7
LT1226
U
S
A
O
PP
L
IC
AT
I
WU
U
I FOR ATIO
Compensation for Lower Closed-Loop Gains
frequency domain and in the transient response. The
photo of the small signal response with 1000pF load
shows 55% peaking. The large signal response with a
10,000pF load shows the output slew rate being limited by
the short circuit current.
A
V
= –25, C
L
= 1000pF A
V
= +25, C
L
= 10,000pF
Lag Compensation
V
OS
Null Loop
U
SA
O
PP
L
IC
AT
ITY
P
I
CA
L
The LT1226 can drive coaxial cable directly, but for best
pulse fidelity the cable should be doubly terminated with
a resistor in series with the output.
Compensation
The LT1226 has a typical gain bandwidth product of 1GHz
which allows it to have wide bandwidth in high gain
configurations (i.e., in a gain of 1000 it will have a
bandwidth of about 1MHz). The amplifier is stable in a
noise gain of 25 so the ratio of the output signal to the
inverting input must be 1/25 or less. Straightforward gain
configurations of +25 or –24 are stable, but there are a few
configurations that allow the amplifier to be stable for
lower signal gains (the noise gain, however, remains 25 or
more). One example is the inverting amplifier shown in the
typical applications sections below. The input signal has a
gain of –R
F
/R
IN
to the output, but it is easily seen that this
configuration is equivalent to a gain of –24 as far as the
amplifier is concerned. Lag compensation can also be
used to give a low frequency gain less than 25 with a high
frequency gain of 25 or greater. The example below has a
DC gain of 6, but an AC gain of +31. The break frequency
of the RC combination across the amplifier inputs should
be at least a factor of 10 less than the gain bandwidth of the
amplifier divided by the high frequency gain (in this case
1/10 of 1GHz/31 or 3MHz).
Cable Driving
–
+
200Ω
LT1226
330pF
V
IN
V
OUT
5k
LT1226 TA03
A
V
= +6, f < 2MHz
1k
LT1226 TA04
R2
50Ω
IN
V
OUT
V
R1
1.2k
R3
75 Ω
R4
75
Ω
75 CABLE
Ω
LT1226
+
–
–
+
R
C
LT1226
V
IN
V
OUT
LT1226 TA05
R
IN
R
F
R
F
R
IN
A
V
= –
; R
F
≥ 24 × (R
IN
|| R
C
)
V
IN
V
OUT
LT1226 TA06
–
+
LT1226
300k 300k
1
8
10k 10k
25k
25Ω
100pF
100pF
LT1097
–
+
A
V
= 1001
LT1226 AI04
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of circuits as described herein will not infringe on existing patent rights.
