OPA316_16 Datasheet, PDF (22/48 Pages) Texas Instruments – 10-MHz, Low-Power, Low-Noise, RRIO, 1.8-V CMOS Operational Amplifier

OPA316, OPA2316, OPA2316S, OPA4316
SBOS703E – APRIL 2014 – REVISED JUNE 2016
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Vout
Vref
u
§
¨
©
R4
R3 R4
·
¸
¹
u
§
¨©¹
R2 ·
R1 ^¸¹
Vin u ^R2
R1
(2)
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. 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 Vref. The differential output range is 2 × Vref. Furthermore, the common-mode voltage is one
half of Vref (see Equation 7).
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 u 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 ensures that the noise from the
resistors is lower than the amplifier noise.
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