LT1228 Ver la hoja de datos (PDF) - Linear Technology

Número de pieza

componentes Descripción

Lista de partido

LT1228

100MHz Current Feedback Amplifier with DC Gain Control

Linear Technology 

LT1228

APPLICATIONS INFORMATION

show the effect of loading. These graphs also show the

family of curves that result from various values of the

feedback resistor. These curves use a solid line when the

response has less than 0.5dB of peaking and a dashed line

for the response with 0.5dB to 5dB of peaking. The curves

stop where the response has more than 5dB of peaking.

Current Feedback Amp Small-Signal Response

VS = ±15V, RF = RG = 750Ω, RL = 100Ω

Capacitance on the Inverting Input

Current feedback amplifiers want resistive feedback from

the output to the inverting input for stable operation. Take

care to minimize the stray capacitance between the output

and the inverting input. Capacitance on the inverting input

to ground will cause peaking in the frequency response

(and overshoot in the transient response), but it does

not degrade the stability of the amplifier. The amount of

capacitance that is necessary to cause peaking is a func-

tion of the closed-loop gain taken. The higher the gain,

the more capacitance is required to cause peaking. For

example, in a gain of 100 application, the bandwidth can

be increased from 10MHz to 17MHz by adding a 2200pF

capacitor, as shown below. CG must have very low series

resistance, such as silver mica.

At a gain of two, on ±15V supplies with a 750Ω feedback

resistor, the bandwidth into a light load is over 160MHz

without peaking, but into a heavy load the bandwidth re-

duces to 100MHz. The loading has so much effect because

there is a mild resonance in the output stage that enhances

the bandwidth at light loads but has its Q reduced by the

heavy load. This enhancement is only useful at low gain

settings, at a gain of ten it does not boost the bandwidth.

At unity gain, the enhancement is so effective the value of

the feedback resistor has very little effect on the bandwidth.

At very high closed-loop gains, the bandwidth is limited

by the gain-bandwidth product of about 1GHz. The curves

show that the bandwidth at a closed-loop gain of 100 is

10MHz, only one tenth what it is at a gain of two.

VIN

CG

1+

6

CFA

8–

RF

510Ω

RG

5.1Ω

VOUT

LT1228 • TA08

Boosting Bandwidth of High Gain Amplifier

with Capacitance On Inverting Input

49

46

CG = 4700pF

43

40

37

CG = 2200pF

34

31

CG = 0

28

25

22

19

1

10

100

FREQUENCY (MHz)

LT1228 • TA09

1228fd

12

Share Link: