JP3227732B2 - Horizontal sync signal generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television (TV).
The present invention relates to a horizontal synchronization signal generator suitable for being integrated as a clock IC (semiconductor integrated circuit) for use.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing a conventional horizontal synchronizing signal generator of this kind.

A horizontal sync separation circuit 34 inputs a composite sync signal via a composite sync signal input terminal 33 and separates a horizontal sync signal from the composite sync signal. The phase detector 35 is
The phase of the horizontal synchronization signal is compared with the output of a voltage controlled oscillator (hereinafter, referred to as VCO) 36 based on the horizontal synchronization signal, and a control voltage based on the result is output to the VCO 36. The VCO 36 has its input side and output side connected to the extraction terminals 31 and 32, respectively, and oscillates at a frequency based on the control voltage given from the phase detector 35.

As described above, the conventional horizontal synchronizing signal generator constitutes a PLL (Phase Locked Loop) circuit which can always obtain an oscillation frequency synchronized with the horizontal synchronizing signal.

[0005]

However, the above-mentioned conventional horizontal synchronizing signal generator has the following problems. That is, in the conventional horizontal synchronizing signal generator, the horizontal synchronizing signal is separated from the composite synchronizing signal, and the horizontal synchronizing signal cannot be directly input. Also, it is difficult to use the VCO 36 alone. Further, when adjusting the free-running frequency of the VCO 36, it is necessary to apply a voltage from the outside to the extraction terminal 31 in a simulated manner. However, since the input terminal of the VCO 36 is connected to the phase detector 35, A deviation from the free running frequency is likely to occur, and a stable frequency may not be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and allows a horizontal synchronizing signal to be directly input as an input signal in addition to a composite synchronizing signal, and adjusts a free running frequency of a VCO with high accuracy. It is another object of the present invention to provide a horizontal synchronizing signal generator capable of performing the above operation and further using a VCO alone.

[0007]

A horizontal synchronizing signal generator according to the present invention includes a voltage controlled oscillator, a horizontal synchronizing separation circuit for inputting a composite synchronizing signal and outputting a first horizontal synchronizing signal, and a second horizontal synchronizing signal generator. A horizontal synchronization signal input terminal to which a synchronization signal is applied; and a first which selectively outputs one of the first horizontal synchronization signal and the second horizontal synchronization signal based on a first switch control signal. And a phase detector for comparing a phase of the first or second horizontal synchronizing signal output from the first switch circuit with an output of the voltage controlled oscillator and generating a control voltage based on the result of the comparison. A second switch circuit interposed between an output terminal of the phase detector and an input terminal of the voltage-controlled oscillator, the second switch circuit operating based on a second switch control signal, and a third switch control signal. Based on the said And a switch control signal generating means for generating a second switch control signal, the voltage controlled onset
Input the signal for adjusting the free running frequency of the vibrator
And a voltage control terminal .

[0008]

According to the present invention, a first switch circuit is provided before the phase detector. The first switch circuit outputs a first horizontal synchronization signal output from the horizontal synchronization separation circuit or a second horizontal synchronization signal applied to a horizontal synchronization signal input terminal based on the first switch control signal. Is selectively output. Therefore, the signal input to the horizontal synchronization signal generator according to the present invention may be a composite synchronization signal or a horizontal synchronization signal may be directly input.

Further, in the present invention, a second switch circuit that operates based on a second switch control signal is provided between the phase detector and the voltage controlled oscillator. When the second switch circuit is on, the voltage controlled oscillator oscillates at a frequency based on the output of the phase detector. Meanwhile, because this second switching circuit is in the off state the input terminal of the voltage controlled oscillator is electrically separated from the phase detector, conductive if the input signal for frequency adjustment to the voltage control terminal <br/> The free running frequency of the pressure controlled oscillator can be adjusted with high accuracy. Further, this voltage-controlled oscillator can be used alone. Further, the voltage controlled oscillator
Between the output terminal of the phase detector and the input terminal of the phase detector.
The third switch operating based on the second switch control signal.
A switch circuit, wherein the second and third switch circuits are
The phase detector and the voltage control when turned off
So that the oscillator is electrically isolated from the
Therefore, not only the voltage controlled oscillator but also the phase detector
You can use it.

[0010]

Next, an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a horizontal synchronizing signal generator according to a first embodiment of the present invention.

The horizontal sync separation circuit 21 separates a horizontal sync signal from the composite sync signal input to the input terminal 13. Between the horizontal sync separation circuit 21 and the phase detector 22,
A first circuit comprising NAND circuits 6, 7, 8 and an inverter 9
Is provided. That is, the output (hereinafter, referred to as a first horizontal synchronization signal) of the horizontal synchronization separation circuit 21 and the switch control signal X are given to the NAND circuit 8.
The NAND circuit 7 has a horizontal synchronization signal (hereinafter, referred to as a second horizontal synchronization signal) input to the horizontal synchronization signal input terminal 12.
And the switch control signal X inverted by the inverter 9
Is given. The outputs of these NAND circuits 7 and 9 are applied to NAND circuit 6, and the output of NAND circuit 6
Is supplied to the phase detection circuit 22.

Table 1 below shows the operation of the first switch circuit.

[0014]

[Table 1]

That is, the first switch circuit outputs the first horizontal synchronization signal separated from the composite synchronization signal by the horizontal synchronization separation circuit 21 based on the state value of the control signal X,
Alternatively, either one of the second horizontal synchronizing signals supplied to the terminal 12 is output to the phase detector 22.

A second switch circuit comprising two MOS transistors 4 and an inverter 5 is provided between the phase detector 22 and the VCO 23. The second switch circuit is turned on and off by the switch control signal Y.

Table 2 below shows the operation of the second switch circuit.

[0018]

[Table 2]

That is, the second switch circuit outputs the output of the phase detector 22 to VC when the control signal Y is "H".
O23, and when the control signal Y is "L", the VCO
The input terminal 23 and the output terminal of the phase detector 22 are electrically separated.

Further, a switch control signal generating circuit is constituted by the resistors 15, 16, 17, the comparators 1, 2 and the OR circuit 3. That is, the resistors 15, 16, and 17 are connected in series between the power supply and the ground, and the comparator 1
The voltage v _{2 at} the interconnection point between the resistors 15 and 16 and the voltage v _X applied to the switch control terminal 10 are input to the switch. The comparator 2 has a voltage v _{1 at} the interconnection point of the resistors 16 and 17 and a voltage v _X applied to the switch control terminal 10.
Is input. Further, the outputs of the comparators 1 and 2 are given to the OR circuit 3. Then, the output of the comparator 1 is supplied to the above-described first switch circuit as a switch control signal X, and the output of the OR circuit 3 is supplied to the above-described second switch circuit as a switch control signal Y.

In this switch control signal generation circuit, when the voltage v _X applied to the switch control terminal 10 is lower than the voltage v _{1 at} the connection point between the resistors 16 and 17 (ie,
v _X <v ₁ ; hereinafter, referred to as _VL ), and the voltage v _X is the resistance 1
(V ₁ <v _X <v) between the voltage v _{1 at} the interconnection point 6 and 17 and the voltage v _{2 at} the interconnection point between the resistors 15 and 16.
_2; hereinafter, referred to as V _M) and the voltage v _X is the resistance 15, 16
For higher than the voltage v ₂ of the interconnection point (v ₂ <v _X;
VH ), control signals are generated as shown in Table 3 below.

[0022]

[Table 3]

That is, when the voltage applied to the switch control terminal 10 is V _L , the second horizontal synchronizing signal input from the horizontal synchronizing signal input terminal 12 is applied to the phase detector 22. Further, the second switch circuit is turned on, and the output of the phase detector 22 is transmitted to the VCO 23. Therefore, this horizontal synchronizing signal generator constitutes a PLL circuit which receives the second horizontal synchronizing signal.

Further, when the voltage applied to the switch control terminal 10 is V _M, the second switch circuit is turned off, is electrically separated from the input end of the output terminal and the VCO23 of the phase detector 22 . FIG. 2 is a graph showing the control characteristics of the VCO 23 with the horizontal axis representing the control voltage and the vertical axis representing the oscillation frequency. When the voltage applied to the switch control terminal 10 is V _M, the second switch circuit for an off-state, VCO 23 oscillates in free-running frequency f _0. The control voltage v _{0 at} this time is VCO 23
This is a voltage determined by an internal circuit configuration, and is a constant value. Therefore, the free-running frequency can be adjusted with high accuracy without externally applying a control voltage.
In this state, the control voltage (v _{min to} v
_max ), the VCO 23 oscillates at a frequency corresponding to the control voltage. Therefore, in this state, the VCO
The free running frequency of the VCO 23 can be adjusted, and the VCO 23 can be used alone. In this case, the output of the VCO 23 is sent from the terminal 14 to the outside.

Further, when the voltage applied to the switch control terminal 10 is V _H , the first horizontal synchronizing signal output from the horizontal synchronizing separation circuit 21 is applied to the phase detector 22. Further, the output of the phase detector 22 is transmitted to the VCO 23 via the second switch circuit. Therefore, this horizontal synchronizing signal generator uses a PLL having a composite synchronizing signal as input.
Configure the circuit.

As described above, in this embodiment, by controlling the voltage applied to the switch control terminal 10, the PLL circuit mode in which the composite synchronizing signal is input, the horizontal synchronizing signal (second horizontal synchronizing signal) is directly transmitted. A desired mode can be selected from the input PLL circuit mode, the VCO adjustment, or the mode using the VCO alone. Further, when adjusting the VCO, the free-running frequency can be adjusted with high accuracy because the input terminal of the VCO is electrically separated from the phase detector.

FIG. 3 is a block diagram showing a horizontal synchronizing signal generator according to a second embodiment of the present invention.

The difference between this embodiment and the first embodiment is that VC
A third terminal is provided between the output terminal of O23 and the input terminal of the phase detector 22.
Since the other configuration is basically the same as that of the first embodiment, FIG.
In FIG. 1, the same components as those in FIG.

The third switch circuit is composed of two MOS transistors 18 like the second switch circuit. Then, the third switch circuit is turned on / off by the control signal Y.

In this embodiment, the phase detector 2
2, a phase detector input terminal 19 is provided at the input of the VCO 23, and a phase detector output terminal 20 is provided at the output side.

In this embodiment, the switch control terminal 1
When the voltage v _X of the voltage v ₁ below gives the 0 and the voltage v ₂
In the above case, the operation is the same as in the first embodiment. Also,
When the voltage v _X applied to the switch control terminal 10 is between voltage v ₁ and the voltage v _2, both the second and the third switching circuit is turned off, the input side and the output side phase detection of VCO23 Is electrically separated from the container 22. In this case, the VCO 23 can be used alone, and the phase detector 22 can be used alone.

[0032]

As described above, according to the present invention, the first switch circuit for switching the input of the phase detector and the second switch circuit interposed between the phase detector and the voltage controlled oscillator are provided. Since it is provided, it operates normally when any of the composite synchronizing signal and the horizontal synchronizing signal is input. Further, since the input terminal of the voltage controlled oscillator and the phase detector can be electrically separated, the free running frequency of the voltage controlled oscillator can be adjusted with high accuracy, and the voltage controlled oscillator can be used alone.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a horizontal synchronization signal generator according to a first embodiment of the present invention.

FIG. 2 is a graph showing control characteristics of a VCO.

FIG. 3 is a block diagram showing a horizontal synchronization signal generator according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a conventional horizontal synchronization signal generator.

[Explanation of symbols]

 1, 3; OR circuit 4, 18; MOS transistor 5, 9; inverter circuit 6, 7, 8; NAND circuit 10; switch control terminal 11; VCO control terminal 12; horizontal synchronization signal input terminal 13; Signal input terminal 14; output terminal 15, 16, 17; resistor 19; phase detector input terminal 20; phase detector output terminal 21, 34; horizontal sync separation circuit 22, 35; phase detector 23, 36;

Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 5/04-5/12 H04N 5/50-5/63

Claims (2)

(57) [Claims] 1. A voltage controlled oscillator, a horizontal sync separation circuit for receiving a composite sync signal and outputting a first horizontal sync signal,
A horizontal synchronization signal input terminal to which a second horizontal synchronization signal is supplied; and selectively one of the first horizontal synchronization signal and the second horizontal synchronization signal based on a first switch control signal. A first switch circuit for outputting, a phase of the first or second horizontal synchronizing signal output from the first switch circuit, and a phase of an output of the voltage controlled oscillator, and a control voltage based on a result of the comparison. A phase detector that is generated, a second switch circuit that is interposed between an output terminal of the phase detector and an input terminal of the voltage-controlled oscillator and that operates based on a second switch control signal; a switch control signal generating means for generating the first and second switch control signal based on the switch control signal, the voltage controlled onset
Input a signal for adjusting the free running frequency of the vibrator
And a voltage control terminal . 2. A have a third switch circuit which operates based on the interposed the second switch control signal between the input end of the output terminal and the phase detector of the voltage controlled oscillator,
The second and third switch circuits are turned off.
Sometimes the phase detector and the voltage controlled oscillator
The horizontal synchronization signal generator according to claim 1, wherein the horizontal synchronization signal generator is electrically separated .