OPA348-Q1 Datasheet, PDF (15/30 Pages) Texas Instruments – OPAx348-Q1 1-MHz 45-μA CMOS Rail-to-Rail Operational Amplifier

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Application Information (continued)
OPA348-Q1, OPA2348-Q1, OPA4348-Q1
SBOS465B – JANUARY 2009 – REVISED DECEMBER 2014
R1
1.5 kΩ
C1
1000 pF
R2
1 MΩ
Electret
Microphone(1)
R3
1 MΩ
V+ = 2.7 V to 5 V
Passband 300 Hz to 3 kHz
R4
20 kΩ
1/2
OPA2348-Q1
R6
100 kΩ
R9
510 kΩ
R7
51 kΩ
R8
150 kΩ
C3
33 pF
1/2
OPA2348-Q1
C2 1000 pF
R5
20 kΩ
G = 100
VREF 1
8 ^V+
7
+IN
2
–IN
ADS7822 ⁶
12-Bit A/D ₅
3
4
DCLOCK
DOUT
CS/SHDN
GND
Serial
Interface
(1) Electret microphone powered by R₁.
Figure 27. Speech Bandpass Filtered Data Acquisition System
8.2 Typical Application
Some applications require differential signals. Figure 28 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 28. Schematic for a Single-Ended Input to Differential Output Conversion
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