JPH07105671B2 - Balanced amplifier - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a closed loop balanced amplifier, and more particularly to a bias method thereof.

[Conventional technology]

FIG. 3 shows an example of a bias method in a closed loop circuit of a conventional balanced amplifier, in which a balanced output is obtained by biasing a feedback resistor with an unbalanced current source I ₀ . That is,
A resistor R ₁ is connected between the negative input terminal − and the normal output terminal 3 of an operational amplifier A ₁ having positive and negative input terminals and normal and inverted output terminals, and a current source 5 is connected to the positive input terminal +. Connect. In addition, there is a resistor between the positive input terminal + and the inverting output terminal 4.
Connect R ₂ . A positive power supply terminal 1 and a negative power supply terminal 2 are connected to the power supply terminals of the operational amplifier A ₁ , respectively.

Here, the current value of the current source 5 is I₀And the forward output terminal voltage
V_OUT, Inverting output terminal voltage V ▲ ▼ And unbalanced current I₀Are converted to balanced outputs.

[Problems to be solved by the invention]

In the circuit configuration of a conventional balanced amplifier we described above, positive and negative input terminals + and - of the voltage becomes equal to the voltage at the inverting output terminal 4, only the same as the voltage range of the output terminal of the operational amplifier A ₁ of the operational amplifier A ₁ It is necessary to have a circuit configuration that allows a wide voltage range of the input terminals + and-. The operational amplifier A ₁ input terminal +, - voltage greatly changes by the above reasons, there is a drawback that error is increased due to common-mode rejection ratio (CMRR) characteristic of the operational amplifier A _1. Further, the large change in the input withstand power is not only susceptible to an error due to the output impedance of the current source, but also has a drawback that it is necessary to widen the output dynamic range of the current source.

[Means for solving problems]

It is an object of the present invention to provide a balanced amplifier including a bias circuit that reduces the amount of change in the input terminal voltage and improves the accuracy of converting an unbalanced current into a balanced output.

The balanced amplifier of the present invention includes an operational amplifier, a first resistor connected between the negative input terminal and the non-inverting output terminal of the operational amplifier, and a positive resistance connected between the positive input terminal and the inverting output terminal of the operational amplifier. A second resistor, a third resistor whose one end is connected to the negative input terminal of the operational amplifier, a fourth resistor whose one end is connected to the positive input terminal of the operational amplifier, and a normal resistor of the operational amplifier. , Or a current source connected to the negative input terminal, and the other ends of the third and fourth resistors are interconnected and connected to a reference voltage.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of a balanced amplifier according to an embodiment of the present invention. In this embodiment, a feedback resistor R ₁ is connected between the negative input terminal and the non-inverted output terminal 3, and a feedback resistor R ₂ is connected between the positive input terminal + and the inverting output terminal 4. And the negative input terminal −
Between the positive input terminal + and the reference voltage V _ref, and resistors R ₃ and R _{4 respectively.}
And the current source 5 is connected between the negative input terminal-and the negative power supply terminal. The input signal is given as the output of the current source 5.

Next, the operation of this embodiment will be described. Now each resistance R₁~ R_Four
The resistance value of R₁~ R_FourAnd R₁= R₂= R_f, R₃= R_Four= R_sage,
Reference voltage V_refIs 0V and the current value of the current source 5 is I₀And
Then, the voltage of the normal output terminal 3 is changed to V_OUTOf the inverted output terminal 4
Voltage is V ▲ ▼, and forward of imaginary short
Invert the input voltage to V₁AndResistance R_FourThe current flowing through I_FourAndResistance R₂The current flowing through I₂AndSet the current value of the current source 5 to I₀Then I₀= I₂＋ I_Four (6) Also, output V of the forward / reverse output terminals 3 and 4_OUTAnd V ▲ ▼
Is a balanced outputFrom equations (4), (5), and (6)From equations (3) and (8)From equations (7) and (9) And output V_OUT, V ▲ ▼ is the resistance value R_s, I.e.
Anti-R₃And R_FourIt becomes irrelevant to the resistance value of_sIs in and out
It does not affect the force relation in the formula. Also, here is equation (3)?
As can be seen, the input voltage ratio is R_s/ (R_s+ R
_f) And the resistance R₃, R_FourResistance value R_SResistance R₁, R₂Resistance value R
_fThe smaller the input voltage deviation, the smaller
Become

FIG. 2 is a circuit diagram of a balanced amplifier according to another embodiment of the present invention.

In this embodiment, the position of the current source 5 in the embodiment of FIG. 1 is changed, and this constant current source 5'is connected to the positive power supply terminal 1
It has put between - the negative input terminal of the operational amplifier A ₁ and. The principle of operation is the same as in the embodiment of FIG.

The embodiment shown in FIG. 2 has an advantage that it can be applied to the case where the current source for control is of a bare type.

[Effects of the Invention] As described above, according to the present invention, the fluctuation of the input terminal potential of the balanced amplifier can be reduced by adding two resistors, and the common-mode input voltage range of the balanced amplifier can be reduced. Not only is this done, but as a result, the error due to the CMRR characteristics of this balanced amplifier can be reduced. In addition, the output dynamic range of the current source connected to the input terminal of the balanced amplifier can be small, and the error due to the internal equivalent resistance (output impedance) of the current source can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of another embodiment of the present invention, and FIG. 3 is a bias circuit diagram of a conventional balanced amplifier. 1 ...... positive power supply terminal, 2 ...... negative power supply terminal, 3 ...... noninverting output terminal, 4 ...... inverting output terminal, A ₁ ...... balanced amplifier, I ₀ ...... controlled current source, V _ref ...... reference voltage Source, R _{1 to} R ₄ ... Resistance, 5,5 ′
...... Current source.

Claims (1)

[Claims] 1. An amplifier having positive and negative input terminals and non-inverted and inverted output terminals; a first resistor connected between the negative input terminal and the non-inverted output terminal of the amplifier; A second resistor connected between the positive input terminal and the inverting output terminal of the amplifier, a third resistor having one end connected to the negative input terminal of the amplifier, and one end of the positive resistor of the amplifier. A fourth resistor connected to the input terminal, a current source connected to the non-inverting or inverting input terminal of the amplifier, and the other ends of the third and fourth resistors are interconnected to provide a reference voltage. Means for inputting a current from the current source to the input terminal and outputting a voltage from the non-inverting and inverting output terminals of the amplifier.