7
LT1225
U
S
A
O
PP
L
IC
AT
I
WU
U
I FOR ATIO
domain and in the transient response. The photo of the
small-signal response with 1000pF load shows 50% peak-
ing. The large-signal response with a 10,000pF load shows
the output slew rate being limited by the short-circuit
current.
Lag Compensation
Wein Bridge Oscillator
A
V
= –5, C
L
= 1000pF
A
V
= 5, C
L
= 10,000pF
The LT1225 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 LT1225 has a typical gain-bandwidth product of
150MHz which allows it to have wide bandwidth in high
gain configurations (i.e., in a gain of 10 it will have a
bandwidth of about 15MHz). The amplifier is stable in a
noise gain of 5 so the ratio of the output signal to the
inverting input must be 1/5 or less. Straightforward gain
configurations of 5 or –4 are stable, but there are a few
configurations that allow the amplifier to be stable for
lower signal gains (the noise gain, however, remains 5 or
more). One example is the summing amplifier shown in
the typical applications section below. Each 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 –4 as far as the
amplifier is concerned. Lag compensation can also be
used to give a low frequency gain less than 5 with a high
frequency gain of 5 or greater. The example below has a
DC gain of one, but an AC gain of 5. The break frequency
of the RC combination across the amplifier inputs should
be approximately a factor of 10 less than the gain band-
width of the amplifier divided by the high frequency gain
(in this case 1/10 of 150MHz/5 or 3MHz).
U
SA
O
PP
L
IC
AT
ITY
P
I
CA
L
Cable Driving
Summing Amplifier
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.
LT1225 AI04
LT1225 TA04
R2
250Ω
IN
V
OUT
V
R1
1k
R3
75 Ω
R4
75
Ω
75 CABLE
Ω
LT1225
+
–
–
+
500Ω
LT1225
100pF
V
IN
V
OUT
2k
LT1225 TA03
A
V
= 1, f < 3MHz
–
+
LT1225
100pF
V
OUT
>10V
P-P
1MHz
LT1225 TA05
430Ω
100pF
1.5k
1.5k
#327
LAMP
–
+
LT1225
V
IN1
V
OUT
R
F
LT1225 TA06
R
IN
R
IN
R
IN
V
IN2
V
IN
n
R
IN
=
nR
F
4
