THS4130, THS4131

HIGHSPEED, LOW NOISE, FULLY DIFFERENTIAL I/O AMPLIFIERS

SLOS318E − MAY 2000 − REVISED JANUARY 2004

19

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

theory of operation (continued)

The following schematics depict the differences between the operation of the THS413x, fully differential

amplifier, in two different modes. Fully differential amplifiers can work with differential input or can be

implemented as single in/differential out.

−

Rf

R(g)

+

+

−

VCC−

VCC+

R(g)

Rf

Vs

VIN−

VIN+

VO+

VO−

VOCM

Note: For proper operation, maintain symmetry by setting

Rf1 = Rf2 = Rf and R(g)1 = R(g)2 = R(g) ⇒ A = Rf/R(g)

Figure 37. Amplifying Differential Signals

−

Rf

R(g)

+

+

−

VCC−

VCC+

R(g)

Rf

Vs

VIN−

VIN+

VO+

VO−

VOCM

GAIN

R(g) Ω

Rf Ω

1

2

5

10

390

374

402

402

390

750

2010

4020

RECOMMENDED RESISTOR VALUES

Figure 38. Single In With Differential Out

If each output is measured independently, each output is one-half of the input signal when gain is 1. The

following equations express the transfer function for each output:

V

O +

1

2

V

I

The second output is equal and opposite in sign:

V

O +

– 1

2

V

I