AD8628/AD8629
50
45
40
35
30
25
20
15
PEAK-TO-PEAK NOISE
Because of the ping-pong action between auto-zeroing and
chopping, the peak-to-peak noise of the AD8628/AD8629 is
much lower than the competition. Figure 50 and Figure 51
show this comparison.
e
p-p = 0.5µV
n
BW = 0.1Hz TO 10Hz
10
5
0
0
10
20
30
40
50
60
70
80
90
100
FREQUENCY (Hz)
Figure 53. Simulation Transfer Function of the Test Circuit
50
45
40
35
30
25
20
15
TIME (1s/DIV)
Figure 50. AD8628 Peak-to-Peak Noise
e
p-p = 2.3µV
n
BW = 0.1Hz TO 10Hz
10
5
0
0
10
20
30
40
50
60
70
80
90
100
FREQUENCY (kHz)
Figure 54. Actual Transfer Function of Test Circuit
The measured noise spectrum of the test circuit 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
TIME (1s/DIV)
Figure 51. LTC2050 Peak-to-Peak Noise
For a first-order filter, the total integrated noise from the
AD8628 is lower than the LTC2050.
NOISE BEHAVIOR WITH FIRST-ORDER LOW-PASS
FILTER
10
The AD8628 was simulated as a low-pass filter and then
configured as shown in Figure 52. The behavior of the AD8628
matches the simulated data. It was verified that noise is rolled
off by first-order filtering.
LTC2050
AD8551
AD8628
IN
1
OUT
100kΩ
1kΩ
470pF
Figure 52. Test Circuit: First-Order Low-Pass Filter—×101 Gain
and 3 kHz Corner Frequency
0.1
10
100
1k
10k
3dB FILTER BANDWIDTH (Hz)
Figure 55. 3 dB Filter Bandwidth in Hz
Rev. C | Page 15 of 20
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