Data Sheet

ADAF1080

APPLICATIONS INFORMATION

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Rev. 0 | 29 of 36

OUTPUT ANTI-ALIAS FILTER

The ADAF1080 integrates an output driver to directly drive ADC

inputs without the need for additional active components.

A passive anti-alias low-pass filter is recommended (ROUT and

COUT) to prevent the ADC from aliasing higher frequency noise

and interferers. Choose values for the output resistor (ROUT) and

capacitor (COUT), as shown in Figure 50 and Table 17, according to

the bandwidth and noise requirements in the application. Take ADC

requirements into account for determining these values.

For high bandwidth applications, the ADC sampling event can

be synchronized with the chopping feature of the ADAF1080, as

explained in the Amplifier Synchronization section, to avoid intermo-

dulation distortion, using the SYNC pin set according to Table 15.

Table 17 details typical ROUT and COUT values for different band-

width requirements.

Table 17. Recommended ROUT and COUT Values for Different Filter Bandwidth on the VOUT Pin and Recommended Amplifier Modes

3 dB Bandwidth

ROUT

COUT

Recommended Chopping Mode

1 kHz

16 kΩ

10 nF

SYNC_EN = VDD and SYNC = GND or fSYNC

10 kHz

1.6 kΩ

10 nF

SYNC_EN = VDD and SYNC = or fSYNC

20 kHz

820 Ω

10 nF

SYNC_EN = VDD and SYNC = or fSYNC

25 kHz

620 Ω

10 nF

Chopping disabled: SYNC_EN = GND and SYNC = VDD

External sync: SYNC_EN = VDD and SYNC = fSYNC

100 kHz

200 Ω

8.2 nF

Chopping disabled: SYNC_EN = GND and SYNC = VDD

External sync: SYNC_EN = VDD and SYNC = fSYNC

200 kHz

200 Ω

3.9 nF

Chopping disabled: SYNC_EN = GND and SYNC = VDD

External sync: SYNC_EN = VDD and SYNC = fSYNC

1 MHz

200 Ω

750 pF

Chopping disabled: SYNC_EN = GND and SYNC = VDD

External sync: SYNC_EN = VDD, SYNC = fSYNC

2 MHz

200 Ω

330 pF

Chopping disabled: SYNC_EN = GND and SYNC = VDD

External sync: SYNC_EN = VDD and SYNC = fSYNC