APPLICATION INFORMATION

RESISTOR MATCHING

V

CC) )

V

CC–

2

_

+

x1

Output Buffer

Vcm Error

Amplifier

C

R

C

R

x1

Output Buffer

VOUT+

VOUT-

VCC+

VCC-

VIN-

VIN+

30 k

Ω

30 k

Ω

VCC+

VCC-

VOCM

THS4150

THS4151

www.ti.com........................................................................................................................................................... SLOS321G – MAY 2000 – REVISED MARCH 2009

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

depends on matched ratios of the resistors. 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:

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 when gain is 1. VOCM has a high bandwidth capability up to the typical operating

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

µF capacitor on the V

OCM

pin as a bypass capacitor. Figure 30 shows the simplified diagram of the THS415x.

Figure 30. THS415x Simplified Diagram

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