LT1223 Linear Technology, LT1223 Datasheet - Page 9

• Manufacturer Part Number: LT1223
• Description: 100MHz Current Feedback Amplifier
• Manufacturer: Linear Technology

A
have about 2.5mV thermal tail on a 10V step. Unfortu-
nately, reducing the input signal and increasing the gain
always results in a thermal tail of about the same amount
for a given output step. For this reason we show separate
graphs of 10mV and 1mV non-inverting amplifier settling
times. Just as the bandwidth of the LT1223 is fairly
constant for various closed-loop gains, the settling time
remains constant as well.
Adjustable Gain Amplifier
To make a variable gain amplifier with the LT1223, vary the
value of R
controlled resistor, a FET, or any other low capacitance
variable resistor. The value of R
change the gain. If R
be reduced at maximum gain and the circuit will oscillate
when R
Adjustable Bandwidth Amplifier
Because the resistance at the inverting input determines
the bandwidth of the LT1223, an adjustable bandwidth
circuit can be made easily. The gain is set as before with
R
resistor is at a minimum.
F
PPLICATI
and R
F
G
is very small.
G
; the bandwidth is maximum when the variable
. The implementation of R
V
R
G
IN
O
V
IN
R
U
G
F
5k
is changed, then the bandwidth will
S
+
–
LT1223
+
–
I FOR ATIO
R
LT1223
U
F
R
F
F
should not be varied to
LT1223 • TA03
W
G
can be a pot, a light
V
LT1223 • TA04
OUT
V
OUT
U
Accurate Bandwidth Limiting The LT1223
It is very common to limit the bandwidth of an op amp by
putting a small capacitor in parallel with R
A SMALL CAPACITOR FROM THE INVERTING INPUT OF
A CURRENT FEEDBACK AMPLIFIER TO ANYWHERE ELSE,
ESPECIALLY NOT TO THE OUTPUT. The capacitor on the
inverting input will cause peaking or oscillations. If you
need to limit the bandwidth of a current feedback amplifier,
use a resistor and capacitor at the noninverting input (R1
& C1). This technique will also cancel (to a degree) the
peaking caused by stray capacitance at the inverting input.
Unfortunately, this will not limit the output noise the way
it does for the op amp.
Current Feedback Amplifier Integrator
Since we remember that the inverting input wants to see
a resistor, we can add one to the standard integrator
circuit. This generates a new summing node where we can
apply capacitive feedback. The LT1223 integrator has
excellent large signal capability and accurate phase shift at
high frequencies.
BW = 5MHz
R1 = 300
C1 = 100pF
V
IN
V
V
V
OUT
IN
IN
=
sC R
R1
1
R
I
I
I
C1
R
1k
F
R
G
+
–
LT1223
+
–
LT1223
C
I
R
F
LT1223 • TA06
F
LT1223 • TA05
. DO NOT PUT
V
OUT
V
LT1223
OUT
9