OPA314_15 Datasheet, PDF (22/45 Pages) Texas Instruments – OPAx314 3-MHz, Low-Power, Low-Noise, RRIO, 1.8-V CMOS Operational Amplifier

OPA314, OPA2314, OPA4314
SBOS563G – MAY 2011 – REVISED JUNE 2015
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8.2 Typical Application
Some applications require differential signals. Figure 39 shows a simple circuit to convert a single-ended input of
0.1 V to 2.4 V into a differential output of ±2.3 V on a single 2.7-V supply. The output range is intentionally limited
to maximize linearity. The circuit is composed of two amplifiers. One amplifier functions as a buffer and creates a
voltage, V_OUT+. The second amplifier inverts the input and adds a reference voltage to generate V_OUT–. Both
V_OUT+ and V_OUT– range from 0.1 V to 2.4 V. The difference, V_DIFF, is the difference between V_OUT+ and V_OUT–.
This makes the differential output voltage range 2.3 V.
R2
R1
R3
2.7 V
±₊
Device
+
VOUT±
2.7 V
±
+
Device
+
VREF
R4
2.5 V
V V_DIFF
+
VOUT+
VIN
Figure 39. Schematic for a Single-Ended Input to Differential Output Conversion
8.2.1 Design Requirements
The design requirements are as follows:
• Supply voltage: 2.7 V
• Reference voltage: 2.5 V
• Input: 0.1 V to 2.4 V
• Output differential: ±2.3 V
• Output common-mode voltage: 1.25 V
• Small-signal bandwidth: 1 MHz
8.2.2 Detailed Design Procedure
The circuit in Figure 39 takes a single-ended input signal, V_IN, and generates two output signals, V_OUT+ and
V_OUT– using two amplifiers and a reference voltage, V_REF. V_OUT+ is the output of the first amplifier and is a
buffered version of the input signal, V_IN (as shown in Equation 1). V_OUT– is the output of the second amplifier
which uses V_REF to add an offset voltage to V_IN and feedback to add inverting gain. The transfer function for
V_OUT– is given in Equation 2.
V_OUT V_IN
(1)
V_287±
V₅₍₎
u
§
¨
©
R₄
R₃  R₄
·
¸
¹
u
§
¨^1
©
R₂
R₁
·
¸
¹
V_,1
u ^R2
R₁
(2)
22
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