JPS5918893B2 - Sawtooth wave generation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sawtooth wave generation circuit that generates a sawtooth wave with high speed and high precision.

A conventional circuit of this type is composed of an integrating circuit and a switching element 1, as shown in FIG.

Although a transistor or a diode is used as the switching element 1, the resistance of these elements does not become zero when they are in an on state, which causes the accuracy of the output signal to deteriorate.

In addition, in devices using transistors as switching elements, it takes a long time for the transistor to transition from an on state to an off state, which is an obstacle to increasing speed.

FIG. 2 is a diagram showing the deviation of a general sawtooth wave from the ideal waveform.

Voffset is the error voltage of the signal level during the sweep pause of the sawtooth wave.

V if the gain of the integrating amplifier A1 in FIG. 1 is sufficiently larger than 1.

ff5et is expressed by the following formula. Voffset -
-E ...[1]1 In the formula, r is the resistance value when the switching element 10 is in the on state.

Equation [1] shows that V is the OFF5e of switching element 1.
It represents that it is proportional to the resistance in the on state, and ideally it should be zero.

tl is the rise delay time of the sawtooth waveform.

This delay also becomes an error voltage of the deviation from the ideal waveform.

When a transistor is used as a switching element, the length of the transition time from the on state to the off state of the transistor determines tl.

As described above, the circuit shown in FIG. 1 requires both the operating speed of the switching element 1 and the low resistance value in the on state, but there is no one that satisfies both of these requirements, and therefore, there is no one that can satisfy both of these requirements. It was difficult to obtain precision sawtooth waves.

The object of the present invention is to eliminate these drawbacks and provide a sawtooth wave generating circuit that can be operated at high speed and with high accuracy.

FIG. 3 is a block diagram of a circuit according to the present invention.

In the figure, E, R1, A1. C1 is each element of the integrating circuit, E is an input power supply, R1 is a human resistor, A1 is an integrating amplifier, C1 is a capacitor, A2 is an error amplifier, 1 is a switching element, and R2 is an input resistance of the integrating circuit.

Since R2 is selected to have a relatively small value, it also plays the role of a protective resistor.

In the sawtooth wave generation circuit configured as described above, when the switching element 1 is on, that is, when the sawtooth wave is not being swept, the error amplifier A2 detects and amplifies the error from the ground level of the output. It is fed back to the integrating circuit through the switching element 1.

This feedback is negative feedback and works to bring the output closer to ground level.

The error voltage of the output at this time (V in Figure 2).

Corresponds to ff5et.

) Voffset can be expressed as follows.

R2+ r Voffset”□E・・・・・・[2] RIGIG2
(Rt+R2+r) In the formula, G1 is the voltage amplification factor of A1, G2 is the voltage amplification factor of A2, and r is the resistance value when the switching element 10 is in the on state.
08 can be obtained, so when the circuit specifications are selected so that the value of G1×G2 is 104 to 108, equation [2] can be expressed as follows.

I R2+r voffset-□・□E ・・・・・・[3]G1
G2R□ Comparing the above formula [1] and formula [3], Voffse
It can be seen that t is greatly improved in equation [3].

Further, even if the resistance value r when the switching element is in the on state becomes a somewhat large value, V.

Since the value of ff5et is extremely small, there is no problem at all.

When a switching element changes from an on state to an off state, a high speed switching element is required in the circuit of FIG. 3 as well.

However, as explained above, the resistance in the on state may be somewhat large, so an element that can be used at high speed, such as a diode, may be selected.

While the switching element is off, the error amplifier is disconnected from the circuit and the integrator circuit generates a sawtooth wave with a slope determined by the input voltage.

In the above explanation, the case where the application is applied to a Miller integrating circuit was described, but this invention is also applicable to a constant current type sawtooth wave generating circuit,
Needless to say, the present invention can also be applied to bootstrap type sawtooth wave generation circuits.

As explained above, by providing an error amplifier, this invention eliminates the need to consider the conditions for reducing the on-state resistance of the switching element. It is now possible to obtain highly accurate sawtooth waves.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional sawtooth wave generation circuit, FIG. 2 is a diagram showing the deviation of the sawtooth wave from an ideal waveform, and FIG. 3 is a block diagram of the sawtooth wave generation circuit of the present invention. In the figure, 1 is a switching element or a switching circuit, A1 is an integrating amplifier, A2 is an error amplifier, C1 is an integrating capacitor, E is an input voltage, and R1tR2 is an input resistance of the integrating circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1 Integrating amplifier, a switching circuit that connects or opens fm between the input terminal and output terminal of this integrating amplifier, amplifies the difference between the voltage of the output terminal and the reference voltage, and connects the negative voltage to the input terminal via the switching circuit. A sawtooth wave generation circuit characterized by having a feedback error amplifier.