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LOW DISTORTION, LIMITED OUTPUT, ADC INPUT DRIVER

OPA699

V

4

2

3

7

5

8

6

V

+3.5V

+1.5V

REFB

REFT

IN

V

IN

0.1

µF

100pF

V

V

0.1

µF

0.1

µF

18pF

1000pF

4pF

750

Ω

24.9

Ω

374

Ω

562

Ω

102

Ω

1.4k

Ω

1.4k

Ω

102

Ω

562

Ω

ADS822

10-Bit

40MSPS

10-Bit

Data

V

INT/EXT

RSEL

+V

S

GND

S0038-02

LIMITED OUTPUT, DIFFERENTIAL ADC INPUT DRIVER

OPA699M

SGLS289A – MAY 2005 – REVISED MARCH 2006

APPLICATION INFORMATION (continued)

Figure 52 shows a simple ADC driver that operates on a single supply, and gives excellent distortion

performance. The limit voltages track the input range of the converter, completely protecting against input

overdrive. Note that the limiting voltages have been set 100 mV above/below the corresponding reference

voltage from the converter. This circuit also implements an improved distortion for an inverting gain of –2 using

external compensation.

Figure 52. Single Supply, Limiting ADC Input Driver

Figure 53 shows a differential ADC driver that takes advantage of the OPA699 limiters to protect the input of the

ADC. Two OPA699s are used. The first one is an inverting configuration at a gain of –2. The second one is in a

noninverting configuration at a gain of +2. See the Low Gain Compensation for Improved SFDR section for a

magnitude of each amplifier maximum signal to provide input protection for the ADC, while maintaining an

acceptable distortion level.

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