OPA2836-Q1 Datasheet, PDF (29/44 Pages) Texas Instruments – Very-Low Power, Rail-to-Rail Out, Negative-Rail In, Voltage-Feedback Operational Amplifier

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OPA2836-Q1
SBOS794 – DECEMBER 2016
Application Information (continued)
G=
æ
ç^{1 +}
2R_F1
ö
÷
æ
ç
R_F2
ö
÷
The signal gain of the circuit is set by
è
R_{G1 ø è} R_{G2 ø . 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.
V_IN-
V_SIG-
V_CM
R_G1
V_CM
V_SIG+
V_IN+
½ OPA2836-Q1
R_F1
R_F1
½ OPA2836-Q1
R_G2
R_G2
R_F2
R_F2
OPA2836-Q1
V_OUT
G[(V_SIG+)-(V_SIG-)]
V_REF
V_REF
Figure 62. Instrumentation Amplifier
Integrated solutions are available, but the OPA2836-Q1 provides a much lower-power, high-frequency solution.
For best CMRR performance, resistors must be matched. Given that CMRR ≈ the resistor tolerance, a 0.1%
tolerance provides apprximately 60-dB CMRR.
9.1.4 Attenuators
The noninverting circuit of Figure 51 has a minimum gain of 1. To implement attenuation, a resistor divider can
be placed in series with the positive input, and the amplifier can be set for a gain of 1 by shorting V_OUT to V_IN–
and removing R_G. Because the operational amplifier input has high input impedance, the attenuation is set by the
resistor divider.
The inverting circuit of Figure 52 can be used as an attenuator by making R_G larger than R_F. The attenuation is
simply the resistor ratio. For example, a 10:1 attenuator can be implemented with R_F = 1 kΩ and R_G = 10 kΩ.
9.1.5 Single-Ended-to-Differential Amplifier
Figure 63 illustrates an amplifier circuit that is used to convert single-ended signals to differential and that
provides gain and level shifting. This circuit can be used for converting signals to differential in applications (such
as line drivers for Cat5 cabling or for driving differential-input SAR and ΔΣ ADCs).
With V_IN = V_REF + V_SIG , the output of the amplifier can be calculated according to Equation 4.
V_OUT+ = G x V_IN + V_REF
and V_OUT- = -G x V_IN + V_REF
Where: G = 1 + ^RF
R
G
(4)
The differential-signal gain of the circuit is 2 × G, and V_REF provides a reference around which the output signal
swings. The differential output signal is in-phase with the single-ended input signal.
Copyright © 2016, Texas Instruments Incorporated
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