Abstract:
A synchronizing signal separator in the circuit of a monitor selects between a composite synchronizing signal and a separate synchronizing signal under the control of a priority order stage, and it separates a composite synchronizing signal into a vertical synchronizing signal and a horizontal synchronizing signal. The priority order stage cuts off a composite synchronizing signal when a composite synchronizing signal and a separate synchronizing signal are concurrently detected.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a synchronizing signal separator in a monitor circuit and more particularly to a synchronizing signal separator distinguishing between a composite synchronizing signal and a separate synchronizing signal and, sending out a vertical or a horizontal synchronizing signal separately according to a designated priority order. 
     Conventionally, in order to send out to a desired place a horizontal synchronizing signal, a vertical synchronizing signal and a composite synchronizing signal of the horizontal synchronizing (H-Sync) signal and the vertical synchronizing (V-Sync) signal, switching by a separate connector or switch should be employed in accordance with a given input signal. In other words, an appropriate input terminal must be selected according to the kind of the input signal. As these various input signals had to be selected manually rather than automatically, it gave rise to a problem which frequently made the circuit unstable when a surge voltage occurred during its operation. 
     SUMMARY OF THE INVENTION 
     Thus, an object of the present invention is to provide a synchronizing signal separator contrived to send out a vertical synchronizing signal and a horizontal synchronizing signal separately when a composite synchronizing signal thereof and each separate synchronizing signal are concurrently input according to a given priority order, depending on input condition of the composite synchronizing signal and the respective separate synchronizing signal. 
     According to an aspect of the invention, the signal separator for separating synchronizing signals includes a first detector for detecting input of a composite synchronizing signal, a second detector for detecting input of a separate horizontal synchronizing signal, a priority deciding stage for cutting off output cf the first detector when the separate synchronizing signal and the composite synchronizing signal are detected at the same time, a horizontal synchronizing signal generator for generating the horizontal synchronizing signal from the first detector or the second detector under the control of the priority deciding means, means for passing the horizontal synchronizing signal through a lowpass filter and a vertical synchronizing signal generator for generating the vertical synchronizing signal by comparing an output from the lowpass filter with the separate vertical synchronizing signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawing, in which FIG. 1 is a circuit of an embodiment construction according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     EXAMPLE I 
     Assuming that only composite synchronizing signals are input into the first input terminal 1 of composite synchronization detector 10 as a first case, the deflecting synchronizing signal of the composite synchronizing signal which is input in a negative condition is inversely amplified by the first transistor Q1 via the first coupling condenser C1 and is detected at the emitter of the second transistor Q2 used as a buffer. 
     The detected signal is applied to the base of the third transistor Q3 via the second coupling condenser C2. So, the third transistor Q3 operates with its base potential attaining a logic high level. As a result, the output of the first exclusive OR gate G1 whose one input terminal keeps logic high level at all times and whose other input terminal is connected to the output terminal of the third transistor Q3 generates a logic high level detection signal S1 according to the operating characteristics of exclusive OR gate G1. 
     The reason is that one terminal of the first exclusive OR gate G1 is connected to a signal in logic high level at this time causes the output of the first exclusive OR gate G1 to generate a detection signal S1 according to whether there is a composite synchronizing signal in the input terminal or not. 
     Therefore, if no deflecting synchronizing signal of a composite synchronizing signal is applied to the first input terminal 1, no signal is applied to the third transistor Q3. Thus, a signal in logic high level is applied to both of the input terminals of the first exclusive OR gate G1 and its output terminal attains a low level without detecting a composite synchronizing signal. It is because bias voltage caused by the two resistances R6, R7 which establish the base potential level of the third transistor Q3 by being connected to supply power source terminal Vcc cannot reach operating voltage VT expressed by the formula (1) in case the third transistor Q3 does not operate because no signal is applied to the base of the third transistor Q3 through the second coupling condenser C2. ##EQU1## 
     On the other hand, the output signal S1 of the first exclusive OR gate G1 in logic high level is inversely amplified by the seventh transistor Q7 through resistance R18. As a result, it sends a horizontal synchronizing signal to the first output terminal 4, and the output signal at the collector of the seventh transistor Q7 is input to one terminal of the fourth exclusive OR gate G4 by being inversely amplified by the eighth transistor Q8 via the low-pass filter consisting of two resistances R20, R21 and two condensers C7, C8. 
     Although the other terminal of the fourth exclusive OR gate G4 is arranged to receive an input vertical synchronizing signal by being connected to the third input terminal 3, it is assumed that only the composite synchronizing signals are input in this time. Since a vertical synchronizing signal is not input from the third input terminal 3 and only the vertical synchronizing signal separated from the composite synchronizing signal is output to the second output terminal 5 via the fourth exclusive OR gate G4. 
     EXAMPLE II 
     As a second case, an account of the instance is given, in which a horizontal synchronizing (H-Sync) signal is input to the second input terminal 2 without an input of a composite synchronizing signal and of a vertical synchronizing signal is input separately to the third input terminal 3, the second exclusive OR gate G2 with its one terminal connected to the second input terminal 2 generates an output synchronizing signal according to the input signal from the second input terminal 2 due to grounding of the other terminal of the exclusive OR gate G2. 
     When a horizontal synchronizing signal is input to the second input terminal 2 to attain a logic high level, an output in logic high level is generated from the second exclusive OR gate G2 according to the operating characteristics of the exclusive OR as stated above, and applied to the base of the fifth transistor Q5 through resistance R12. 
     At this juncture, the fifth transistor Q5 will not operate because the base potential level is logic high, and the emitter stays at a logic high level owing to supply voltage Vcc. 
     So, collector voltage in logic high level of the, fifth transistor Q5 is low-pass-filtered through the integral circuit consisting of a resistance R13 and a condenser C6, and turns the sixth transistor Q6 on with the help of zener diode ZD1 and resistance R14. 
     Consequently, since current of supply voltage Vcc is bypassed via the collector and the emitter of the sixth transistor Q6, one terminal of the third exclusive OR gate G3 attains a low level, while a horizontal synchronizing signal detected from the second exclusive OR gate G2 is in the other terminal thereof. The output of the third exclusive OR gate G3, depending upon the state of H-synchronizing signal, is inverted and sent to the first output terminal 4 through the base and collector of the seventh transistor Q7. As the horizontal synchronizing signal comprising such a high frequency component cannot pass through the low-pass filter 41, the eighth transistor Q8 does not operate and the fourth exclusive OR gate G4 with its one terminal connected to the collector of the eighth transistor Q8 depends on the condition of vertical synchronizing signal input to the other terminal of the fourth exclusive OR gate G4 through the third input terminal 3 and a vertical synchronizing signal is finally output to the second output terminal 5. 
     EXAMPLE III 
     As a third case, an account of the instance is given, in which a composite synchronizing signal is input to the first input terminal 1 and, at the same time, a horizontal synchronizing signal is input to the second input terminal 2 and a vertical synchronizing signal is input to the third input terminal 3. 
     First of all, when a composite synchronizing signal and a separate synchronizing signal are input at the same time, it gives rise to a problem in deciding the priority order between the composite synchronizing signal and the separate synchronizing signal. Here, priority is given to the separate signal. 
     In other words, in case the output terminal of the second exclusive OR gate G2 attains a logic high level due to the horizontal synchronizing signal input to the second input terminal 2, the fourth transistor Q4 in the priority order decision stage 20 operates and the composite synchronizing detection signal S1 from the first exclusive OR gate G1 is bypassed through the collector and emitter of the fourth transistor Q4. So, the composite synchronizing signal is thereby cut off by the priority decision stage 20 and only the synchronizing signals are output to both of the two output terminals 4, 5 by the seventh transistor Q7 as in the second case, namely, a horizontal synchronizing signal is presented in the first output terminal 4 and a vertical synchronizing signal input to the third input terminal 3 is output via the second output terminal 5. Thus, priority is given to the separate synchronizing signals. 
     Such being the case, the present invention has advantages in that it upgrades and automates the product by automatically distinguishing between a composite synchronizing signal and a separate synchronizing signal and sending out such signals separately according to the order of priority.