AD8628ART-R2 datasheet(16/24 Pages) AD

16 / 24 page

AD8628/AD8629/AD8630

Rev. E | Page 16 of 24

FREQUENCY (kHz)

100

PEAK-TO-PEAK NOISE

Because of the ping-pong action between auto-zeroing and

chopping, the peak-to-peak noise of the AD8628/AD8629/AD8630

is much lower than the competition. Figure 52 and Figure 53

show this comparison.

en p-p = 0.5μV

BW = 0.1Hz TO 10Hz

TIME (1s/DIV)

Figure 55. Simulation Transfer Function of the Test Circuit

FREQUENCY (kHz)

100

Figure 52. AD8628 Peak-to-Peak Noise

en p-p = 2.3μV

BW = 0.1Hz TO 10Hz

TIME (1s/DIV)

Figure 56. Actual Transfer Function of the Test Circuit

The measured noise spectrum of the test circuit charted in

Figure 56 shows that noise between 5 kHz and 45 kHz is

successfully rolled off by the first-order filter.

TOTAL INTEGRATED INPUT-REFERRED

NOISE FOR FIRST-ORDER FILTER

Figure 53. LTC2050 Peak-to-Peak Noise

NOISE BEHAVIOR WITH FIRST-ORDER

LOW-PASS FILTER

For a first-order filter, the total integrated noise from the

AD8628 is lower than the LTC2050.

The AD8628 was simulated as a low-pass filter (Figure 55) and

then configured as shown in

3dB FILTER BANDWIDTH (Hz)

0.1

100

10k

LTC2050

AD8551

AD8628

Figure 54. The behavior of the

AD8628 matches the simulated data. It was verified that noise is

rolled off by first-order filtering. Figure 55 and Figure 56 show

the difference between the simulated and actual transfer

functions of the circuit shown in Figure 54.

470pF

OUT

100k

Figure 54. Test Circuit: First-Order Low-Pass Filter,

×101 Gain and 3 kHz Corner Frequency

Figure 57. 3 dB Filter Bandwidth in Hz

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