JPH0720972Y2 - Integrator circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an integrator circuit using an operational amplifier, and more particularly to an integrator circuit suitable for forming a PLL circuit.

(B) Prior Art Conventionally, an integrator circuit using an operational amplifier has the configuration shown in FIGS. 3 (A) and 3 (B).

An inverting amplifier is formed by adding an input signal to the negative input terminal of the operational amplifier 1 and is composed of an input resistor R ₃ and a feedback resistor R ₄ . The resistors R ₁ and R ₂ are resistors that determine the DC potential of the input terminal IN, and are inserted between the power supplies V _cc and V _ss .

The DC voltage gain of the operational amplifier 1 is very large, and the DC voltage gain of the above inverting amplifier is determined by the ratio of the resistors R ₃ and R ₄ . The resistance R ₄ is set to a high resistance so that it is not affected by the variation in the open loop voltage gain of the operational amplifier 1.

A bias DC voltage is applied to the positive input terminal of the operational amplifier 1 by the variable resistor VR _{1 in} FIG. 3 (A). Further, in FIG. 3 (B), a fixed power source E ₀ is added.

The integrator is an operational amplifier 1, resistors R ₃ , R ₄ and capacitor C ₁
When a square wave signal is applied to the input terminal IN, the integrated triangular wave signal is output to the output terminal OUT. The lower limit frequency of the integrator is determined by the resistor R ₄ and the capacitor C ₁ , and is generally used in a frequency range of 10 times the lower limit frequency or more in order to improve the linearity of the output triangular wave signal.
Further, the output DC voltage of the integrator is determined by adjusting the variable resistor VR ₁ .

In FIG. 3 (A), the output voltage of the integrator is adjusted by applying the voltage adjusted by the variable resistor VR ₁ to the positive input terminal of the operational amplifier 1. Also, FIG. 3 (B) shows a variable resistor VR.
_The variable voltage adjusted in 1 is supplied to the negative side input terminal of the operational amplifier 1 as a current through the high resistance R ₅ , and the output voltage is adjusted.

In the output voltage adjustment, since the DC voltage gain of the operational amplifier 1 is extremely large as described above, it is required that the variable voltage of the variable resistor VR ₁ can be finely adjusted. Therefore, the variable resistor VR ₁ circuit resistance across the variable resistor VR ₁ as of FIG. 4
R ₆ and R ₇ are inserted so that the variable range of the variable resistor VR ₁ is sandwiched, the resolution of the variable voltage is increased, and fine adjustment is possible.

The adjustment by the variable resistor VR ₁ is performed so that the DC voltage of the negative side input terminal of the operational amplifier 1 set by the resistors R ₁ and R ₂ of the input circuit and the voltage of the positive side input terminal become almost the same voltage. .

In particular, the variable voltage range must be set to a range that can cover the variations in the resistors R ₁ and R _{2 and} the variations in the resistors R ₆ and R ₇ that determine the variable voltage range.

(C) Problems to be solved by the device However, in the above-mentioned output voltage adjustment of the integrator circuit, variations in resistance values of the resistors R ₁ and R ₂ of the input circuit,
When the variation of the resistance value of the resistor R _6, R ₇ which determines the voltage variable range of the variable resistor is biased in one direction, considering that it was in when the worst case, the remainder of the voltage variable range of the variable resistor挾I can't do it. That is, it is difficult to finely adjust the voltage variable, and the output voltage is very difficult to adjust because the DC voltage gain of the operational amplifier forming the integrator circuit is large.

The present invention has been made in view of the above points, and the purpose thereof is to supply a variable voltage by adjusting a variable resistor to an input terminal through a voltage follower circuit configured by an operational amplifier to output the output voltage. Adjust to eliminate the resistor that reduces the variable voltage range of the variable resistor, or
An output voltage adjusting circuit for an integrator circuit is provided which can be finely adjusted by reducing the effect of variations in resistance by reducing it.

(D) Means for Solving the Problem An integrator circuit according to the present invention is an integrator circuit in which feedback is applied to one input of an operational amplifier via a capacitor and a resistor, and a variable output voltage of the operational amplifier is adjusted. A resistor, a supply means for supplying the variable voltage of the variable resistor to the other input terminal of the operational amplifier, a voltage follower circuit having the variable voltage of the variable resistor as an input, and an output voltage of the voltage follower circuit. And a supply means for supplying the input terminal of the integrator circuit via a resistor.

Also, the integrator circuit is provided with a supply means for supplying the output voltage of the voltage follower circuit to the negative side input terminal of the operational amplifier that constitutes the integrator circuit via a resistor.

(E) Action A variable voltage set by the variable resistor is applied to the plus side input terminal of the operational amplifier and simultaneously input to the voltage follower circuit formed by the operational amplifier. The output voltage of this voltage follower circuit is supplied to the input terminal of the integrator circuit via the resistor R ₅ .

In the input voltage (DC voltage) of the integrator circuit, the voltage difference between the DC input voltage set by the resistors R ₁ and R ₂ and the variable voltage is divided by the equivalent resistance r of the input and the resistor R ₅ , and the variable voltage This divided voltage is input with reference to. This divided input voltage can be reduced by the ratio of the equivalent resistance r of the input and the value of the resistor R ₅ .

That is, the variation of the DC voltage varied by the resistors R ₁ and R ₂ can be adjusted even if the variable range of the variable voltage is increased.
The output voltage of the integrator circuit can be easily adjusted.

(F) Embodiment An embodiment of the integrator circuit according to the present invention is shown in FIG.
An explanation will be given based on (B). The same parts as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 1 (A), the variable output voltage of the variable resistor VR ₁ is supplied to the plus side input terminal of the operational amplifier 1, and at the same time, it is also supplied to the input terminal of the operational amplifier 2 forming a voltage follower circuit. As for the output voltage of this voltage follower circuit, the DC voltage gain of the operational amplifier 2 is very large.
It is almost equal to the input voltage of the voltage follower circuit.

The output voltage of the voltage follower is connected to the input terminal IN of the integrator circuit via the resistor R ₅ . This resistance R ₅ cannot be made small because it lowers the input impedance of the integrator circuit. The input resistance of the integrator circuit (including the resistor R ₅ ) must be determined so that the preceding circuit that drives the integrator circuit, for example, the phase comparator circuit (when the PLL circuit is formed) can be sufficiently driven. .

FIG. 1B shows an operational amplifier 1 in which the output voltage of the voltage follower circuit constitutes an integrator circuit via a resistor R _5.
Is connected to the negative input terminal of. This resistor R ₅ operates as an adder to the operational amplifier 1 and has a higher resistance than the feedback resistor R ₄ .

FIGS. 2A and 2B show equivalent circuits of the integrator circuits of FIGS. 1A and 1B.

In the equivalent circuit of FIG. 2 (A), E ₁ is the input resistance R ₁ , R ₂
Is the input DC voltage produced by. Further, the resistance r is an equivalent resistance generated at the input terminal when there is no input signal,
It is a parallel resistance of the resistors R ₁ and R ₂ .

The variable voltage E ₂ is an equivalent voltage produced by the variable resistor VR ₁ for adjusting the output voltage of the integrator circuit.
This variable voltage E ₂ is connected to the input terminal by a resistor R ₅ , and is applied in parallel with the input voltage E ₁ .

The variable voltage E ₂ is applied to the plus side input terminal of the operational amplifier 1, and the DC voltage gain of the operational amplifier 1 is very large as described above, so that the variable voltage E ₂ is adjusted to be almost equal to the input voltage E ₁ .

This adjustment is performed by adjusting the variable voltage E ₁ caused by the variation of the input voltage E ₁ caused by the variation of the input resistances R ₁ and R _{2 and} the variation of the resistors R ₆ and R ₇ at both ends of the variable resistor VR ₁ shown in FIG.
_It is necessary to have a variable voltage range that can be adjusted by sufficiently covering the variation of ₂ .

The input resistor R ₃ of the integrator circuit using the operational amplifier 1 has a voltage difference between the input voltage E ₁ and the variable voltage E _{2 as} shown in the equivalent circuit of FIG. Divided by ₅ and added. That is, the variable voltage E ₂ and the voltage E _i obtained by dividing the input voltage E _{1 based} on the variable voltage E ₂ are input to the integrator circuit. This divided voltage E _i is Becomes

Variable voltage supplied to the positive input terminal of operational amplifier 1
The difference between E ₂ and the divided voltage E _i can be reduced by appropriately selecting the ratio of equivalent resistance r and resistance R ₅ .

Now, under the condition of r >> R _5, the equation (1) becomes E _i ≈E ₂ (2). That is, the variable voltage E ₂ is the input resistance R _{3 of the} integrator circuit.
Is almost the same as the voltage applied to. However, since the resistance R ₅ affects the input impedance and cannot be made too small as described above, the variable voltage E ₂ must be adjusted to adjust the output voltage of the integrator circuit. The variable voltage E ₂ is {rE ₂ / (r−
The variable range is reduced by R ₅ )}.

Therefore, the adjustment of the variable voltage E ₂ is easier and finer than the adjustment of the circuit of the conventional example (FIG. 3).

The equivalent circuit of FIG. 2 (B) is an equivalent circuit of the integrating circuit of FIG. 1 (B).

The variable voltage E ₂ is applied to the negative input terminal of the operational amplifier 1 via the resistor R ₅ , and the operational amplifier 1 operates as an adder, and the current flowing through the equivalent resistance r and the input resistance R ₃ is the resistance.
It is the sum of R ₅ and the current flowing through the resistor R ₄ .

That is, the current flowing through the resistor R ₄ is obtained by subtracting the current flowing through the resistor R ₅ from the current flowing through the equivalent resistor r and the input resistor R ₃ , so that the equivalent resistance r is reduced so as to reduce the current flowing through the resistor R _4. Or resistance R ₅ can be selected.

By reducing the current flowing through the resistor R _{4 in} this way, the output voltage of the integrator circuit can be easily adjusted.

In addition, the resistance R ₅ should be selected as a high resistance. When the resistance R ₅ becomes a small value, the current flowing through the resistance R ₅ becomes the sum of the current flowing through the equivalent resistance r and the input resistance R ₃ and the current flowing through the resistance R _4, and the current flowing through the resistance R ₄ can be reduced. Therefore, the output voltage of the integrator circuit cannot be adjusted.

Adjustment of the DC output voltage of the integrator circuit (output voltage when there is no input signal to the input terminal), the first view (A), by implementing a circuit configuration of (B), the variable resistor VR ₁ Fine adjustment can be sufficiently performed without reducing the variable range and increasing the resolution of the variable voltage.

(G) Effect of the device The integrator circuit according to the present invention adjusts the output voltage by
There is an effect that the adjustment range enlarged in consideration of the variation of each resistance value is set to the variable range of the variable resistor and the fine adjustment can be sufficiently performed. That is, the output voltage can be sufficiently finely adjusted without using a high-precision resistor to reduce the above variation.

In particular, when configuring a PLL circuit in combination with a phase comparator with a tri-state output, the output signal of which is H (V _CC ), L (V _SS ) and high impedance (OFF), the output voltage of the integrator circuit Is extremely effective when adjusting the.

In addition, it has excellent features such as a simple structure and a low cost, which makes it easy to implement.

[Brief description of drawings]

1 (A) and (B) and FIGS. 2 (A) and (B) show an embodiment of an integrator circuit according to the present invention.
2B is a circuit diagram, and FIGS. 2A and 2B are equivalent circuit diagrams of FIGS. 1A and 1B. 3 (A) and 3 (B) are conventional circuit diagrams, and FIG. 4 is a variable resistor circuit diagram for setting a variable voltage range. Explanation of main numbers and symbols 1,2 …… Amplifier VR ₁ …… Variable resistor

Claims (2)

[Scope of utility model registration request] 1. A variable resistor for adjusting a DC output voltage of an operational amplifier in an integrator circuit in which feedback is provided to one input of an operational amplifier via a capacitor and a resistor, and a variable voltage of the variable resistor is calculated. Supply means for supplying to the other input terminal of the amplifier, a voltage follower circuit which receives the variable voltage of the variable resistor as an input, and an output voltage of the voltage follower circuit to the input terminal of the integrator circuit via a resistor. An integrator circuit comprising a supply means. 2. The integrator circuit according to claim 1, further comprising a supply means for supplying the output voltage of the voltage follower circuit to a negative side input terminal of an operational amplifier constituting the integrator circuit via a resistor. .