AD8021 datasheet(20/28 Pages) AD

20 / 28 page

ADA4896-2/ADA4897-1

Rev. 0 | Page 20 of 28

CAPACITANCE DRIVE

Putting a small snub resistor (RSNUB) in series with the amplifier

output and the capacitive load mitigates the problem. Figure 48

shows the effect of using a snub resistor (RSNUB) on reducing the

peaking for the worst-case frequency response (gain of +2).

Using RSNUB = 100 Ω eliminates the peaking entirely, with the

trade-off that the closed-loop gain is reduced by 0.8 dB due to

attenuation at the output. RSNUB can be adjusted from 0 Ω to

100 Ω to maintain an acceptable level of peaking and closed-

loop gain, as shown in Figure 48.

Capacitance at the output of an amplifier creates a delay

within the feedback path that, if within the bandwidth of

the loop, can create excessive ringing and oscillation. The

ADA4897-1/ADA4896-2 show the most peaking at a gain

of +2, as demonstrated in Figure 8.

–5

–4

–3

–2

–1

FREQUENCY (Hz)

100k

10M

100M

RSNUB = 50Ω

RSNUB = 0Ω

RSNUB = 100Ω

ADA4896-2

1kΩ

249Ω

39pF

RSNUB

VIN

VOUT

VS = 5V

VOUT = 200mV p-p

G = +2

Figure 48. Using a Snub Resistor to Reduce Peaking Due to Output Capacitive Load

AD8021 Datasheet(PDF) 20 Page - Analog Devices