OPA316-Q1 Datasheet, PDF (23/39 Pages) Texas Instruments – 10-MHz, Rail-to-Rail Input/Output, Low-Voltage, 1.8-V CMOS Operational Amplifier

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OPA316-Q1, OPA2316-Q1, OPA4316-Q1
SBOS841A – NOVEMBER 2016 – REVISED JANUARY 2017
The differential output signal (V_DIFF) is the difference between the two single-ended output signals (V_OUT+ and
V_OUT–). Equation 3 shows the transfer function for V_DIFF. Using conditions in Equation 4 and Equation 5 and
applying the conditions that R₁ = R₂ and R₃ = R₄, the transfer function is simplified into Equation 6. Using this
configuration, the maximum input signal is equal to the reference voltage, and the maximum output of each
amplifier is equal to V_REF. The differential output range is 2 × V_REF. Furthermore, the common-mode voltage is
one half of V_REF, as shown in Equation 7.
V_DIFF V_OUT
V_OUT
VIN
u
§
¨¹
©
R₂
·
¸
R_{1 ¹}
V_REF
u
§
¨
©
R₄
R₃ R₄
·
¸
¹
u
§
¨¹
©
R₂
·
¸
R_{1 ¹}
(3)
V_OUT V_IN
(4)
V_OUT V_REF V_IN
(5)
V_DIFF 2 u V_IN V_REF
(6)
V_CM
§
¨©
V_OUT
V_OUT
2
·
¸¹
1
2
V_REF
(7)
8.2.2.1 Amplifier Selection
Linearity over the input range is key for good dc accuracy. The common-mode input range and output swing
limitations determine the linearity. In general, an amplifier with rail-to-rail input and output swing is required.
Bandwidth is a key concern for this design, so the OPAx316-Q1 is selected because the bandwidth is greater
than the target of 5 MHz. The bandwidth and power ratio makes this device power efficient and the low offset
and drift ensure good accuracy for moderate precision applications.
8.2.2.2 Passive Component Selection
Because the transfer function of V_OUT– is heavily reliant on resistors (R₁, R₂, R₃, and R₄), use resistors with low
tolerances to maximize performance and minimize error. This design uses resistors with resistance values of
49.9-kΩ and tolerances of 0.1%. However, if the noise of the system is a key parameter, smaller resistance
values (6-kΩ or lower) can be selected to keep the overall system noise low. This ensures that the noise from the
resistors is lower than the amplifier noise.
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