OUT

OUT

cm

REF

V

V

1

V

V

2

2

+

-

+

æ

ö

=

=

ç

÷

è

ø

2

4

2

D IF F

O U T

O U T

IN

R E F

1

3

4

1

R

R

R

V

V

V

V

1

V

1

R

R

R

R

+

-

æ

ö

æ

ö

æ

ö

=

-

=

´

+

-

´

+

ç

÷

ç

÷

ç

÷

+

è

ø

è

ø

è

ø

4

2

2

out

ref

in

3

4

1

1

R

R

R

V

V

1

V

R

R

R

R

-

æ

ö æ

ö

=

´

´

+

-

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ç

÷ ç

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+

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ø

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NE5532, NE5532A, SA5532, SA5532A

www.ti.com

SLOS075J – NOVEMBER 1979 – REVISED JANUARY 2015

Typical Application (continued)

9.1.2 Detailed Design Procedure

The circuit in Figure 4 takes a single-ended input signal, VIN, and generates two output signals, VOUT+ and VOUT–

using two amplifiers and a reference voltage, VREF. VOUT+ is the output of the first amplifier and is a buffered

version of the input signal, VIN Equation 1. VOUT– is the output of the second amplifier which uses VREF to add an

offset voltage to VIN and feedback to add inverting gain. The transfer function for VOUT– is Equation 2.

VOUT+ = VIN

(1)

(2)

The differential output signal, VDIFF, is the difference between the two single-ended output signals, VOUT+ and

VOUT–. Equation 3 shows the transfer function for VDIFF. By applying the conditions that R1 = R2 and R3 = R4, the

transfer function is simplified into Equation 6. Using this configuration, the maximum input signal is equal to the

reference voltage and the maximum output of each amplifier is equal to the VREF. The differential output range is

2×VREF. Furthermore, the common mode voltage will be one half of VREF (see Equation 7).

(3)

VOUT+ = VIN

(4)

VOUT– = VREF – VIN

(5)

VDIFF = 2×VIN – VREF

(6)

(7)

9.1.2.1 Amplifier Selection

Linearity over the input range is key for good dc accuracy. The common mode input range and the output swing

limitations determine the linearity. In general, an amplifier with rail-to-rail input and output swing is required.

Bandwidth is a key concern for this design. Since the NE5532 has a bandwidth of 10 MHz, this circuit will only be

able to process signals with frequencies of less than 10 MHz.

9.1.2.2 Passive Component Selection

Because the transfer function of VOUT– is heavily reliant on resistors (R1, R2, R3, and R4), use resistors with low

tolerances to maximize performance and minimize error. This design used resistors with resistance values of 36

k

Ω with tolerances measured to be within 2%. But, if the noise of the system is a key parameter, the user can

select smaller resistance values (6 k

Ω or lower) to keep the overall system noise low. This ensures that the noise

from the resistors is lower than the amplifier noise.

9.1.3 Application Curves

The measured transfer functions in Figure 5, Figure 6, and Figure 7 were generated by sweeping the input

voltage from 0 V to 12V. However, this design should only be used between 2 V and 10 V for optimum linearity.

Copyright © 1979–2015, Texas Instruments Incorporated

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