JPH0342777Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a synchronization signal detection circuit for detecting horizontal synchronization signals and the like in video tape recorders, video disk players, and the like.

[Summary of the idea]

This invention is a synchronization signal detection circuit, which includes a frequency-voltage converter that converts the frequency of an input synchronization signal into a voltage, a trapezoidal wave generation circuit that generates a signal whose voltage changes in a trapezoidal waveform, and an output of the frequency-voltage converter. a comparator for comparing the output of the trapezoidal wave generating circuit with the output of the trapezoidal wave generating circuit; a first reset pulse generating circuit that generates a first reset pulse for resetting the trapezoidal wave generating circuit in response to the synchronizing signal and the output of the comparator; A gate pulse generation circuit outputs a gate pulse in response to the output of the comparator, a gate circuit gates a synchronization signal input in response to the gate pulse, and a trapezoidal generator is controlled by the gate pulse and the first reset pulse. A second reset pulse generation circuit is provided to generate a second reset pulse for resetting the wave generation circuit, and the trapezoidal wave generation circuit is reset not only by the first reset pulse but also by the second reset pulse. Even if the synchronization signal is lost due to dropout or the like, the gate pulse can be generated accurately.

[Conventional technology]

FIG. 4 is a block diagram of a conventional synchronization signal detection circuit. In the figure, 1 is a mono multivibrator (MMV) that outputs a pulse of a predetermined width triggered by a synchronization signal included in the input signal, and 2 is a frequency-voltage (F-V) converter that converts the frequency of the output signal into voltage. Both of them generate a voltage corresponding to the frequency of the synchronizing signal, which is input to the non-inverting input terminal of the comparator 3. 4
is a flip-flop that is set by the output of the comparator 3 and reset by the synchronizing signal, and together with a mono multivibrator 5 triggered by the output, a trapezoidal wave generating circuit 6 generates a trapezoidal wave signal whose voltage changes in a trapezoidal wave shape. It constitutes a reset pulse generation circuit that resets the The trapezoidal wave signal output from the trapezoidal wave generating circuit 6 is input to the inverting input terminal of the comparator 3 and compared with the output of the frequency-voltage converter 2. A monomultivibrator 7 serving as a gate pulse generation circuit is triggered by the output of the comparator 3 and outputs a gate pulse of a predetermined width to the gate circuit 8. The gate circuit 8 is adapted to gate the synchronization signal in response to the gate pulse.

Triggered by the falling edge of the horizontal synchronizing signal (FIG. 5a) included in the input signal, the mono multivibrator 1 outputs a pulse of a predetermined width. The frequency of this pulse is converted into a voltage by the frequency-to-voltage converter 2 (FIG. 5f), and is input to the non-inverting input terminal of the comparator 3. This voltage is comparator 3
, it is compared with the voltage of the trapezoidal wave signal output from the trapezoidal wave generating circuit 6 input to its inverting input terminal (FIG. 5g). As a result, the comparator 3 outputs a low level signal (FIG. 5b) when the trapezoidal wave signal is greater than the frequency-voltage converted signal.

Flip-flop 4, which is set by the falling edge of the output of comparator 3 and reset by the falling edge of the input horizontal synchronizing signal,
A signal (FIG. 5c) of high level during time t ₁ (low level during time t ₂ ) is output. Triggered by the falling edge of this output, the mono multivibrator 5
outputs a reset pulse (FIG. 5d) of a predetermined width. While this reset pulse is being supplied,
The trapezoidal wave generating circuit 6 discharges a charging/discharging circuit (not shown) to a predetermined fixed voltage (FIG. 5g). On the other hand, triggered by the falling edge of the output of the comparator 3, the mono-multivibrator 7 outputs a gate pulse of a predetermined width (h in FIG. 5) to the gate circuit 8. Therefore, the gate circuit 8 is closed when the gate pulse is input at the timing when the horizontal synchronizing signal (FIG. 5a) arrives, and is open during the other sections. As a result, only the horizontal synchronizing signal included in the input signal passes through the gate circuit 8 (Fig. 5i),
Noise components cannot pass through and are removed.

[Problems to be solved by the invention] By the way, since the conventional circuit is configured such that the flip-flop 4 is reset by the horizontal synchronizing signal, if the horizontal synchronizing signal is dropped due to dropout or the like (Fig. 6a), Flip-flop 4 will not be reset (FIG. 6c).
As a result, the mono-multivibrator 5 is not triggered (FIG. 6d), so the trapezoidal wave generating circuit 6 is not reset and its charging voltage rises to a predetermined fixed level (FIG. 6g). Therefore, when the horizontal synchronizing signal arrives thereafter, the flip-flop 4 is reset at its falling edge (FIG. 6c), and the mono multivibrator 5 outputs a reset pulse (FIG. 6d). As a result, the trapezoidal wave generating circuit 6 is reset, and the level of the trapezoidal wave signal is lowered.
Although the output of the comparator 3 rises (FIG. 6b), the monomultivibrator 7, which is triggered by the falling edge, is not triggered at this time and no gate pulse is generated (FIG. 6h). Therefore, the gate circuit 8 is not closed, and even though the horizontal synchronizing signal (FIG. 6a) is present, it is not output (FIG. 6i).

[Means for solving problems]

FIG. 1 is a block diagram of a synchronization signal detection circuit according to the present invention, and parts corresponding to those in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted. In the present invention, the trapezoidal wave generating circuit 6 is supplied with a reset pulse output from a reset pulse generating circuit 11 controlled by the outputs of the mono-multivibrators 5 and 7. The reset pulse generating circuit 11 includes an inverter 12 that inverts the output of the mono multivibrator 5, a NAND circuit 13 which receives the outputs of the mono multivibrators 5 and 7, and a pulse of a predetermined width triggered by the output of the NAND circuit 13. It is composed of a mono multivibrator 14 that outputs an output, and an OR circuit 15 that outputs the logical sum of the output of the inverter 12 and the output of the mono multivibrator 14 to the trapezoidal wave generating circuit 6. In the comparator 3, the output of the frequency-voltage converter 2 is supplied to its inverting input terminal, and the output of the trapezoidal wave generating circuit 6 is supplied to its non-inverting input terminal.In the flip-flop 4, the output is supplied as the set signal. The other configuration is that the output of the comparator 3 is used as the synchronization signal and the reset signal, respectively, and that the output pulse of the mono multivibrator 5 is output as a low level. This is the same as in the figure.

[Effect]

The effect will now be explained. A pulse of a predetermined width output by the mono multivibrator 1, which is triggered by a falling edge of the horizontal synchronizing signal (Fig. 2 a) included in the input signal, is converted into a voltage by the frequency-voltage converter 2, and the pulse is inverted by the comparator 3. is supplied to the input terminal (FIG. 2f). The trapezoidal wave signal output from the trapezoidal wave generating circuit 6 is supplied to the non-inverting input terminal of the comparator 3, and is compared with the signal converted into voltage by the frequency-voltage converter 2. When the signal is larger than the frequency-voltage converted signal, a high level signal is output (FIG. 2b). Flip-flop 4 is set by the falling edge of the horizontal sync signal and reset by the falling edge of the output of comparator 3 (FIG. 2c). The monomultivibrator 5 is triggered by the rising edge of the output of the flip-flop 4 and outputs a reset pulse (FIG. 2d) of a predetermined width. This reset pulse is inverted by the inverter 12 (FIG. 2j),
The signal is input to the trapezoidal wave generating circuit 6 via the OR circuit 15 (FIG. 2m). This reset pulse resets the trapezoidal wave generating circuit 6 (FIG. 2g).

On the other hand, the monomultivibrator 7 is triggered by the rising edge of the output of the comparator 3, and outputs a gate pulse of a predetermined width (h in FIG. 2) to the gate circuit 8. While this gate pulse is being supplied, the gate circuit 8 is closed and allows the horizontal synchronizing signal contained in the input signal to pass (FIG. 2i).

The gate pulse output from the mono multivibrator 7 is also input to the NAND circuit 13. The output of the NAND circuit 13, whose other input is supplied with the output of the mono multivibrator 5, will be at a low level when both inputs are at high levels, so it will fall when the output of the mono multivibrator 7 rises; It will rise when the output of the mono multivibrator 5 stops falling (Fig. 2k). Triggered by the rising edge of the output of this NAND circuit 13,
The mono-multivibrator 14 outputs a reset pulse of a predetermined width (FIG. 2l). This reset pulse is also supplied to the trapezoidal wave generating circuit 6 via the OR circuit 15. However, the width of the reset pulse output from the mono multivibrator 14 is set to be shorter than the width of the reset pulse output from the mono multivibrator 5. As a result, during normal operation, the reset pulse output from the mono multivibrator 14 is substantially masked by the reset pulse output from the mono multivibrator 5, which occurs at the same timing.

However, if the horizontal synchronizing signal is missing (FIG. 3a), the flip-flop 4 is not set (FIG. 3c). Therefore, the mono multivibrator 5 is not triggered and does not output a reset pulse.
Its output remains at a high level (Figure 3d). On the other hand, when the voltage of the trapezoidal wave signal outputted by the trapezoidal wave generating circuit 6 increases (Fig. 3g) and becomes larger than the output of the frequency-voltage converter 2 (Fig. 3f), the output of the comparator 3 changes from the low level. It is inverted to a high level (FIG. 3b), and this rising edge triggers the monomultivibrator 7 to output a gate pulse of a predetermined width (FIG. 3h). Therefore, the gate circuit 8 is closed, but since the horizontal synchronizing signal is missing, it is not output (FIG. 3i).

The gate pulse output from the mono-multivibrator 7 is also supplied to the NAND circuit 13. At this time, since a high level signal is input from the mono multivibrator 5 to the other input, the NAND circuit 13 outputs a low level signal while the gate pulse is supplied (FIG. 3k). When the output of the NAND circuit 13 rises, the mono multivibrator 14 is triggered and outputs a reset pulse of a predetermined width (FIG. 3l). Since the other input of the OR circuit 15 is at a low level, this reset pulse passes through the OR circuit 15 and is input to the trapezoidal wave generating circuit 6 (FIG. 3m). Therefore, the output of the trapezoidal wave generating circuit 6 is reset and lowered to a predetermined fixed level (FIG. 3g). As a result, when the horizontal synchronization signal arrives, it operates in the same way as in the case described above.
A gate pulse is generated.

〔effect〕

As described above, the present invention provides a synchronization signal detection circuit that includes a frequency-voltage converter that converts the frequency of an input synchronization signal into a voltage, a trapezoidal wave generation circuit that generates a signal whose voltage changes in a trapezoidal waveform, and a frequency-voltage converter. A comparator that compares the output of the trapezoidal wave generator with the output of the trapezoidal wave generating circuit, and corresponding to the synchronization signal and the output of the comparator,
A first reset pulse generation circuit generates a first reset pulse to reset the trapezoidal wave generation circuit, a gate pulse generation circuit outputs a gate pulse in response to the output of the comparator, and an input pulse in response to the gate pulse. a gate circuit that gates the synchronization signal generated by the trapezoidal wave generator, and a second gate circuit that is controlled by the gate pulse and the first reset pulse and resets the trapezoidal wave generating circuit.
A second reset pulse generation circuit is provided to generate a reset pulse, and the trapezoidal wave generation circuit is reset not only by the first reset pulse but also by the second reset pulse. Even when a signal is lost, a gate pulse can be generated accurately.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the synchronous signal detection circuit of the present invention, Figs. 2 and 3 are its timing charts, Fig. 4 is a block diagram of a conventional synchronous signal detection circuit, and Figs. 5 and 6 are its timing charts. This is a timing chart. 1, 5, 7...Mono multivibrator, 2...
...Frequency voltage converter, 3...Comparator, 4...Flip-flop, 6...Trapezoidal wave generation circuit, 8...Gate circuit, 11...Reset pulse generation circuit, 1
4...Mono multivibrator.

Claims (1)

[Scope of utility model registration request] A frequency-voltage converter that converts the frequency of an input synchronization signal into a voltage, a trapezoidal wave generation circuit that generates a signal in which the voltage changes in a trapezoidal waveform, an output of the frequency-voltage converter, and an output of the trapezoidal wave generation circuit. a first reset pulse generation circuit that generates a first reset pulse for resetting the trapezoidal wave generation circuit in response to the synchronization signal and the output of the comparator; a gate pulse generation circuit that outputs a gate pulse in response to the output; a gate circuit that gates the synchronization signal that is input in response to the gate pulse; controlled by the gate pulse and the first reset pulse; A synchronous signal detection circuit comprising: a second reset pulse generation circuit that generates a second reset pulse for resetting the trapezoidal wave generation circuit.