JPH0135533B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an operational amplifier that is an impedance converter with high input and low output impedance and whose purpose is to match input and output with high precision.

FIG. 1 is a schematic diagram of a conventional single-stage voltage follower type operational amplifier.

P ₁ is the input terminal, A ₀ is the amplifier, P ₃ is the output terminal, +E ₀ ,
−E ₀ is the DC power supply, G ₀ is the ground potential, and Zl is the load.

This is well known as an impedance converter with high input impedance and low output impedance.

However, due to the performance constraints of the amplifier, the circuit system shown in Figure 1 only exhibits good characteristics in the low frequency range of the commercial frequency band, and as the frequency range increases, the phase difference between input and output becomes even worse. As the impedance becomes larger and the gain of the circuit decreases, especially when the impedance of the load Zl becomes low, the good function as an impedance converter is increasingly lost.

The present invention has been made in view of these drawbacks, and an object of the present invention is to provide a voltage follower type operational amplifier with excellent frequency characteristics and load characteristics.

FIG. 2 is a block diagram of one embodiment of the present invention.

It consists of two operational amplifiers, each with a separate power supply.

_A1 is the main amplifier, and the ground potential of the power supply of the main amplifier _A1 is _G1 .

_A2 is an amplifier used for auxiliary purposes, and _G2 is the ground potential of the auxiliary amplifier _A2 .

e ₁ is the input voltage, e ₃ is the output voltage, and Δe is the potential difference between terminal P ₂ and terminal P ₃ , which is the residual deviation voltage of the main amplifier A ₁ .

+E ₁ , -E ₁ and +E ₂ , -E ₂ are DC power supplies for the main amplifier A ₁ and the auxiliary amplifier A ₂ .

Here, since the main amplifier A ₁ does not have sufficient performance, the ground potential G ₂ of the auxiliary amplifier A ₂ is the same, and there is a Δe between the input terminal P ₂ and the output terminal P ₃ of the main amplifier A ₁ . If a potential difference occurs, this difference voltage Δe can be calculated by setting the input terminal P ₂ of the main amplifier A ₁ to the ground potential G ₂ and using a DC power supply separately from the main amplifier A ₁ , so that the circuit operation is independent of the main amplifier A ₁ . The P ₁ to _{P 2 terminals} (P ₁ to G ₂
(terminals) in a closed loop. However,
When actually assembling and configuring the device, equivalently
Since the P ₁ to _{G 2} terminals are connected with a certain level of impedance, it is convenient for understanding the present invention to actively connect a certain amount of resistance between the P ₁ to _{G 2} terminals.

As a result, the potential of the _P2 terminal becomes lower than the potential of the _P1 terminal by the potential difference Δe, so the output terminal
A voltage appears at P ₃ that matches the input terminal P ₁ in magnitude and phase difference with very high precision.

The present invention is characterized in that a two-stage voltage follower is constructed by using two operational amplifiers each having an independent DC power supply and having completely independent circuits.

That is, the gist of the present invention is as follows.

The output terminal of the auxiliary amplifier A ₂ is the first input terminal P ₁ of this two-power supply two-stage voltage follower type operational amplifier.
and the negative input terminal of auxiliary amplifier A ₂ , and the positive input terminal of auxiliary amplifier A ₂ is connected to the first output terminal P ₃ of this dual-supply two-stage voltage follower operational amplifier, and its ground point G The positive input terminal of the main amplifier A ₁ is connected to the ground point G ₂ , and the positive input terminal of the main amplifier _{A 1 is} connected to _the ground point G _{2 .} The input terminal is the first output terminal of this two-power supply two-stage voltage follower type operational amplifier.
A main amplifier A ₁ connected to P ₃ and provided with a first DC power supply +E ₁ , -E ₁ between it and the ground point G ₁ , and a first output of this two-power supply two-stage voltage follower operational amplifier. It has a terminal _P3 and a load Zl connected to the second output terminal.

And these main amplifier A ₁ and auxiliary amplifier A ₂
In the operating state, the impedance seen from the first input terminal P ₁ of this two-power supply two-stage voltage follower operational amplifier and the ground point G ₂ of auxiliary amplifier A ₂ in the direction of auxiliary amplifier A ₂ is zero; The impedance seen in the opposite direction is infinite, and the AC residual deviation voltage that is insufficiently compensated in the main amplifier _A1 is input to the auxiliary amplifier _A2 , and this is input to the main amplifier A2.
It is fed back to the input of _A1 to compensate for the AC residual deviation voltage of the main amplifier _A1 .

That is, the AC residual deviation voltage Δe that is insufficiently compensated in one main amplifier A ₁ is input to the other auxiliary amplifier A ₂ , and is fed back to the input e ₁ of the main amplifier A ₁ to eliminate the residual AC voltage Δe of the main amplifier A ₁ . This is a dual power source +E ₁ , -E ₁ , +E ₂ , -E ₂ two-stage voltage follower type A ₁ , A ₂ operational amplifier for AC voltage amplification that compensates for deviation voltage Δe. As a result, the input e ₁ (voltage 1,
(assuming a phase angle of 0), the magnitude of the output e ₃ , the phase difference, and the load characteristics are improved to a much lower impedance load region than in a conventional single-stage voltage follower amplifier.

FIG. 4 shows measured values with specifications in one embodiment of the present invention.

e ₁ = between the first input terminal P ₁ and the second input terminal
When 1V (volt) is applied and the closed loop gain of main amplifier A ₁ and auxiliary amplifier A ₂ is approximately 1000, Δe ₁ = 0.001V Δe ₂ = 0.000001V ≒ 0 Δe ₃ = 0.001000V e ₂ = e ₁ + Δe ₃ = 1.001000V e ₃ = e ₁ + Δe ₂ = 1.000000 + 0.000001 = 1.000000V and e ₃ = e ₁ + Δe ₃ −Δe ₁ ≒1.000000+0.001 −0.001 ≒1.000000V, and impedance conversion has been performed. .

In particular, a remarkable improvement is seen in the phase characteristics.

Furthermore, the frequency range used can also be improved to a higher range than the conventional one.

In addition, the two amplifiers used here do not need to have individually excellent gain and phase characteristics, and in particular, the auxiliary amplifier A ₂ compensates for the residual deviation voltage of the main amplifier A ₁ . The auxiliary amplifier A ₂ only needs to have the performance of the load Zl
It has the advantage that almost no power supply capacity is required, regardless of the size of the power supply.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a conventional single-stage voltage follower type operational amplifier, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. Characteristic comparison explanatory diagram of staged voltage follower type operational amplifier, No. 4
The figure is a diagram showing measured values in one embodiment of the present invention. A ₀ ... Amplifier, A ₁ ... Main amplifier, A ₂ ... Auxiliary amplifier, +E ₀ , -E ₀ ... DC power supply of amplifier A ₀ , +
E ₂ , −E ₂ ... DC power supply of auxiliary amplifier A ₂ , e ₁ ... Input voltage, Δe ... Residual deviation voltage of main amplifier A ₁ (P ₁
~ _P2 potential difference), e ₂ ...e ₁ −Δe, e ₃ ...output voltage,
G ₁ ... Ground potential of the power supply of main amplifier A ₁ , G ₂ ... Ground potential of power supply of auxiliary amplifier A ₂ , P ₁ ... Input terminal,
P ₂ ... Input terminal of main amplifier A ₁ , P ₃ ... Output terminal,
Zl...Load.

Claims (1)

[Claims] 1. Its output terminal is connected to the first input terminal and its negative input terminal of this two-power supply two-stage voltage follower type operational amplifier, and its positive input terminal is connected to this two-power supply two-stage voltage follower type operational amplifier. an auxiliary operational amplifier connected to the first output terminal of the auxiliary operational amplifier and having a second DC power supply between it and the ground point; The negative input terminal is connected to the first output terminal of this two-power supply two-stage voltage follower type operational amplifier, and its output terminal is the first output terminal of this two-power supply two-stage voltage follower type operational amplifier. a main operational amplifier with a first DC power supply provided between the main operational amplifier, and a second input terminal and a second output of the two-power supply two-stage voltage follower operational amplifier, each commonly connected to the ground point of the main operational amplifier. terminal, and a load connected between the first and second output terminals of the two-power supply two-stage voltage follower operational amplifier, and when the main operational amplifier and the auxiliary operational amplifier are in operation, the two-power supply two-stage voltage follower operational amplifier The impedance viewed from the first input terminal of the voltage follower type operational amplifier and the ground point of the auxiliary operational amplifier toward the auxiliary operational amplifier is zero, and the impedance viewed from the opposite direction is infinite. An AC voltage characterized in that an AC residual deviation voltage that is insufficiently compensated by the operational amplifier is input to an auxiliary operational amplifier, and this is fed back to the input of the main operational amplifier to compensate for the AC residual deviation voltage of the main operational amplifier. A two-power, two-stage voltage follower type operational amplifier for amplification.