OPA690 datasheet(17/35 Pages) TI2

17 / 35 page

OPA2613

SBOS249H − JUNE 2003 − REVISED AUGUST 2008

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1/2

OPA2613

+5V

VS /2

806

Ω

100

Ω

57.6

Ω

806

Ω

402

Ω

402

Ω

0.1

µF

0.1

µF

6.8

µF

0.1

µF

Figure 3. AC-Coupled, G = +2, Single-Supply,

Specification and Test Circuit

The last configuration used as the basis of the +5V

Electrical and Typical Characteristics is shown in Figure 4.

Design considerations for this inverting, bipolar supply

configuration

are

covered

either

single-supply

configuration (as shown in Figure 3) or in the Inverting

Amplifier Operation section.

1/2

OPA2613

+5V

S /2

806

Ω

100

Ω

806

Ω

402

Ω

57.6

Ω

6.8

µF

0.1

µF

0.1

µF

0.1

µF

402

Ω

Figure 4. AC-Coupled, G = −1, Single-Supply,

Specification and Test Circuit

DIFFERENTIAL INTERFACE APPLICATIONS

Dual op amps are particularly suitable to differential input

to differential output applications. Typically, these fall into

either Analog-to-Digital Converter (ADC) input interface or

line driver applications. Two basic approaches to

differential I/O are noninverting or inverting configurations.

Since the output is differential, the signal polarity is

somewhat meaningless—the noninverting and inverting

terminology applies here to where the input is brought into

the OPA2613. Each has its advantages and disadvan-

tages. Figure 5 shows a basic starting point for

noninverting input differential I/O applications.

402

Ω

402

Ω

1/2

OP A2613

Power−Supply

decoupling not

shown.

−V

268

Ω

1/2

OP A2613

Figure 5. Noninverting Differential I/O Amplifier

This

approach

provides

for

source termination

impedance that is independent of the signal gain. For

instance, simple differential filters may be included in the

signal path right up to the noninverting inputs without

interacting with the gain setting. The differential signal gain

for the circuit of Figure 5 is:

+ 1 ) 2

Since the OPA2613 is a voltage-feedback (VFB) amplifier,

its bandwidth is principally controlled by the noise gain.

The equivalent noise gain for Figure 5 is:

) 2

402

268

W +

4V V

Various combinations of single-supply or AC-coupled gain

can also be delivered using the basic circuit of Figure 5.

Common-mode bias voltages on the two noninverting

inputs pass on to the output with a gain of 1 since an equal

DC voltage at each inverting node creates no current

through RG. This circuit does show a common-mode gain

of 1 from input to output. The source connection should

either remove this common-mode signal if undesired

(using an input transformer can provide this function), or

the common-mode voltage at the inputs can be used to set

the output common-mode bias. If the low common-mode

rejection of this circuit is a problem, the output interface

may also be used to reject that common-mode. For

instance, most modern differential input ADCs reject

common-mode signals very well, while a line driver

application through a transformer will also remove the

common-mode signal through to the line.

(1)

(2)

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