2.7 V

2.7 V

R3

R4

R1

R2

VOUT+

VOUT±

V

+

VDIFF

VREF

2.5 V

VIN

+

±

+

Device

+

±

+

Device

C3

33 pF

V+

GND

3

1

8

4

5

6

7

–IN

+IN

2

C2

DCLOCK

Serial

Interface

1000 pF

R1

1.5 k

R4

20 k

R5

20 k

R6

100 kΩ

R8

150 k

R9

510 k

R7

51 k

DOUT

VREF

V+ = 2.7 V to 5 V

CS/SHDN

C1

1000 pF

Electret

Microphone(1)

G = 100

Passband 300 Hz to 3 kHz

R3

1 M

R2

1 M

ADS7822

12-Bit A/D

1/2

OPA2348-Q1

1/2

OPA2348-Q1

OPA348-Q1, OPA2348-Q1, OPA4348-Q1

www.ti.com

SBOS465C – JANUARY 2009 – REVISED JANUARY 2016

Application Information (continued)

(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, VOUT+. The second amplifier inverts the input and adds a reference voltage to generate VOUT–. Both

VOUT+ and VOUT– range from 0.1 V to 2.4 V. The difference, VDIFF, is the difference between VOUT+ and VOUT–.

This configuration makes the differential output voltage range to be 2.3 V.

Figure 28. Schematic for a Single-Ended Input to Differential Output Conversion

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