AD8253ARMZ-R7 datasheet(20/24 Pages) AD

20 / 24 page

AD8253

Rev. 0 | Page 20 of 24

AD8253

+15V

+IN

–IN

0.1µF

10µF

0.1µF

REF

VOUT

–15V

In this example, a 1 nF capacitor and a 49.9 Ω resistor create an

antialiasing filter for the AD7612. The 1 nF capacitor also serves

to store and deliver necessary charge to the switched capacitor

input of the ADC. The 49.9 Ω series resistor reduces the burden

of the 1 nF load from the amplifier and isolates it from the kickback

current injected from the switched capacitor input of the AD7612.

Selecting too small a resistor improves the correlation between

the voltage at the output of the AD8253 and the voltage at the

input of the AD7612 but may destabilize the AD8253. A trade-

off must be made between selecting a resistor small enough to

maintain accuracy and large enough to maintain stability.

0.1μF

1nF

49.9Ω

AD7612

ADR435

+12V

–12V

+5V

+15V

–15V

+IN

–IN

10μF0.1µF

REF

AD8253

DGND

Figure 58. RFI Suppression

Values of R and CC should be chosen to minimize RFI.

Mismatch between the R × CC at the positive input and the

R × CC at negative input degrades the CMRR of the AD8253.

By using a value of CD that is 10 times larger than the value of

CC, the effect of the mismatch is reduced and performance is

improved.

DRIVING AN ANALOG-TO-DIGITAL CONVERTER

An instrumentation amplifier is often used in front of an analog-

to-digital converter to provide CMRR. Usually, instrumentation

amplifiers require a buffer to drive an ADC. However, the low

output noise, low distortion, and low settle time of the AD8253

make it an excellent ADC driver.

Figure 59. Driving an ADC

AD8253ARMZ-R7 Datasheet(PDF) 20 Page - Analog Devices

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