OPA2836-Q1 Datasheet, PDF (31/44 Pages) Texas Instruments – Very-Low Power, Rail-to-Rail Out, Negative-Rail In, Voltage-Feedback Operational Amplifier

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Application Information (continued)
OPA2836-Q1
SBOS794 – DECEMBER 2016
V_SIG-
V_CM
R_G
V_IN-
V_IN+
R_G
V_CM
V_SIG+
R_F
R_F
OPA2836-Q1
V_OUT
G[(V_SIG+)-(V_SIG-)]
V_REF
V_REF
Copyright © 2016, Texas Instruments Incorporated
Figure 65. Differential to Single Ended Amplifier
Line termination can be accomplished with a resistor shunt across the input. The differential input impedance of
the circuit is the resistor value in parallel with the amplifier circuit. For low-gain and low-line impedance, the
resistor value to add is approximately the impedance of the line. For example, if a 100-Ω Cat5 cable is used with
a gain of 1 amplifier and R_F = R_G = 1 kΩ, adding a 100-Ω shunt across the input gives a differential impedance of
98 Ω that is adequate for most applications.
For best CMRR performance, resistors must be matched. A rule of thumb is CMRR ≈ the resistor tolerance; so a
0.1% tolerance provides approximately 60-dB CMRR.
9.1.7 Differential-to-Differential Amplifier
Figure 66 shows a differential amplifier that is used to amplify differential signals. This circuit has high input
impedance and is often used in differential line driver applications where the signal source is a high-impedance
driver (for example, a differential DAC) that must drive a line.
If V_IN± = V_CM + V_SIG± , then the output of the amplifier can be calculated according to Equation 6.
æ
VOUT _±
=
V_IN±
´ç1
è
+
2R_F
R_G
ö
÷
ø
+
V_CM
(6)
G = 1 + ^2RF
The signal gain of the circuit is set by
R_{G , and VCM passes with unity gain. The amplifier in essence}
combines two noninverting amplifiers into one differential amplifier with the R_G resistor shared, which makes R_G
effectively half the value when calculating the gain. The output signals are in-phase with the input signals.
V_IN-
V_SIG-
V_CM
R_G
V_CM
V_SIG+
V_IN+
½ OPA2836-Q1
R_F
R_F
½ OPA2836-Q1
V_OUT-
GV_SIG-
V_CM
V_CM
GV_SIG+
V_OUT+
Copyright © 2016, Texas Instruments Incorporated
Figure 66. Differential to Differential Amplifier
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: OPA2836-Q1
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