LT1223CN8 查看數據表（PDF） - Linear Technology

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LT1223CN8

100MHz Current Feedback Amplifier

Linear Technology 

LT1223

APPLICATIO S I FOR ATIO

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 RG. The implementation of RG can be a pot, a light

controlled resistor, a FET, or any other low capacitance

variable resistor. The value of RF should not be varied to

change the gain. If RF is changed, then the bandwidth will

be reduced at maximum gain and the circuit will oscillate

when RF is very small.

V IN

+

LT1223

–

RF

RG

VOUT

LT1223 • TA03

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

RF and RG; the bandwidth is maximum when the variable

resistor is at a minimum.

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 RF. DO NOT PUT

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

and 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.

R1

V IN

+

C1

LT1223

–

R1 = 300Ω

RF

C1 = 100pF

BW = 5MHz

RG

VOUT

LT1223 • TA05

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.

V IN

+

LT1223

–

5k

RG

RF

VOUT

LT1223 • TA04

10

VOUT = 1

VIN sC1R1

R1

VIN

+

LT1223

–

RF

1k

C1

VOUT

LT1223 • TA06

1223fb

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