JP3461115B2 - Ramp wave control circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ramp wave control circuit, and more particularly to a control circuit of a ramp wave generation circuit for controlling a scanning signal of a CRT or the like used in a television receiver or a display device of a computer.

[0002]

2. Description of the Related Art A ramp signal is used as a vertical deflection signal of a television receiver or a display device of a computer and has a waveform shown in FIG. As the voltage of the lamp signal rises from the base voltage, the electron irradiation position is scanned, for example, from top to bottom, and when it reaches a predetermined voltage, it falls to the base voltage again, and the irradiation position also returns to the base position. Therefore, when the magnitude of the ramp wave changes, the size of the screen changes. Therefore, in order to keep the size of the screen constant, it is necessary to keep the peak value (peak / peak) of the ramp signal constant.

An AGC (Auto Gain Control) circuit is used as a circuit for keeping the ramp signal constant, and the circuit shown in FIG. 4 is conceivable, for example. The ramp wave generation circuit 51 is a circuit that creates a ramp signal, outputs the ramp signal to an image display device (not shown), and outputs the ramp signal at a predetermined timing.
The voltage of the ramp signal at t (hereinafter referred to as the sample voltage) is measured and output. The sample voltage is the comparison circuit 52.
Is input to one of the input terminals. The comparison circuit 52 is a circuit that outputs according to the difference between the two voltage inputs, and as shown in FIG. 4, a combination of a differential amplifier circuit 52a connected to the power supply voltage (Vcc) and a current mirror circuit 52b. It is a composition. A constant current I ₀ is supplied to the comparison circuit 52 from an operating current source connected to the power supply voltage Vcc. The reference voltage of the ramp signal at the predetermined timing is input to the other input terminal of the comparison circuit 52. When the sample voltage and the reference voltage are equal, the two transistors 5 of the differential amplifier 2a are
Since an equal voltage is applied to the base electrodes of 2a ′ and 52a ″, an equal current is applied to transistors 52a ′ and 52a ″.
/ 2 ・ I ₀ flows. The current mirror circuit 52b is a circuit in which equal currents flow in the two transistors 52b 'and 52b''. Therefore, when the sample voltage is equal to the reference voltage, the output current from the comparison circuit 52 does not occur. If there is a difference between the sample voltage and the reference voltage, the transistor 52
a'and 52a '' have different currents (eg 52a 'has 1/2 · I ₀ + △
I flows and 1/2 · I ₀ −ΔI flows to 52a ″).
(At this time, the total of the currents flowing through the transistors 52a ′ and 52a ″ is I _0. ) The same current flows through the two transistors 52b ′ and 52b ″ of the current mirror circuit 52b (for example, in the above example). In case of 52b 'and 52b''1/2
・ I ₀ -ΔI flows), so transistors 52a 'and 52b'
The current difference (for example, 2ΔI in the above example) cannot flow to the current mirror circuit 52b and becomes the output of the comparison circuit 52. The output of the comparison circuit 52 is connected to the first capacitor 53 connected to the power supply voltage, the second capacitor 54 grounded, and the ramp wave generation circuit 51. The output current of the comparison circuit 52 flows into the first and second capacitors 53 and 54, electric charges are accumulated, and the potential becomes according to the output of the comparison circuit 52. This potential becomes the control voltage of the ramp wave generation circuit 51, and changes the magnitude of the ramp signal after the next cycle. The output of the comparison circuit 52 is
It is output every cycle while the sample voltage and the reference voltage are equal, and the peak value of the ramp wave is kept constant.

[0004]

In the conventional AGC circuit, the constant current I ₀ supplied from the operating current source is distributed to the operational amplifier 52a, so that the capacitor 53 and the capacitor 5 are distributed.
Since the potential of No. 4 is adjusted, the maximum potential difference that the conventional AGC circuit can adjust at one time depends on the magnitude of the constant current I ₀ . In the conventional AGC circuit, when the difference between the sample voltage and the reference voltage becomes larger than a certain value, it cannot be adjusted in one cycle. In other words, when I ₀ is small, the time until the ramp signal becomes the reference waveform, that is, the so-called pull-in time, is long.

[0005] To address this, by setting a large constant current I ₀ would be to easily conceivable, increasing the constant current I _0, too sensitive output of the comparator circuit, also, Since it becomes weak against noise, distortion of the ramp waveform occurs as a result of adjusting the peak value. Therefore,
Setting a large constant current I ₀ cannot be adopted.

Further, the conventional AGC circuit uses the capacitor 5 in order to minimize the pull-in time with a small I _0.
3 and a capacitor 54 are provided. This is because the reference voltage of the ramp wave is close to 1/2 and 1/2 Vcc of the power supply voltage. Therefore, by providing the capacitor 53 connected to the power supply voltage Vcc and the grounded capacitor 54, the reference voltage is set when the power is turned on. It is provided to input 1/2 Vcc to the AGC circuit. Therefore, these two capacitors 53 and 54 are
If the pull-in time is short enough, there is no functional problem with either one. In other words, since the pull-in time is long, two capacitors are needed, which leads to an increase in cost.

In view of the above problems, the present invention has a constant current I _0.
The purpose is to increase the size only when necessary to shorten the pull-in time and thus reduce the cost of the AGC circuit.

[0008]

According to the present invention, a second comparison circuit for inputting to the first comparison circuit is provided, and the first comparison circuit is provided only when the difference between the sample voltage and the reference voltage exceeds a certain value. By increasing the adjustment function of, the pulling ability is temporarily increased.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a conceptual diagram of one embodiment of the present invention. The ramp wave generation circuit 1 generates a ramp wave by varying the magnitude of the ramp wave according to the voltage stored in the control voltage capacitor 2 and outputs the ramp wave to an image display device (not shown). Further, the ramp wave generation circuit 1 measures the voltage of the ramp wave of the output ramp wave at a predetermined timing, and inputs it to the first input terminal of the first comparison circuit 3 as a sample voltage. The reference voltage of the sample voltage is input to the other input terminal of the first comparison circuit 3, and the first comparison circuit 3 responds to the difference between the sample voltage and the reference voltage with the constant current I ₀ as the maximum value. The output current is stored in the capacitor 2 and the magnitude of the ramp wave output from the ramp wave generation circuit 1 changes. The above is the same as the conventional technique.

The sample voltage and the reference voltage are also input to the input terminal of the second comparison circuit 4. Second comparison circuit 4
When the difference between the sample voltage and the reference voltage is larger than a predetermined reference, the constant current I ₀ 'is maximum and outputs the current having the magnitude of the difference to the gate circuit 5. The gate circuit 5 opens the gate according to the magnitude of the output of the second comparison circuit 4,
The current I ₂ flows through the first comparison circuit 3. As a result, the maximum value of the output current of the first comparison circuit becomes the sum of the constant current I ₀ and the current I _2, and the amount of current accumulated in the capacitor 2 at one time increases, so that the control of the ramp wave control circuit is increased. Ability is temporarily improved.

Next, a specific circuit example of the embodiment of the present invention will be described. FIG. 2 shows a circuit diagram of an embodiment of the present invention. The areas indicated by the dashed thin line rectangles are areas corresponding to the first comparison circuit 3, the second comparison circuit 4, and the gate circuit 5 in FIG. 1, respectively.

Since the structure of the first comparison circuit 3 is similar to that of the conventional technique, its detailed description will be omitted.

The second comparison circuit 4 is supplied with a constant current I ₀ 'and is composed of a differential amplifier and two constant current sources 4a. Similar to the first comparison circuit 3, a total current I ₀ ′ flows through the two transistors of the differential amplifier according to the difference between the sample voltage and the reference voltage. By the way, the two constant current sources form a current mirror circuit (not shown),
While it works to flow I ₁ , no current larger than the constant current I ₁ flows. If the difference between the reference voltage and the sample voltage is within the predetermined range, the currents flowing through the two transistors of the operational amplifier are balanced and enter within the predetermined range, and the magnitude of the current flowing through one transistor is smaller than I _1. Therefore, there is no output from the second comparison circuit 4. Then, when the difference between the sample voltage and the reference voltage becomes larger than a predetermined value and the current flowing in one of the transistors of the differential amplifier exceeds I ₁ , the current that cannot flow in the constant current source is output as the output of the second comparison circuit. It is input to the gate circuit 5.

The gate circuit 5 is composed of two transistors 5a whose emitters are grounded, and a current mirror circuit 5b. The input of the gate circuit 5 is connected to the base electrodes of the two transistors, one transistor of the current mirror circuit is connected to two grounded transistors, and the other transistor of the current mirror circuit 5b is the current mirror circuit. It is the output of the circuit 5. Second comparison circuit 4
Output, the one of the two grounded transistors 5a of the gate circuit 5 is turned on. Then,
Current mirror circuit 5 connected to these two transistors
Since a current flows in b, the gate circuit 5 outputs the current I ₂ .

Since the output from the gate circuit 5 is connected to the first comparison circuit 3, the maximum value of the output of the first comparison circuit is the sum of the constant current I ₀ and the output I ₂ of the gate circuit 5. Become.

Therefore, the ramp wave control circuit of this embodiment can increase the maximum value of the output of the comparison circuit 3 only when the difference between the sample voltage and the reference voltage exceeds a predetermined magnitude.

[0017]

According to the present invention, since the pull-in capability can be increased only when necessary by the second comparison circuit, the pull-in time of the ramp wave generating circuit when the power is turned on can be shortened.

Further, in order to shorten the pull-in time, the capacitors 53 and 5 which are respectively placed in the power supply voltage and the ground.
4 can be reduced to one capacitor 2. The AGC circuit is generally an integrated circuit (IC) and is manufactured integrally, while the capacitors 53, 54 and 2 require a large capacity to function to adjust the control power supply of the AGC circuit, and the IC It is an external component that cannot be built inside and is connected to the outside of the IC using wiring. Therefore, even if the number of the second comparison circuits is increased, the manufacturing cost of the IC hardly changes, but it is possible to reduce the cost by reducing the external capacitors. Therefore, the total cost of manufacturing the AGC circuit is increased. Will be reduced.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a ramp wave control circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a ramp wave control circuit according to an embodiment of the present invention.

FIG. 3 is a diagram showing a waveform of a ramp wave.

FIG. 4 is a circuit diagram of a conventional ramp wave control circuit.

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Claims (3)

(57) [Claims] 1. A ramp wave generation circuit for outputting a ramp wave and a sample voltage which is a voltage value of a ramp wave at a predetermined timing according to a control voltage, and a constant current I ₀ are supplied to the sample voltage and the sample voltage. A reference voltage, which is a reference value, is input, and a first comparison circuit that outputs a current according to a difference between the sample voltage and the reference voltage, and an output of the first comparison circuit is stored to store the ramp wave. A capacitor that changes the control voltage of the generation circuit and a constant current I ₀ 'are supplied,
A second comparator circuit that outputs the current when the sample voltage and the reference voltage are input and the difference between the sample voltage and the reference voltage exceeds a predetermined value; and an output current of the second comparator circuit. there are input, while there is the input, and a gate circuit for outputting a current I _2, the current I _2, the first
Is added to the constant current I ₀ supplied to the comparison circuit of
A ramp wave control circuit for keeping the magnitude of the ramp wave output from the ramp wave generation circuit constant by increasing the maximum value of the output current of the comparator circuit. 2. The second comparison circuit has a pair of transistors that form an operational amplifier, and a constant current source that flows a constant current I ₁ that is connected to each of the transistors and that is a constant current source. Lamp wave control circuit. 3. The gate circuit includes a transistor having a grounded emitter and a mirror circuit connected to the transistor, and an input to the gate circuit is input to a base of the transistor having a grounded emitter, and the gate is connected to the gate. The current I2 output from the circuit is output from the mirror circuit connected to the transistor, and the magnitude of the current I2 is
The ramp wave control circuit according to claim 1, wherein the ramp wave control circuit changes according to a magnitude of an input to the gate circuit.