AD8628_05 Datasheet, PDF (16/24 Pages) Analog Devices – Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifier

AD8628/AD8629/AD8630
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.
e_n p-p = 0.5μV
BW = 0.1Hz TO 10Hz
50
45
40
35
30
25
20
15
10
5
0
0 10 20 30 40 50 60 70 80 90 100
FREQUENCY (kHz)
Figure 55. Simulation Transfer Function of the Test Circuit
TIME (1s/DIV)
Figure 52. AD8628 Peak-to-Peak Noise
e_n p-p = 2.3μV
BW = 0.1Hz TO 10Hz
TIME (1s/DIV)
Figure 53. LTC2050 Peak-to-Peak Noise
NOISE BEHAVIOR WITH FIRST-ORDER
LOW-PASS FILTER
The AD8628 was simulated as a low-pass filter (Figure 55) and
then configured as shown in 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.
IN
OUT
100kΩ
470pF
50
45
40
35
30
25
20
15
10
5
0
0 10 20 30 40 50 60 70 80 90 100
FREQUENCY (kHz)
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
For a first-order filter, the total integrated noise from the
AD8628 is lower than the LTC2050.
10
LTC2050
AD8551
AD8628
1
1kΩ
Figure 54. 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 57. 3 dB Filter Bandwidth in Hz
Rev. E | Page 16 of 24