audio signal and an FM audio signal. This receiving apparatus normally receives a NICAM digital audio signal, but demodulates an analog audio signal which is an FM audio signal in accordance with the magnitude of an error pulse by a parity check of a digital decoding circuit for decoding the NICAM digital audio signal. A switching device that performs switching control so that the output signal of the analog demodulation circuit is used as an audio signal is required.

FIG. 4 shows a conventional switching device that has been considered. 4, the conventional switching device, for example, an input terminal 51 for error pulse is supplied from the digital decoding circuit, a resistor R ₁ connected to the input terminal 51, the resistor R ₁ is connected to the base emitter An output switching transistor TR _{1 of} an npn type, which is grounded; a capacitor C ₁ having one end connected between the resistor R ₁ and the output switching transistor TR ₁ and the other end grounded; a resistor R ₂ to the other end one end is connected between one end and the switching transistor TR ₁ of C ₁ is grounded, the resistor inserted between the switching transistor TR ₁ the collector and the positive power source B for the output with a R _3, and an output terminal 52 to derive an output, for example, an unillustrated control unit such as from the collector of the switching transistor TR ₁ .

[0004] In the conventional switching device of FIG. 4, for example, the average DC level of the input voltage v _i such error pulse v _i ^* with respect to the switching transistor TR
₁ base voltage v _b is the value of the capacitor C ₁ is sufficiently large, the following equation (1).

[0005]

(Equation 1)

[0006] The switching transistor when the value of v _b shown by the above equation is greater than the base-emitter voltage V _BE of the switching transistor TR ₁ TR ₁
Is turned on, and the output derived from the output terminal 52 becomes “L”.

[0007]

[SUMMARY OF THE INVENTION] In the conventional switching device shown in FIG. 4, for example, so-called Suresshi the input signal level, such as an error pulse is one of the threshold is not whether the switching transistor TR ₁ is operated When at the hold level, the switching transistor T
The operation of the R ₁ becomes unstable repeatedly turned on and off.

Therefore, a switching device according to the present invention has been made in view of the above-described circumstances, and by providing an appropriate hysteresis to a circuit operation,
An object of the present invention is to provide a switching device that stabilizes circuit operation by avoiding unnecessary switching on and off of a switching transistor.

[0009]

A switching device according to the present invention is provided in a receiving device to which both signals of an analog signal and a digital signal are transmitted, and decodes the digital signal. A switching device that switches between an analog output from an analog demodulation circuit that demodulates the analog signal and a digital output from the digital decoding circuit in accordance with an error pulse from the digital decoding circuit. The object of the present invention is solved by including an integrating section for integrating and a hysteresis switching section for giving hysteresis to an integrated output from the integrating section.

[0010] The hysteresis switching section may connect an output terminal of the first output switching element to a second output terminal.
The above-mentioned problem is solved by connecting the control terminal of the first switching element and the output terminal of the second switching element to the input terminal of the first switching element.

[0011]

According to the present invention, a circuit is provided by feeding back the output of the first switching element for output to the control terminal of the second switching element and the output of the second switching element to the input terminal of the first switching element. Hysteresis is applied to the operation to stabilize the operation near the threshold level.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the switching device according to the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram in which the first embodiment of the switching device according to the present invention is applied to an audio circuit system of a television receiver having a function of receiving a NICAM stereo broadcast.

The above-mentioned NICAM stereo broadcast is a digital audio multiplex broadcast, and this digital audio signal is transmitted by performing QPSK (four-phase modulation) on a subcarrier different from the FM broadcast.

In FIG. 1, a television wave received by a receiving antenna 15 of a television receiver is an analog audio signal F by a front end 16 such as a tuner, a video intermediate frequency amplifier and an audio intermediate frequency amplifier.
M audio signals and NICAM audio signals, which are digital audio signals, are supplied via an input terminal 1 to an audio circuit system having a reception function of the NICAM stereo broadcast. The FM audio signal is demodulated by the FM demodulator 2. The NICAM audio signal is decoded by the NICAM decoder circuit 3. Since the NICAM stereo broadcast is a digital audio broadcast, the NICAM decoder circuit 3 has a parity check function, and supplies an error pulse to the input terminal 11 of the switching device 4 according to the present invention when there is an error. The error increases due to a decrease in the level of the television signal and the like, and the error pulse also increases. An “L” or “H” signal is output to the control circuit 5 from the output terminal 12 of the switching device 4 depending on the average DC level of the input voltage of the error pulse supplied to the input terminal 11. The control circuit 5 controls the audio switch 6 based on “L” or “H” output from the switching device 4. The audio switch 6 switches between an FM audio signal, which is an analog audio signal, and a NICAM audio signal, which is a digital audio signal, under the control of the control circuit 5 and supplies it to the amplifier 7. One of the FM audio signal and the NICAM audio signal supplied to the amplifier 7 is generated as a sound from the speaker 8.

Next, a specific circuit configuration of the first embodiment of the switching device 4 will be described. NI shown in FIG.
In the audio circuit system of a television receiver having a CAM stereo broadcast receiving function, the switching device 4
Includes an input terminal 11 for error pulses from the NICAM decoder circuit 3 is supplied, a resistor R ₁ connected to the input terminal 11, a npn-type emitter the resistor R ₁ is connected to the base is grounded A first switching transistor TR ₁ , a capacitor C ₁ having one end connected between the resistor R ₁ and the first switching transistor TR ₁ and the other end grounded, the resistor R ₁ and the first
The resistor R ₂ having one end the other end is connected to ground between the switching transistor TR _1, a resistor R ₂ that is inserted between the first collector and the supply voltage B of the switching transistor TR _1, the output from the first collector of the switching transistor TR ₁ control circuit 5
An output terminal 12 for supplying the said first collector via a switching transistor TR based on the resistance R ₂ of ₁ is connected, the base to the output terminal 12 is connected, the npn-type emitter is grounded terminal 2 switching transistors TR ₂ . Here, an integrator 13 for obtaining an average DC level by integrating the input voltage of the error pulse supplied from the NICAM decoder circuit 3 via the input terminal 11 is indicated by a broken line portion composed of the resistor R ₁ and the capacitor C _1. It is. Further, the resistance R ₄ and the second
Broken line composed of a switching transistor TR ₂ of a hysteresis switching portion 14 to have a hysteresis circuit operation of the switching device 4.

[0016] Next, the operation of the first embodiment of the switching device according to the present invention with reference to FIG. 2 showing an input level versus output characteristics of the switching transistor TR ₁ for output as in FIG. 1. First, if the resistance R ₄ on circuit switching device 4 shown in FIG. 1, when the second no switching transistor TR _2, the average DC input voltage v _i of the error pulses supplied from the NICAM decoder circuit 3 level v _i ^* the first base voltage of the switching transistor TR ₁ for the output to v _b will equation (1) described above and the value of the capacitor C ₁ is sufficiently large. This is because the second switching transistor TR
_This is equivalent to the state where ₂ is off. The first switching transistor TR ₁ when for the output value of the base voltage v _b is greater than the base-emitter voltage v _BE of the first switching transistor TR ₁ for the output of the equation (1) is turned on Output is "L".

Meanwhile, when there is an error pulses supplied via the input terminal 11 is smaller than the level, the first switching transistor TR ₁ base voltage v for output
_b is the output first switching transistor T
Since the voltage is lower than the base-emitter voltage v _{BE of} R _1, the output first switching transistor TR ₁
Is off, and the output from the collector is "H". Signal of "H" is to be supplied to the second base of the switching transistor TR _2, the resistor R ₄ is grounded. Accordingly, the base voltage v _b of the first switching transistor TR ₁ for the output is represented by the following formula (2).

[0018]

(Equation 2) Here, R ₂ // R ₄ in the equation (2) is (R ₂ R ₄ ) /
(R ₂ + R ₄ ).

Since R ₂ // R ₄ in the above equation (2) is smaller than the resistance R ₂ , the base voltage v _b of the first switching transistor TR ₁ for output is equal to the _first voltage for output of the first switching transistor TR 1. for larger than the base-emitter voltage v _bE switching transistor TR _1, the average DC level voltage v _i ^* is the input voltage v _i of the error pulses to be supplied to the input terminal 11, the aforementioned formula (1) Must be larger than the case.

[0020] That is, Suresshi when the state of the output average DC level voltage v _i ^* is "large" of the input voltage v _i of the error pulse is "L" is the average DC level voltage v _i ^* decreases hold level v _ia ^* and, the average DC level voltage v _i ^* are threshold hold level when the average DC level voltage v _i ^* is the state of the output is "H" in "small" continue to increase v _ib * There is a difference between and as shown in FIG. That is, the input level has a hysteresis as shown in FIG.

As described above, by adding the resistor R ₄ and the second switching transistor TR ₂ as the hysteresis switching section 14, the circuit operation of the switching device can be provided with a hysteresis. Alternatively, the switching from analog voice to digital voice becomes smooth, and unnecessary switching does not occur many times even when the input signal is unstable.

Therefore, this switching device 4
A hysteresis circuit operation by the hysteresis switching unit 14, it is possible to eliminate the unstable operation near the first threshold value of the switching transistor TR ₁ for the output due to small variations in input, for example, NIC
If the error quality of the AM voice is large and the sound quality deteriorates, the first switching transistor TR for output is used.
_{From step 1} , "L" is supplied stably to the control circuit 5, and the control circuit 5 switches the voice switch to the FM voice side.

Next, a second embodiment of the switching device according to the present invention will be described with reference to the drawings. FIG. 3 is a diagram showing a second embodiment of the switching device according to the present invention. In FIG. 3, a switching device according to a second embodiment of the present invention includes a resistor R connected to an input terminal 41.
_41, the resistor R ₄₁ is connected to the base, the collector is grounded through a resistor R _44, a first switching transistor TR ₄₁ for the pnp type output emitter connected to the power supply voltage B, the resistance One end is connected between R ₄₁ and the base of the first switching transistor TR ₄₁ ,
A capacitor C ₄₁ whose other end is grounded,
₄₁ and the first switching transistor TR ₄₁
Of is connected to one end between the base, and a resistor R ₄₂ to the other end connected to the power supply voltage B, the first emitter base connected to the collector of the switching transistor TR ₄₁ is connected to the power supply voltage B, the second switching transistor T of the pnp connected the base of the first switching transistor TR ₄₁ collector via a resistor R ₄₃
Provided with R _42, and an output terminal 42 commonly connected to the base of the first collector and the second switching transistor TR ₄₁ of the switching transistor TR ₄₂ for the output.

In the second embodiment of the switching device according to the present invention shown in FIG. 3, when the level of the input signal input to the input terminal 41 is lower than a certain value, the first switching transistor TR for output is used. Hysteresis is given to the circuit operation when ₄₁ is turned on.

[0025] lower than a certain level input signal inputted to the input terminal 41, the first switching transistor TR ₄₁ for the output is on and the output is "H"
It has become. Signal of "H" is supplied to the base of the second switching transistor TR _42, the second switching transistor TR ₄₂ is a switching transistor TR ₄₂ of the resistor R ₄₃ and the second becomes off,
Will be shut off. On the other hand, if higher than a certain level input signal inputted to the input terminal 41, the first switching transistor TR ₄₁ for this output is turned off, the output is "L". This “L” signal is the second signal.
Is the supply to the base of the switching transistor TR _42, the second switching transistor TR ₄₂ is turned on, the base of the first switching transistor TR ₄₁ for the output signal of "H" is supplied.

[0026] That is, the second embodiment of the switching device according to the present invention has a hysteresis in the circuit operation due to the hysteresis switching unit 43 composed of the resistor R ₄₃ and the second switching transistor TR _42, the First switching transistor TR for output
Unstable operation occurring near the threshold value of ₄₁ can be eliminated.

Note that the switching device according to the present invention comprises:
It goes without saying that the present invention is not limited to the above embodiment.

[0028]

According to the switching device of the present invention, the error pulse from the digital demodulation circuit is integrated by the integration unit.
Since the hysteresis switching section provides the circuit operation with the hysteresis, the operation with the hysteresis can be easily performed at low cost and with few components. Further, the width of the hysteresis can be easily controlled by changing the value of the circuit element. Furthermore, by providing the circuit operation with an appropriate hysteresis, unnecessary repetition of ON / OFF can be avoided, the circuit operation can be stabilized, and the usability can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a switching device according to the present invention.

FIG. 2 is a diagram showing an input signal versus output characteristic of a switching device according to an embodiment of the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the switching device according to the present invention.

FIG. 4 is a circuit diagram of a conventional switching device.

[Explanation of symbols]

 2 FM demodulation circuit 3 NICAM decoder circuit 4 Switching device 5 Control circuit 6 Voice switch 7 Amplifier 8 ····· Speaker 13 ························· Hysteresis switching

Claims (2)

(57) [Claims] An analog signal and a digital signal are provided in a receiving device to which both signals are transmitted, and the analog signal is converted in accordance with an error pulse from a digital decoding unit for decoding the digital signal. A switching device for switching between an analog output from an analog demodulation unit for demodulation and a digital output from the digital decoding unit, wherein the integration unit integrates an error pulse supplied from the digital decoding unit, and the integration from the integration unit. A switching device comprising: a hysteresis switching unit that provides hysteresis to an output. 2. The hysteresis switching section connects an output terminal of an output first switching element to a control terminal of a second switching element, and connects an output terminal of the second switching element to an output terminal of the first switching element. 2. The switching device according to claim 1, wherein the switching device has a configuration for connecting to an input terminal.