Datasheet

ADA4862-3
Rev. A | Page 12 of 16
Option 2
Another option exists for running the ADA4862-3 as a unity-
gain amplifier. In this configuration, the noise gain is 2, see
Figure 34. The frequency response and transient response for
this configuration closely match the gain of +2 plots because the
noise gains are equal. This method does have twice the noise
gain of Option 1; however, in applications that do not require
low noise, Option 2 offers less peaking and ringing. By tying the
inputs together, the net gain of the amplifier becomes 1.
Equation 1 shows the transfer characteristic for the schematic
shown in
Figure 34. Frequency and transient response are
shown in
Figure 35 and Figure 36.
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+
+
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
=
G
G
F
i
G
F
i
O
R
RR
V
R
R
VV
(1)
which simplifies to V
O
= V
i
.
0.01μF
0.01μF
V
IN
R
T
V
OUT
+V
S
–V
S
GAIN OF +1
05600-030
10μF
10μF
R
F
R
G
Figure 34. Unity Gain of Option 2
1
–7
0.1
1000
FREQUENCY (MHz)
GAIN (dB)
1 10 100
0
–1
–2
–3
–4
–5
–6
G = +1
R
L
= 150Ω
05600-027
Figure 35. Frequency Response of Option 2
05600-039
G = +1
V
S
= ±5V
R
L
= 150Ω
TIME = 2ns/DIV
200
OUTPUT VOLTAGE (mV)
150
100
50
0
–50
–100
–150
–200
Figure 36. Small Signals Transient Response of Option 2
0.01μF
0.01μF
V
IN
R
T
V
OUT
+V
S
–V
S
GAIN OF –1
05600-031
10μF
10μF
Figure 37. Inverting Configuration (G = −1)
2.0
–2.0
OUTPUT VOLTAGE (V)
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
C
L
= 9pF
C
L
= 6pF
C
L
= 4pF
G = –1
R
L
= 150Ω
V
OUT
= 2V p-p
V
S
= ±5V
TIME = 5ns/DIV
05600-017
Figure 38. Large Signal Transient Response for Various Capacitor Loads