JPH0758601A - Duty controller - Google Patents

Abstract

PURPOSE:To improve the mounting of parts and the temperature characteristic by reducing the value of the integral constant as a constituting element of a duty adjustment device which can adjust the duty of an output pulse signal synchronized with an input pulse signal. CONSTITUTION:A pulse generating circuit generates a gate pulse signal S5, which has an arbitrary pulse width and whose position can be moved in one period T of an input pulse signal Sin by a variable resistance VR1, from the input pulse signal Sin. A switch circuit SW5 is controlled by a gate pulse signal S5 to open/close the circuit between a monostable multivibrator MMV 1 and the integrating circuit. It is sufficient if the integral constant has such value that the pulse width of the gate pulse signal S5 can be sufficiently integrated; and since the edge at the time, when the MMV 1 turns off the output pulse signal S1, exists in the gate pulse signal S5, the gate pulse signal S5 is moved in one period T of the input pulse signal Sin to control the duty of an output pulse signal Sout.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a duty adjusting device which outputs a pulse synchronized with an external input pulse and makes it possible to adjust the duty of this output pulse, and more particularly to an external input video synchronizing signal in a CCD camera having an external synchronizing function. The present invention relates to a duty adjusting device which is used as a horizontal phase adjusting circuit for an output image and the like when an input pulse has a long cycle.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing an example of a conventional duty adjusting device.

In FIG. 3, a monomultivibrator (MMV) 1 in which an input pulse signal Sin is input to a B input terminal
The pulse signal S1 from the Q-bar output terminal is a signal having an inverted phase synchronized with the input pulse signal Sin. This pulse signal S1 has resistances R2, R3, R4 and variable resistance VR2.
It is integrated by an integrating circuit including a capacitor C2 and an operational amplifier (OP) 4. This integrator circuit is M
A voltage corresponding to the duty of the pulse signal S1 from the MV1 is output. The voltage output from the integrating circuit is the resistance R1,
Since it is negatively fed back to MMV1 through the capacitor C1,
The output pulse signal Sout from the Q output terminal of MMV1 is controlled in pulse width.

The principle of duty control generation will now be described with reference to FIG.

FIG. 4 (a) is a diagram for explaining the principle of pulse generation in the mono-multivibrator, and FIG. 4 (b) is FIG.
6 is a diagram for explaining the principle of duty adjustment in FIG.

Referring to FIGS. 3 and 4 (a), the MM
At V1, charging starts from the rising edge or falling edge of the trigger pulse (input pulse signal Sin) by the time constant of the resistor R1 and the capacitor C1, and the capacitor C1
When the charged voltage reaches the threshold level Vth set inside the MMV1 in advance, it is discharged with a time constant of 0 and the capacitor C1 has no charge. The pulse signal S1 is output from the Q-bar output terminal of the MMV1 only during the time from the charging to the discharging of the capacitor C1.
Is output.

Next, referring to FIGS. 3 and 4 (b), when the duty of the pulse signal S1 increases, the DC voltage value of the signal S12 obtained by integrating the pulse signal S1 increases, and OP4
The potential of the output S13 of the V.sub.2 decreases from VA to VB. As a result, the voltage applied to the resistor R1 decreases, and the time required for the voltage applied to the capacitor C1 to reach the threshold level Vth is extended. Therefore, the output pulse signal S1 from the Q-bar output terminal of the MMV1 has a larger negative portion than the pulse A like the pulse B, that is, the duty decreases.

As described above, the M of the duty adjusting device is
When the duty becomes large, the MV1 is controlled so that the duty is decreased so as to prevent it, and conversely, when the duty is decreased, the control is increased so as to prevent it. That is, the duty is negatively fed back.

If this negative feedback system converges,
There should be a stable point at some duty value.

The output S13 of OP4 is + of OP4.
It changes according to the input voltage to the terminal. Specifically, if the input voltage of the + terminal is increased, the output voltage of OP4 decreases, and conversely, if the input voltage of the + terminal is decreased, the output voltage of OP4 increases. Therefore, the duty can be adjusted by adjusting the variable resistor VR2.

[0011]

In this conventional duty adjusting device, when the cycle of the input pulse signal Sin becomes long, the product of the resistance value of the resistor R2 and the capacitance value of the capacitor C2, that is, the time constant becomes large, and the MMV1 The gain of the negative feedback system that controls the duty of the pulse signal S1 output from the device becomes low. Therefore, the output pulse signal Sou
There is a problem that the duty of t becomes unstable.

[0012]

SUMMARY OF THE INVENTION A duty adjusting device of the present invention is a first mono-multivibrator which inputs a square wave signal having a predetermined period and outputs a first pulse signal which is a phase inversion of the square wave signal. And the square wave signal is input, the time delay with respect to the square wave signal is made variable, and the pulse width is defined to a value different from that of the square wave signal.
Gate pulse generating means for generating the pulse signal, sampling means for sampling the input first pulse signal with the second pulse signal, and an output voltage negative according to the duty ratio of the output signal of the sampling means. And a control means for controlling the pulse width of the first pulse signal by the output voltage of the integration means.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the duty adjusting device of the present invention, and FIG. 2 is a time chart of signals of respective parts in the embodiment shown in FIG.

The duty adjusting device of this embodiment uses an MMV1 which outputs a pulse signal S1 having an inverted phase from the Q bar output terminal by using the input pulse signal Sin of an arbitrary periodic square wave input to the B input terminal as a trigger. , Input pulse signal Sin of arbitrary periodic square wave input to B input terminal
And MMV2 that outputs a pulse signal S4 by changing the time delay with respect to the variable resistance VR1;
4 is defined by the resistor R5 and the capacitor C4 to a value different from the pulse width of the input pulse signal Sin.
A gate pulse generation circuit composed of MV3, a switch circuit (SW) 5 for sampling the input pulse signal S1 with a gate pulse signal S5, and an output S2 of SW5.
OP4 in which the output voltage changes as a negative characteristic in accordance with the duty ratio of the pulse signal of 1., the output voltage of OP4 is fed back to MMV1 through the resistor R1 and the capacitor C1, and the pulse width is controlled.

OP4 includes resistors R2, R3, R4 and a capacitor C2 to form an integrating circuit.

Next, the operation of this embodiment will be described with reference to FIG.

The MMV1 outputs the pulse signal S1 from the Q-bar output terminal using the input pulse signal Sin as a trigger.
The MMV2 outputs the pulse signal S4 from the Q-bar output terminal by using the input pulse signal Sin as a trigger. And MM
V3 uses this pulse signal S4 as a trigger to output a gate pulse signal S5 from the Q output terminal.

The pulse width tw1 of the pulse signal S4 can be changed by the variable resistor VR1. Therefore MMV3
The phase of the gate pulse signal S5 from the Q output terminal can be changed.

The pulse width tw1 determines the horizontal phase of the output video signal with respect to the horizontal synchronizing signal of the externally input video signal. That is, if the pulse width tw1 is long, the horizontal phase of the output video signal is delayed, and conversely, if the pulse width tw1 is short, the horizontal phase of the output video signal is advanced.

SW5 receives the pulse signal S1 from the Q-bar output terminal of MMV1, and turns on / off by the gate pulse signal S5 from the Q-output terminal of MMV3. That is, when the gate pulse signal S5 is at a high level (“H”), the pulse width tw of the gate pulse signal S5
The output S2 of SW5 is output as "H" only during the period of 2,
When the gate pulse signal S5 is at low level ("L"), the pulse signal S2 is in a high impedance state as shown by the broken line.

In addition to determining the damping factor of the loop, the pulse width tw2 can adjust the time constant of the integrator circuit in this loop. That is, the shorter the pulse width tw2, the smaller the time constant of the integrating circuit.

Next, in the integrating circuit composed of OP4, resistors R2, R3, R4 and capacitor C2, the output S2 of SW5 is input and integrated, but the gate pulse signal S5
If the pulse width tw2 of the input pulse signal Sin is sufficiently small, the time constant τ determined by the resistor R2 and the capacitor C2 becomes the input pulse signal Sin.
Output S3 of OP4 even if it is sufficiently smaller than the cycle T of
Can be regarded as a sufficiently smoothed DC voltage.

The DC voltage of the output S3 of OP4 is MMV.
1 is looped back through the resistor R1 and the capacitor C1 to control the pulse width of the pulse signal S1 from the Q bar output terminal of the MMV1 and the output pulse signal Sout from the Q output terminal, in other words, the duty. The control for the duty by this loop system is so-called negative feedback control for suppressing the change in the duty.

The principle of duty adjustment in FIG. 1 will be described.

The principle of the change of the pulse width of the pulse signal S1 from the Q-bar output terminal of the MMV1 due to the change of the output S3 of OP4 is as described in the above-mentioned principle of the conventional duty adjustment in FIG.

Also in the duty adjusting device of this embodiment, negative feedback is performed with respect to the duty. Considering the stable point of the negative feedback system, if the rising edge or the falling edge of the pulse signal S1 from the Q bar output terminal of MMV1 falls within the pulse of the gate pulse signal S5 from the Q output terminal of MMV3. If not, the output S2 of SW5 becomes "H" or "L", and therefore the output S2 of OP4.
3 becomes "L" or "H", and the negative feedback system does not converge.

Next, if the rising edge of the pulse signal S1 from MMV1 is within the pulse of the gate pulse signal S5, the potential obtained by integrating the output S2 of SW5 is the resistances R3 and R4.
The potential can be determined by the resistance division with. Therefore, there may be a stable point of the feedback system there. That is, the duty can be adjusted by adjusting the position of the pulse of the gate pulse signal S5.

When the falling edge of the pulse signal S1 is within the pulse of the gate pulse signal S5, the loop system is in positive feedback, and there is no stable point.

In the integrating circuit of this embodiment, it is sufficient that the pulse period (tw2 in FIG. 2) of the gate pulse signal S5 can be converted into the DC level, and therefore the integration constant is smaller than that of the integrating circuit of the conventional example shown in FIG. It becomes possible to do.

The resistance value of the resistor R2 and the capacitor C described above.
The fact that the time constant τ determined by the capacitance value of 2 is small means that the response characteristic of the integrating circuit does not have to be lowered, and therefore the pulse signal S of the MMV1 output is used.
1 and the response characteristics in the negative feedback system for controlling the duty of the output pulse signal Sout need not be lowered because the cycle T of the input pulse signal Sin is increased.

Therefore, according to this embodiment, even if the duty of the input pulse signal Sin changes due to jitter or the like, the output pulse signal Sou from the Q output terminal of the MMV1 is output.
It is possible to sufficiently suppress the change in duty of t.

[0033]

As described above, according to the present invention, the response characteristic of the negative feedback system for controlling the duty of the output pulse signal does not have to be lowered even if the cycle of the input pulse signal becomes large. Can be prevented from becoming unstable.

Further, since the integral constant value can be made small, a ceramic capacitor excellent in mounting space and temperature characteristics can be used, component mounting can be improved, and temperature characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a duty adjusting device of the present invention.

FIG. 2 is a time chart of signals of various parts in the embodiment shown in FIG.

FIG. 3 is a circuit diagram showing an example of a conventional duty adjusting device.

4A is a diagram for explaining the principle of pulse generation of the mono-multivibrator, and FIG. 4B is a diagram for explaining the principle of duty adjustment in FIG.

[Explanation of symbols]

 1, 2, 3 Mono multivibrator (MMV) 4 Operational amplifier (OP) 5 Switch circuit (SW) C1, ~ C4 Capacitor R1, ~ R5 Resistance VR1, VR2 Variable resistance S1, S4 Pulse signal S2 SW5 output S3, S13 Output of OP4 S5 Gate pulse signal S12 Integrated signal Sin Input pulse signal Sout Output pulse signal

Claims (5)

[Claims] 1. A first mono-multivibrator for inputting a square wave signal having a predetermined period and outputting a first pulse signal obtained by phase-inversion of the square wave signal, and the square wave signal for inputting the square wave signal. Gate pulse generating means for generating a second pulse signal having a variable time delay with respect to the signal and having a pulse width defined to a value different from the square wave signal, and the input first pulse signal to the second pulse. Sampling means for sampling with a signal, integrating means for changing the output voltage as a negative characteristic according to the duty ratio of the output signal of the sampling means, and pulse width of the first pulse signal with the output voltage of the integrating means And a control means for controlling the. 2. The gate pulse generating means defines a second mono-multivibrator for varying the time delay of the square wave signal, and a pulse width of the pulse signal of the second mono-multivibrator output for defining the first mono-multivibrator. The duty adjusting device according to claim 1, comprising a third mono-multivibrator which outputs two pulse signals. 3. The duty adjusting device according to claim 1, wherein the sampling means is a switch circuit which is turned on / off according to a high level / low level of the second pulse signal. 4. The duty adjusting device according to claim 1, wherein the integrating means comprises a resistor, a capacitor and an operational amplifier. 5. The duty adjusting device according to claim 1, wherein the control means is configured by feeding back an output voltage of the integrating means to the first mono-multivibrator.