OPA314_15 Datasheet, PDF (23/45 Pages) Texas Instruments – OPAx314 3-MHz, Low-Power, Low-Noise, RRIO, 1.8-V CMOS Operational Amplifier

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OPA314, OPA2314, OPA4314
SBOS563G – MAY 2011 – REVISED JUNE 2015
Typical Application (continued)
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. 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 V_REF. The differential output range is 2 ×
V_REF. Furthermore, the common-mode voltage is one half of V_REF (see Equation 7).
V_',))
V_287  V_287±
V_,1
u
§¨_1
©
R₂
R₁
·
¸
¹

V₅₍₎
u
§
¨
©
R₄
R₃  R₄
·
¸
¹
u
¨§^1
R₂
·
¸
© ^R1 ¹
(3)
V_OUT V_IN
(4)
V_287±  V₅₍₎ V_,1
(5)
V_DIFF  2 K V_IN V_REF
(6)
V_CM
§
¨©
V_287

2
V_{287 ±}
·
¸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 OPA2314-Q1 device is selected because its bandwidth is
greater than the target of 1 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.
8.2.3 Application Curves
2.50
2.00
1.50
1.00
0.50
0.00
0.00
0.50
1.00
1.50
Input voltage (V)
2.00
2.50
C027
2.50
2.00
1.50
1.00
0.50
0.00
0.00
0.50
1.00
1.50
Input voltage (V)
2.00
2.50
C027
Figure 40. V_OUT+ vs Input Voltage
Figure 41. V_OUT– vs Input Voltage
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