JPS5845879B2 - signal switching device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal switching device that can switch and output two types of signals based on a control signal.

Further, the present invention provides a suitable circuit arrangement for a dual-purpose color receiver capable of receiving both PAL and SECAM color broadcasts.

In the PAL-8ECAM dual-use color receiver, circuits for processing color signal components are provided in parallel for PAL and SECAM.

Color difference signals R-Y, G- reproduced by each circuit
Y, B-Y or primary color signals R2G, B are switched depending on the broadcasting system and applied to the output matrix or picture tube.

It is desirable that the switching device be automated, and one of the color killer output methods used in the circuits that process each color signal component can be used as a control signal, and the color difference signal or primary color signal can be switched accordingly.

However, if a synchronization error occurs when receiving or adjusting a weak electric field, the color killer output may fluctuate and show an unreliable value, so if switching is performed due to this, the screen will appear interrupted and become very unsightly. .

Furthermore, this type of switching circuit requires sufficient separation so that when one switched signal is being sent out, the other switched signal is never sent out to the output side.

The present invention is a signal switching device developed to satisfy the above requirements, and one embodiment thereof will be described with reference to FIGS. 1 and 2.

Tc is an input terminal to which a DC voltage including at least two values rising from a low second potential at or near zero to a predetermined high first potential is applied, and the transistor Q81
connected to the base of

Transistors Q81 to Q84 are connected in series,
The emitter of transistor Q83 is the first stage transistor Q
81 emitter.

Further, a parallel circuit of a resistor R83 and a capacitor C81 is provided between the emitters of the transistors Q81 and Q83 and ground.

These transistors Q81-Q90 generally operate as shown in FIG. 2 with respect to the DC input level applied to terminal Tc.

Therefore, when one of the first control voltage appearing at the output terminal T1 and the second control voltage appearing at the output terminal T2 is at a high level (hereinafter referred to as "H11"), the other power button -
level (hereinafter referred to as "L 11"), which have mutually opposite phases and contradictory aspects.

Now, when the transistor Q81 is in the off state, the transistor Q83 is turned on and charges the capacitor C81, so that its terminal voltage is applied to the emitter of the transistor Q81.

Transistor Q81 will not turn on unless the DC level at input terminal Tc exceeds the level determined by this emitter voltage.

Further, when transistor Q81 is turned on, transistor Q83 is turned off, and the charge in capacitor C81 is discharged through resistor R83.

Since transistor Q81 is on, the terminal voltage of resistor R83 appears at the emitter.

If this voltage is set close to zero potential, the terminal Tc
Transistor Q81 will not turn off unless the DC level of Q81 takes a value lower than the level determined thereby.

That is, transistors Q81, Q83, resistor R83
and capacitor C81 form a so-called window comparator circuit, and the input terminal TO takes an intermediate value between the upper and lower thresholds.
A dead zone is provided in which the output is not switched or reversed with respect to the DC level.

First and second control voltages obtained from terminals TI and T2 switch a switching circuit consisting of transistors Q85 to Q90.

Terminals TPR, TPO, and TPB connected to the collectors of transistors Q85, Q86, and Q87 are input terminals to which a PAL color difference signal or primary color signal is applied as a switched signal, and transistors Q88, Q89, and Q89. Q
Terminal TSR connected to the collector of 90.

TSG and TSB are input terminals to which SECAM color difference signals or primary color signals are applied.

Transistors Q85 and Q88, Q86 and Q89, Q87
The emitters of Q90 and Q90 are respectively led to common terminals TR, TG, and TB to send out switched signals.

Transistor Q85. Q86. A first control voltage obtained from terminal T1 is applied to the base of Q87, and the other transistor Q88°Q89. A second control voltage from terminal T2 is applied to the base of Q90.

Assuming that the DC input level applied to terminal Tc is the color killer output of the SECAM color signal processing circuit,
The voltage indicates a high first potential having a constant value when receiving the SECAM signal in normal operation;
When receiving the L signal, the second potential is a low potential close to zero.

Therefore, it operates as shown in FIG. 2, and the transistor Q
88°Q89. When Q90 is on, Q85. Q86. Q
87 is turned off, and SECAM color difference signals are sent out from output terminals TR, TG, and TB.

Conversely, when transistors Q85, Q86, and Q87 are on, Q88°Q89. Q90 is turned off and the PAL color difference signal or primary color signal is switched and sent out.

If the level of the color killer output drops unexpectedly when receiving SECAM broadcasts, please turn off the S
If it is set to send out ECAM color output, it will operate to send out the switched color output continuously unless it becomes lower than a predetermined threshold.

Although the above embodiment is applied to PAL-8ECAM output switching, it should also be possible to use it to switch other signals.

Also, the transistor Q85 of the switching circuit in FIG.
Q90 is at least one pair (for example, Q85 and Q88) when two switching signals are selected and switched.
Good to have.

As described above, the present invention has a first potential when one of two different broadcasting systems is selected and received, and has a second potential lower than the first potential when the other is selected and received. A DC voltage is generated, and by detecting the difference between the first and second voltages, it is determined which of the two broadcasting systems is being received, and based on this discrimination output, the system is being received. This embodiment embodies a signal switching device of a different type broadcast receiving apparatus that selectively supplies broadcast signals such as color difference signals to a circuit common to both types, such as an output L-IJ rack.

As described above, the present invention can provide a signal switching device that maintains the switching operation effectively even when the level of the broadcast signal fluctuates unintentionally and the level of the input DC voltage fluctuates.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of a signal switching device according to the present invention;
FIG. 2 is a working suit for explaining the operating mode shown in FIG. 1. Tc...Input terminal that provides changing DC voltage;
Q81-Q90...Transistor, T1 and T2...Terminal to take out control voltage, TPR, TP
G. TPB, TSR, TSG and TSB...Switched signal input terminals, TR, TG and TB...
...Output terminal for switched signals.

Claims (1)

[Scope of Claims] 1. Direct current that has a first potential when one of two different broadcasting systems is selected and received, and has a second potential that is lower than the first potential when the other is selected and received. By detecting the difference between the first and second potentials, it is possible to distinguish which of the two broadcasting systems is being received, and this discrimination output is used to determine which of the two broadcasting systems is being received. In a different type broadcast receiving device that selectively supplies a broadcast signal to a circuit common to both types, the upper limit threshold is lower than the first potential and higher than the second potential, and the upper limit threshold is lower than the upper threshold. A lower limit threshold higher than the two potentials is set in advance, and by comparing the lower limit threshold with the DC voltage generated upon reception of the broadcast, the potential of the DC voltage is set to the upper limit. The output signal is set as a first control voltage when the voltage becomes higher than the upper threshold from a voltage lower than the threshold, and the potential of the DC voltage changes from a voltage higher than the lower threshold to a voltage lower than the lower threshold. a control voltage generation circuit that sometimes sets the output signal as a second control voltage and does not change the voltage of the output signal when the potential of the DC voltage is other than the above; In the case of one control voltage, the broadcast signal of one of the two methods is supplied to the common circuit, and when the output signal of the control voltage generation circuit is the second control voltage, the broadcast signal of one of the two methods is supplied to the common circuit. In order to supply the broadcast signal of the other system to the common circuit, one of the broadcast signals of the two systems is selectively drawn out according to the first or second control voltage of the control voltage generation circuit. a switching circuit for switching between the first and second control voltage generating circuits, the control voltage generating circuit being a circuit for receiving the DC voltage in the receiving device;
By using the control voltage as a discrimination output in the receiving device, the signal switching operation of the switching circuit is prevented even if the potential of the DC voltage varies depending on the broadcast reception state, as long as it does not cross the upper or lower threshold. A signal switching device characterized by: