THS4131 datasheet(14/27 Pages) TI

14 / 27 page

THS4130, THS4131

HIGHSPEED, LOW NOISE, FULLY DIFFERENTIAL I/O AMPLIFIERS

SLOS318E − MAY 2000 − REVISED JANUARY 2004

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

resistor matching

Resistor matching is important in fully differential amplifiers. The balance of the output on the reference voltage

depends on matched ratios of the resistor. CMRR, PSRR, and cancellation of the second harmonic distortion

will diminish if resistor mismatch occurs. Therefore, it is recommended to use 1% tolerance resistors or better

to keep the performance optimized.

VOCM sets the dc level of the output signals. If no voltage is applied to the VOCM pin, it will be set to the midrail

voltage internally defined as:

CC) )

CC–

In the differential mode, the VOCM on the two outputs cancel each other. Therefore, the output in the differential

mode is the same as the input in the gain of 1. VOCM has a high bandwidth capability up to the typical operation

range of the amplifier. For the prevention of noise going through the device, use a 0.1

µF capacitor on the VOCM

pin as a bypass capacitor. The following graph shows the simplified diagram of the THS413x.

Output Buffer

Vcm Error

Amplifier

Output Buffer

VOUT+

VOUT−

VCC+

VCC−

VIN−

VIN+

30 k

Ω

30 k

Ω

VCC+

VCC−

VOCM

Figure 29. THS413x Simplified Diagram

THS4131 Datasheet(PDF) 14 Page - Texas Instruments