OPA835IDBVT datasheet(31/63 Pages) TI2

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VOUT+

VOUT-

VREF

VIN

VSIG

VREF

-G x V SIG

VREF

G x VSIG

½OPA2835

Figure 9-2. Single-Ended to Differential Amplifier

Line termination on the output can be accomplished with resistors RO. The differential impedance seen from the

line will be 2 × RO. For example, if 100-Ω Cat5 cable is used with double termination, the amplifier is typically

set for a differential gain of 2 V/V (6 dB) with RF = 0 Ω (short) RG = ∞Ω (open), 2R = 2 kΩ, R1 = 0 Ω, R = 1

kΩ to balance the input bias currents, and RO = 49.9 Ω for output line termination. This configuration is shown in

Figure 9-3.

For driving a differential-input ADC the situation is similar, but the output resistors, RO, are selected with a

capacitor across the ADC input for optimum filtering and settling-time performance.

OUT

49.9 Ω

OUT

2 kΩ

REF

SIG

REF

-G x V

SIG

REF

G x VSIG

½OPA2835

2 kΩ

49.9 Ω

Figure 9-3. Cat5 Line Driver With Gain = 2 V/V (6 dB)

9.1.6 Differential to Single-Ended Amplifier

Figure 9-4 shows a differential amplifier that converts differential signals to single-ended and provides gain

(or attenuation) and level shifting. This circuit can be used in applications like a line receiver for converting a

differential signal from a Cat5 cable to a single-ended signal.

If VIN+ = VCM + VSIG+ and VIN– = VCM + VSIG–, then the output of the amplifier may be calculated according to

Equation 5.

(

)

´ ç

OUT

IN+

REF

+ V

(5)

The signal gain of the circuit is

G =

, VCM is rejected, and VREF provides a level shift around which the

output signal swings. The single-ended output signal is in-phase with the differential input signal.

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OPA835, OPA2835

SLOS713J – JANUARY 2011 – REVISED MARCH 2021

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