Table 8-1 provides the following benefits of using OPAx863A in an MFB low-pass filter circuit:

• High-precision measurements with low offset voltage across the operating temperature range for low-

frequency signals in pass band

• High linearity due to the larger GBW and loop gain for low-frequency signals in pass band

• Higher accuracy of cutoff frequency and smaller variations over process and temperature

• Small integrated output noise due to low-pass filtering

Based on Figure 8-2, and as with the OPAx863A, use an amplifier with a gain bandwidth product at least

20 × greater than the filter cutoff frequency. This configuration results in a high-precision and high-linearity,

low-pass-filter design.

8.2.1.3 Application Curves

Frequency (Hz)

-12

-9

-6

-3

0

3

6

1M

TLV9051

LMV641

OPA2834

OPAx863A

OPA836

Figure 8-2. MFB Low-Pass Filter Frequency Response vs GBW

8.2.2 Low-Power SAR ADC Driver and Reference Buffer

Figure 8-3 shows the use of the OPAx863A as a SAR ADC input driver driving the .ADS7057 sensors, which

are used for interface with the physical environment, exhibit high output impedance, and cannot drive SAR ADC

inputs directly. A wide-GBW amplifier, such as the OPAx863A, is needed to charge the switching capacitors

at the SAR ADC input, and quickly settle to the required accuracy within the given acquisition time. The

OPAx863A wide-GBW, high precision performance enables fast settling, high accuracy sensor measurements,

and reference buffering for precision ADCs.

ADS7057

14-bit

2.5 MSPS

R

S

+

–

3.3 V

AVDD

OPAx863A

C

CB

C

FILT

REF1933

3.3-V

Reference

5V

R

F

R

G

Z

OUT

Sensor

3.3 V

R

S

Figure 8-3. OPAx863A as a Precision SAR ADC Driver

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OPA863A, OPA2863A

SBOSA95D – MAY 2022 – REVISED DECEMBER 2023

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