JPS63275218A - Saw-tooth wave generation circuit - Google Patents

Abstract

PURPOSE:To stably obtain a saw-tooth wave having a constant amplitude by forming the saw-tooth wave by means of an integration circuit by switching and connecting a constant-current power supply and a variable current power supply periodically to the input of the integration circuit, and controlling its amplitude so as to be constant by means of the current value of the variable current power supply. CONSTITUTION:The saw-tooth wave which the leading inclination and the trailing inclination are determined by the respective current values of the constant current regulated power supply 5 and the variable current power supply 6 periodically switched and connected to the input of the integration circuit 4, is obtained as the output of the integration circuit 4. Then, a feedback control is performed so as to keep the amplitude of the saw-tooth wave constant, by controlling the inclination of the saw-tooth wave by changing the current value of the variable current power supply by a comparative error voltage between the output voltage of the integration circuit 4 and a reference voltage. Thus, the saw-tooth wave having the constant amplitude can be stably generated, extending over a wide frequency hand.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sawtooth wave generation circuit that generates a sawtooth wave of a predetermined amplitude. pipe (CR
It is applied to the deflection circuit of Cathode Ray Tube (T: Cathode Ray Tube), etc.

[Summary of the invention]

The present invention provides a sawtooth wave generation circuit applied to a deflection circuit of a cathode ray tube (CRT), etc., by periodically switching and connecting a constant current source and a variable current source to the input of the integrating circuit. A sawtooth wave with a predetermined period is formed as an output, and the slope of the sawtooth wave is controlled by changing the current value of the variable current source based on a comparison error voltage between the output voltage of the integrating circuit and a reference voltage. , which generates a sawtooth wave with a predetermined amplitude. .

[Conventional technology]

Traditionally, various standard television systems such as NTSC, PAL, and SECAM, as well as HDTV (High Definition
ion TV) Various television signals compatible with high-definition television systems such as so-called high vision, and image signals for computer graphics. 2. Description of the Related Art A CRT display device in which an image is displayed using a cathode ray tube (CRT) is known.

Generally, in a CRT display device, an electron gun of the CRT emits an electron beam whose brightness is modulated according to a video signal, and this electron beam is deflected by a deflection magnetic field generated by a deflection coil, so that a fluorescent screen is illuminated by the electron beam. Images are displayed by scanning (so-called rask scan). Deflection scanning of the electron beam with respect to the fluorescent screen is performed by a deflection circuit that forms a sawtooth wave synchronized with the vertical synchronization signal of the input video signal and supplies it to the vertical deflection coil, and also synchronized with the horizontal synchronization signal of the input video signal. This is done by forming a sawtooth wave and supplying it to a horizontal deflection coil. Therefore, in the CRT display device, the deflection scanning range, that is, the screen size is set by the amplitude of each sawtooth wave formed by the deflection circuit.

In addition, since images displayed on a CRT have image distortions due to the shape of the fluorescent screen, distortions in the deflection system, etc., a waveform for correcting the image distortion is formed from a sawtooth wave, and a sawtooth waveform for deflection scanning is used. The above image distortion is corrected by superimposing the image on the image. Furthermore, video projectors that project images from a high-brightness CRT onto a screen are known to cause image distortion due to the positional relationship between the CRT and the screen. In a multi-tube video projector that projects a color image onto a screen using a CRT and synthesizes a color image on the screen, the positional relationship between each CRT and the screen is different, causing optical distortion to the three primary color images projected onto the screen. Since the overlay error causes a so-called registration error, the positional relationship between each CRT and the screen is adjusted mechanically or optically, and a registration error correction waveform is formed from a sawtooth wave to correct the deflection scanning of each CRT. The registration error is corrected by superimposing it on the sawtooth wave.

In the deflection circuit in the CRT display device as described above, for example, as shown in FIG.
A sawtooth wave generation circuit configured with a Phase Locked Loop (Phase Locked Loop) circuit generates a sawtooth wave for electron beam deflection scanning and a sawtooth waveform for correcting image distortion and registration errors.

The sawtooth wave generation circuit shown in the block diagram of FIG. 4 includes a phase comparator 42 whose one input terminal is connected to a signal input terminal 41.
A low-pass filter (
A sawtooth wave generation type voltage controlled oscillator (VCO) 44 is connected to a control input terminal via an LPF 43, and the output terminal of the voltage controlled oscillator 44 is connected to a signal output terminal 45, and the phase comparison It is constituted by a PLL circuit connected to the other input terminal of the device 42.

The phase comparator 42 compares the phases of, for example, a horizontal synchronizing signal supplied as an input signal (flN) to the signal input terminal 41 and the output signal (foLIT'') of the voltage controlled oscillator 44.The phase comparator 42 The phase error output obtained in is passed through the low-pass filter 43 to remove high frequency noise components, and is then applied to the voltage controlled oscillator 4 as a control voltage.
4 control input. The voltage controlled oscillator 44 is comprised of an oscillation circuit whose oscillation frequency is variably controlled in accordance with the control voltage supplied to the control input terminal, and which generates a sawtooth wave with a constant amplitude. By performing feedback control using the obtained phase error output, the oscillation phase is fixed to the phase of the input signal (fIN), and a sawtooth wave with a constant amplitude is output at a horizontal synchronous frequency synchronized with the input signal (flN). It is output from the signal output terminal 45 as a signal (f ont ).

[Problem that the invention seeks to solve]

By the way, the conventional sawtooth wave generation circuit constructed using a PLL circuit as described above has a large number of circuit elements because it is constructed by combining a phase comparator and a voltage controlled oscillator, and is therefore unsuitable for integration into an integrated circuit. The oscillation frequency of the voltage controlled oscillator is controlled to generate a sawtooth wave of a desired frequency and the phase is fixed, so the transient response until the phase is stabilized becomes a frequency change and the deflection system changes. There is a problem that there is a possibility that the operation may be disturbed.

In particular, a single CRT can display images using various television signals compatible with various standard television systems such as NTSC, PAL, and SECAM, high-definition television systems such as HDTV, and image signals for computer graphics.
When switching the deflection frequency of a deflection system to support multi-scanning, as is done in a display device, for example, the horizontal scanning frequency in the high-definition system is about four times that of the NTSC system, and the conventional sawtooth pattern configured with the above-mentioned PLL circuit is In wave generation circuits, it is difficult to realize a circuit configuration that can stably operate PLL over a wide frequency range, and it is also difficult to realize a circuit configuration that can stably operate PLL in a wide frequency range. Problems include the occurrence of image distortion due to changes in the steady-state phase error.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, the present invention provides a sawtooth wave generation circuit with a novel configuration that can stably generate a sawtooth wave with a constant amplitude over a wide frequency band. It is something to do.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention includes an integrating circuit, a constant current source, a variable current source, and a system in which the constant current source and the variable current source are periodically switched manually by the integrating circuit. a switching circuit to be connected, and a comparison circuit to compare the output voltage of the integration circuit with a reference voltage; It is characterized by controlling the slope of the waves.

[Effect]

In the sawtooth wave generating circuit according to the present invention, the sawtooth wave whose rising slope and falling slope are determined by the respective current values of the constant current source and the variable current source which are periodically switched and connected to the input of the integrating circuit is generated by the sawtooth wave generating circuit. is obtained as the output of By controlling the slope of the sawtooth wave by changing the current value of the variable current source using the comparison error voltage between the output voltage of the integration circuit and the reference voltage, the amplitude of the sawtooth wave becomes constant. Feedback control is performed as follows.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

The embodiment shown in the block diagram of FIG. 1 is a sawtooth wave generation circuit for a registration correction waveform in a deflection circuit of a multi-scan multi-tube video projector. A sawtooth wave (f4) with a constant amplitude is formed in an integrating circuit 4 in synchronization with a synchronizing signal (f+) of a frequency suitable for various systems, and is outputted from a signal output terminal 7.

In this embodiment, the signal input terminal 1 is connected to the cell 1 input terminal of the RS flip-flop 2. The output terminal of the flip-flop 2 is connected to the control input terminal of the switching circuit 3. 1. Furthermore, the input terminal of the integrating circuit 4 is connected to the variable current source 6, and is also connected to the constant current source 5 via the switching circuit 3. Also,
The integrating circuit 4 has its output terminal connected to the signal output terminal 7, and is also connected to each non-inverting input terminal of a first and second voltage comparator circuit 8.9 each constituted by an operational amplifier. There is.

The first voltage comparator circuit 8 has its inverting input terminal connected to the reference voltage source 10, and its output terminal connected to the reset input terminal of the RS flip-flop 2. Here, the reference voltage source 10 inputs a reference potential (■,) that defines the maximum voltage of the sawtooth wave generated in the sawtooth wave generation circuit of this embodiment to the inverted input of the first voltage comparison circuit 8. I'm giving it to the edge.

Further, the second voltage comparison circuit 9 has a reference voltage source 11 connected to its inverting input terminal, and its output terminal is connected to the control input terminal of the variable current source 6 via a low-pass filter (LPF) 12. It is connected. Here, the reference voltage source 11 is 1/2 of the reference potential (VH) that defines the maximum voltage of the sawtooth wave generated in the sawtooth wave generation circuit of this embodiment.
A reference potential (VC) of VC is applied to the inverting input terminal of the second voltage comparison circuit 9.

The integrating circuit 4 includes an operational amplifier 4A, an integrating capacitor 4B connected between the output terminal and the inverting input terminal of the operational amplifier 4A, and the reference potential (■, ) is constituted by a reference voltage source 4C that provides a reference potential (VC) of 1/2 of VC.

In this embodiment, the RS flip-flop 2 is
For example, as shown in FIG. 2, a synchronizing signal (fl
), for example, is set at every predetermined rising timing (to) of the horizontal scanning period (Th) of the horizontal synchronizing signal, and is traced until it is reset at the rising timing (tl) of the comparison output from the first voltage comparator circuit 8. During the period (TIL), the logic becomes rHJ, and its output pulse (f
2) is supplied to the control input terminal of the switching circuit 3 as a control signal.

The switching circuit 3 also operates during a retrace period (T
During IIE), the constant current source 5 is connected to the input terminal of the integrating circuit 4, and the trace period (TTR) from the reset timing (tl) to the next set timing (to) is determined.
During operation, the constant current source 5 is controlled by the output pulse of the flip-flop 2 so as to be disconnected from the input terminal of the integrating circuit 4.

Further, the integrating circuit 4 has a capacitor 4B charged during the trace period (TTR) by the variable current source 6 connected to its input terminal, so that the potential at its output terminal changes from the variable current source 6 connected to the variable current source 6. The potential at the output terminal decreases to the ground potential (VL) with a falling slope determined by the current value of 6, and is discharged by the constant current source 5 connected during the retrace period (TRE). is the ground potential (VL) with a rising slope determined by the current value of the constant current source 5.
), a sawtooth wave with a repetition period synchronized with the input signal (fl) is formed.

Further, the first voltage comparison circuit 8 includes the reference voltage source 1
0 is compared with the potential at the output end of the integrating circuit 4, and the potential at the output end of the integrating circuit 4 is determined to be the reference potential (VH) given by the reference voltage source 10.
)I) A comparison output (f3) that rises at a timing (t, ) that coincides with I) is supplied as a reset pulse to the reset input terminal of the RS flip-flop 2.

Therefore, the RS flip-flop 2 is set at the rising timing (m) of the synchronizing signal (f) supplied to the signal input terminal 1, and the capacitor 4B of the integrating circuit 4 is discharged by the constant current source 5. When the potential at the output terminal rises from the ground potential (Vt) to the reference potential (VH), it is reset at the rising timing (tl) of the comparison output from the first voltage comparator 8, and from the set timing (to). During a constant trace period (T□) up to the reset timing (1+), the operation of the switching circuit 3 is controlled so that the constant current source 5 is connected to the input terminal of the integrating circuit 4.

By resetting the RS flip-flop 2 with the comparison output (rs) from the first voltage comparator 8,
The retrace period (TRE) is kept constant.

Further, the second voltage comparator 9 includes the reference voltage source 11
The reference potential (V,) given by is compared with the potential at the output end of the integrating circuit 4, and a comparison output current corresponding to the potential difference is output. The comparison output current from the second voltage comparator 9 is stored in the capacitor 13 of the low-pass filter 12, and converted into a voltage corresponding to the average potential of the sawtooth wave output from the integrating circuit 4. is supplied to the control input of source 6.

The variable current source 6 is connected to the low pass filter 1.
A charging current having a current value corresponding to the comparison output of the second voltage comparator 9 supplied via the voltage comparator 2 is supplied to the capacitor 4B of the integrating circuit 4, and during the trace period (TTll), the charging current of the integrating circuit 4 is The potential at the output end is lowered from the reference potential (■A) to the ground potential (VL).

By controlling the current value of the variable current a6 in a control loop including the second voltage comparator 9, the falling slope of the trace period (Tt++) of the sawtooth wave output from the integrating circuit 4 is As shown in (A) in Figure 3,
Control is performed so that the average potential of the sawtooth wave is stabilized to match the reference potential (VC).

That is, the sawtooth wave obtained at the output terminal of the integrating circuit 4 has a falling slope during the trace period (TTR) that changes depending on the current value of the variable current source 6, and the current value of the variable current source 6 changes. increases more than the current value of the falling slope of the sawtooth wave in the stable state of the control loop, and as the falling slope becomes larger as shown in (B) in FIG. 3, the trace period ('rti) (Tst)
Then, the potential at the output terminal of the integrating circuit 4 drops from the reference potential (■□) to the ground potential (VL), and the average potential decreases.
Conversely, when the current value decreases and the falling slope increases as shown in (C) in FIG. 3, the average potential increases, so that the reference potential (V
Due to the operation of the control loop that controls the current value of the variable current source 6 based on the comparison output with C), the falling slope during the trace period (TTll) changes to the stable state of the control loop, that is, (A ), control is performed so that the average potential of the sawtooth wave is stabilized in a state consistent with the reference potential (vc'').

In the sawtooth wave generating circuit of this embodiment, the switching circuit 3 periodically connects the constant current source 5 to the input terminal of the integrating circuit 4 in synchronization with the synchronizing signal (fl) supplied to the signal input terminal 1. By doing so, the integration circuit 4 obtains the synchronization signal (
A sawtooth wave with a predetermined period synchronized with fl) is formed, and the second voltage comparator 9 outputs the current value of the variable current source 6 for comparison between the potential of the sawtooth wave and the reference potential (VC). Since the amplitude of the sawtooth wave is controlled to be constant by feedback control, the sawtooth wave with a constant amplitude is generated in synchronization with a synchronization signal of a frequency suitable for various systems that is selectively supplied to the signal input terminal 1. can be formed by the integrating circuit 4 and output from the signal output terminal 7.

〔Effect of the invention〕

In the sawtooth wave generating circuit according to the present invention, a constant current source and a variable current source are periodically switched and connected to the input of the integrating circuit to form a sawtooth wave in the integrating circuit, and the amplitude of the sawtooth wave is determined by the variable current source. By controlling the current value of the source to be constant, it is possible to obtain a sawtooth wave with a constant amplitude at a predetermined period.
Moreover, since it does not use an oscillation circuit like the conventional PLL sawtooth wave generation circuit, it can operate stably over a wide frequency range, and the operating frequency can be adjusted without transient fluctuations in the frequency of the sawtooth wave. can be switched.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a signal waveform diagram for explaining the operation of the above embodiment, and FIG. 3 is a block diagram showing the signal output terminal of the above embodiment. FIG. 3 is a waveform diagram of a sawtooth wave. FIG. 4 is a block diagram showing the configuration of a conventional sawtooth wave generating circuit using a PLL circuit. 1... Signal input terminal 3... Switching circuit 4... Integrating circuit 5... Constant current source 6... Variable current source 7... Signal output terminal 9... Voltage comparison circuit 12...・Low pass filter

Claims (1)

[Scope of Claims] An integrating circuit, a constant current source, a variable current source, a switching circuit that periodically switches and connects the constant current source and the variable current source to the input of the integrating circuit, and the integrating circuit. and a comparison circuit for comparing the output voltage of the circuit with a reference voltage, and the output of the comparison circuit changes the current value of the variable current source to control the slope of the sawtooth wave output from the integration circuit. A sawtooth wave generation circuit characterized by: