AD8510/AD8512/AD8513
AD8513 in response to a 400 mV pulse. The circuit is configured in
positive unity gain (worst case) with a load experience of 500 pF.
V
SY
= ±15V
C
L
= 500pF
R
L
=10kΩ
OPEN-LOOP GAIN AND PHASE RESPONSE
In addition to their impressive low noise, low offset voltage, and
offset current, the AD8510/AD8512/AD8513 have excellent
loop gain and phase response even when driving large resistive
and capacitive loads.
Compared with Competitor A (see Figure 49) under the same
conditions, with a 2.5 kΩ load at the output, the AD8510/AD8512/
AD8513 have more than 8 MHz of bandwidth and a phase margin
of more than 52°.
Competitor A, on the other hand, has only 4.5 MHz of band-
width and 28° of phase margin under the same test conditions.
Even with a 1 nF capacitive load in parallel with the 2 kΩ load
at the output, the AD8510/AD8512/AD8513 show much better
response than Competitor A, whose phase margin is degraded
to less than 0, indicating oscillation.
70
60
50
40
V
SY
= ±15V
R
L
= 2.5kΩ
C
L
= 0pF
315
270
225
180
135
90
45
0
VOLTAGE (200mV/DIV)
TIME (1µs/DIV)
Figure 46. Capacitive Load Drive Without Snubber
VOLTAGE (200mV/DIV)
V
SY
= ±15V
R
L
= 10kΩ
C
L
= 500pF
R
S
= 100Ω
C
S
= 1nF
GAIN (dB)
30
20
10
0
–10
–20
–30
10k
100k
1M
FREQUENCY (Hz)
10M
–45
02729-043
02729-044
–90
–135
50M
Figure 48. Frequency Response of the AD8510/AD8512/AD8513
02729-042
70
60
50
40
GAIN (dB)
315
V
SY
= ±15V
R
L
= 2.5kΩ
C
L
= 0pF
270
225
180
135
90
45
0
PHASE (Degrees)
TIME (1µs/DIV)
Figure 47. Capacitive Load with Snubber Network
Optimum values for R
S
and C
S
depend on the load capacitance
and input stray capacitance and are determined empirically.
Table 5. Optimum Values for Capacitive Loads
C
LOAD
500 pF
2 nF
5 nF
R
S
(Ω)
100
70
60
C
S
1 nF
100 pF
300 pF
30
20
10
0
–10
–20
–30
10k
100k
1M
FREQUENCY (Hz)
10M
–45
–90
–135
50M
Figure 49. Frequency Response of Competitor A
Rev. H | Page 15 of 20
PHASE (Degrees)
When the snubber circuit is used, the overshoot is reduced from
55% to less than 3% with the same load capacitance. Ringing is
virtually eliminated, as shown in Figure 47.
02729-041
AD [ ANALOG DEVICES ]
