ADA4941-1YR-EBZ Ver la hoja de datos (PDF) - Analog Devices

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ADA4941-1YR-EBZ

Single-Supply, Differential 18-Bit ADC Driver

Analog Devices 

ADA4941-1

ADDING A 3-POLE, SALLEN-KEY FILTER

The noninverting amplifier in the ADA4941-1 can be used as

the buffer amplifier of a Sallen-Key filter. A 3-pole, low-pass

filter can be designed to limit the signal bandwidth in front of

an ADC. The input signal first passes through the noninverting

stage where it is filtered. The filtered signal is then passed through

the inverting stage to obtain the complementary output.

Figure 54 illustrates a 3-pole, Sallen-Key, low-pass filter with a

−3 dB cutoff frequency of 100 kHz. The 1.69 kΩ resistor is

included to minimize dc errors due to the input offset current

in A1. The passive RC filters on the outputs are generally

required by the ADC converter that is being driven. The

frequency response of the filter is shown in Figure 55.

OUT+ 4 33Ω

562Ω

VIN

562Ω

3.9nF

3

+5V

10nF 1.69kΩ 1

562Ω

8

FB

VS+

IN A1

VS–

6

2

1kΩ

REF

500Ω

560pF –5V

2.7nF

1kΩ

0.1µF

A2

OUT– 5 33Ω

2.7nF

+

VO, dm

–

0.1µF

Figure 54. Sallen-Key, Low-Pass Filter with 100 kHz Cutoff Frequency

0

VO, dm = 3V p-p

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

10

100

1k

10k 100k

1M

10M 100M

FREQUENCY (Hz)

Figure 55. Frequency Response of the Circuit Shown in Figure 54

Rev. C | Page 21 of 24

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