JPS5822347Y2 - synchronous oscillation circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a synchronous oscillation circuit that applies a synchronizing signal from the outside to an oscillator that oscillates at a free-running frequency to synchronize it with the external signal frequency.

When synchronizing a free-running oscillator, such as an emitter-coupled astable multivibrator, by applying a synchronizing signal to it, when the free-running frequency is lower than the human signal frequency, the synchronizing range is determined according to the amplitude of the synchronizing signal. Within the synchronization range, the oscillator frequency becomes the frequency of the external input signal.

On the other hand, when the free-running frequency is higher than the input signal frequency, no synchronization occurs, and the oscillator frequency becomes approximately equal to the free-running oscillation frequency.

FIG. 1 is a diagram showing an oscillator for a vertical deflection circuit of a conventional television receiver, which is suitable for semiconductor integrated circuits.
is a terminal to which a negative direction vertical synchronizing signal is applied; 2 is a transistor that inverts and amplifies the vertical synchronizing signal; 3 and 4 are transistors that further amplify the signal inverted and amplified by transistor 2; 5, 6, and 7 are transistors. 3 and 4
8 is a transistor for further inverting and amplifying the signal made constant by these diodes; 9 is a transistor for further inverting this signal; 10 is a transistor for further inverting and amplifying this signal;
, 11.12, 13.14 and 15 are transistors 9
16 and 17 are emitter follower transistors, and 18 and 19 are the main components of the astable multivibrator. Transistors 20, 21 and 22 are resistors and capacitors that determine the time constant of the scanning period, 23 and 24 are resistors that together with the capacitor 22 determine the time constant of the blanking period, and 25 and 26 are resistors that shorten the time constant of the blanking period. transistors and resistors for
27 is a transistor that conducts when the transistor 18 is conductive to make the transistor 25 conductive;
is a transistor that amplifies the vertical oscillation output, and the vertical oscillation output is taken out from the terminal 29 or 30.

Note that 31 and 32 are power supply terminals.

FIG. 2 is a diagram showing the relationship between the free-running frequency of the oscillator for vertical deflection circuits and the input signal frequency, where the vertical axis f is the output frequency of the oscillator, the horizontal axis jA is the free-running oscillation frequency, and f5
is the synchronization signal frequency.

That is, as mentioned above, when the free running frequency is lower than the human power signal frequency, J within the synchronization range W.

is the input signal frequency, that is, the synchronization signal frequency fs,
On the other hand, when the free running frequency is higher than the input signal frequency, f
l is approximately equal to ha.

By the way, in the circuit shown in FIG. 1, when the free-running frequency is changed to be higher than the synchronized state by changing the resistor 21, so-called jitter occurs in which the leading or trailing edge of the waveform fluctuates near the limit where synchronization is lost.

The occurrence of this jitter is due to the presence of the input synchronization signal even after the oscillator inverts.

FIG. 3 shows the oscillation waveform of the transistor 18 in the circuit of FIG. 1. When the free-running frequency is lower than the synchronizing signal frequency, the synchronizing signal component S is immediately after the inversion of the waveform, as shown in FIG. 3a. exists in

On the other hand, when the free-running frequency is equal to the synchronizing signal frequency, the input synchronizing signal component S moves from the position immediately after the inversion as shown in the figure, moves further, and as shown in figure C, the input synchronizing signal component S If the trailing edge contacts, re-inversion is affected and the free-running frequency decreases.

In such a state, the free-running frequency becomes unstable, and the input synchronization signal disturbs the free-running frequency, causing jitter.

This jitter appears on the screen of a television receiver as vertical shaking, and when the value of resistor 21 is changed using the vertical synchronization knob, the screen becomes extremely unsightly. Put it away.

The present invention was developed to reduce such jitter, and is characterized by feeding back the output voltage of the oscillator to the synchronous input circuit.

The present invention will be explained below along with examples according to the drawings.

FIG. 4 is a block diagram showing the principle of the synchronous circuit according to the present invention, in which 33 is a synchronous signal input terminal, 34 is a synchronous signal processing circuit section, 35 is an oscillation section, and 36 is an oscillation output terminal. 37 is a feedback circuit.

According to the present invention, the feedback through the feedback circuit described above has the effect of eliminating the presence of the synchronous signal component, especially the trailing edge, in the oscillator when the free-running frequency is equal to or higher than the input synchronous frequency. , the causes of jitter are removed.

Next, the present invention will be explained based on a specific circuit diagram according to the present invention.

FIG. 6 is a diagram showing an embodiment of the present invention. The difference from the conventional circuit shown in FIG. 1 is that a resistor 38 and a capacitor 3 are connected between the oscillation output terminal 30 and the base of the transistor
A feedback circuit consisting of 9 is added.

Note that the synchronization input signal is connected to the resistor 40 and capacitor 4 from terminal 1.
However, in television receivers, the synchronization input signal is a combination of horizontal and vertical synchronization signals, and The integrating circuit operates to separate only the signals.

In this circuit, when a positive pulse is generated at the terminal 30 as a free-running oscillation output, this pulse is also applied to the base of the transistor 2 through the feedback circuit.

Therefore, the transistor 2 is cut off, and the transmission of the synchronous human input signal to the oscillation section is cut off.

Therefore, the phenomenon that causes jitter as shown in FIG. 3C is reliably eliminated.

FIG. 5 shows the waveform at the coupling point of the oscillation output and the synchronous signal in such a synchronous circuit, where a is the synchronous input signal, b is the oscillation output applied to the terminal 30, and C is the combined signal of both signals. This is a signal waveform applied to the base of transistor 2.

As is clear from this waveform, after the oscillation output is generated, the application of the synchronizing input signal, especially the trailing edge, to the oscillator is cut off for a period of time determined by the time constant of the oscillator.

FIG. 7 shows another embodiment of the present invention, in which the terminal 2
The oscillation output generated at terminal 9 and terminal 30 causes transistors 42, 43, 44 and 45 to operate as switches, thereby cutting off the application of the synchronous input signal to the oscillator for a predetermined period of time.

That is, in this circuit, the polarities of the oscillation outputs generated at terminals 29 and 30 are opposite, so when a positive oscillation output is generated at terminal 30, transistors 42 and 43 become conductive, and the output of transistors 2 or 4 is It acts to short-circuit the ends, while transistors 44 and 45 are cut off, and they act to open the base bias circuits of transistor 4 and transistor 9.

Although transistors 42 to 45 are arranged in this circuit, if any one of transistors 42 to 45 is present, the effect of cutting off the transmission of the synchronization input signal is achieved.

As explained above, in the present invention, by adding a very simple feedback means, the application of the synchronization input signal to the oscillation unit is interrupted by the oscillation output for a predetermined period of time. It is possible to suppress jitter caused by the influence of the trailing edge of the input signal, and the screen does not become unsightly even when the synchronization knob is changed.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional synchronous circuit including a free-running oscillator, Fig. 2 is a diagram for explaining the synchronization range, Fig. 3 is a diagram showing the oscillation waveform in the conventional circuit, and Fig. 4 is a diagram of the present invention. FIG. 5 is a waveform diagram of the connection point between the oscillation output and the synchronization signal in the circuit of the present invention, and FIGS. 6 and 7 are circuit diagrams of the present invention. 1... Synchronization signal application terminal, 18.19...
・・Astable multivibrator transistor, 20,2
1.23.24...Resistance for determining time constant, 22.
...Capacitor for determining time constant, 29.30...
...Oscillation output terminal, 31.32...Bias supply terminal, 38.39...Feedback resistor and capacitor, 42.43, 44, 45...For feedback transistor.

Claims (1)

[Scope of utility model registration request] A synchronous signal processing circuit section that processes a synchronous signal applied to an input terminal, and a free-running oscillation frequency that receives a synchronous signal output from the circuit section and generates an oscillation output synchronized with the synchronous signal frequency. A synchronous oscillation circuit, characterized in that a jitter suppression feedback means is provided between an oscillation output terminal of the free-running oscillation circuit section and the synchronous signal processing circuit section.