OPA2316 Datasheet, PDF (22/46 Pages) Texas Instruments – OPAx316 10-MHz, Low-Power, Low-Noise, RRIO, 1.8-V CMOS Operational Amplifier

OPA316, OPA2316, OPA2316S, OPA4316
SBOS703D – APRIL 2014 – REVISED DECEMBER 2014
www.ti.com
Typical Application (continued)
The differential output signal, Vdiff, is the difference between the two single-ended output signals, Vout+ and
Vout–. Equation 3 shows the transfer function for Vdiff. By 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 Vref. The differential output range is 2 ×
Vref. Furthermore, the common-mode voltage is one half of Vref (see Equation 7). TBD Equation 4 and
Equation 5 need text references
Vdiff
Vout   Vout
Vin
u
§
¨©¹

R2
R1
·
¸¹

Vref
u
§
¨
©
R4
R3  R4
·
¸
¹
u
§
¨©¹

R2
R1
·
¸¹
(3)
Vout Vin
(4)
Vout  Vref Vin
(5)
Vdiff  2 K Vin Vref
(6)
Vcm
§ Vout   Vout  ·
¨©
2
¸¹
1 _Vref
2
(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 OPA316 is selected because its 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 Vout– 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 (TBD this what?) ensures that
the noise from the resistors is lower than the amplifier noise.
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