LT1499CS datasheet(13/20 Pages) LINER

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LT1498/LT1499

14989fe

TYPICAL PERFORMANCE CHARACTERISTICS

±15V Small-Signal Response

±15V Large-Signal Response

5V Small-Signal Response

5V Large-Signal Response

200ns/DIV

14989 G27

VS = 5V

AV = 1

VIN = 20mVP-P AT 50kHz

RL = 1k

2μs/DIV

14989 G28

VS = 5V

AV = 1

VIN = 4VP-P AT 10kHz

RL = 1k

200ns/DIV

14989 G29

VS = 15V

AV = 1

VIN = 20mVP-P AT 50kHz

RL = 1k

2μs/DIV

14989 G30

VS = 15V

AV = 1

VIN = 20VP-P AT 10kHz

RL = 1k

APPLICATIONS INFORMATION

Rail-to-Rail Input and Output

The LT1498/LT1499 are fully functional for an input and

output signal range from the negative supply to the posi-

tive supply. Figure 1 shows a simpliﬁed schematic of the

ampliﬁer. The input stage consists of two differential am-

pliﬁers, a PNP stage (Q1/Q2) and an NPN stage (Q3/Q4)

which are active over different ranges of input common

mode voltage. A complementary common emitter output

stage (Q14/Q15) is employed allowing the output to swing

from rail-to-rail. The devices are fabricated on Linear

Technology’s proprietary complementary bipolar process

to ensure very similar DC and AC characteristics for the

output devices (Q14/Q15).

The PNP differential input pair is active for input common

mode voltages, VCM, between the negative supply to

approximately 1.3V below the positive supply. As VCM

moves further toward the positive supply, the transistor

(Q5) will steer the tail current, I1, to the current mirror

(Q6/Q7) activating the NPN differential pair, and the PNP

differential pair becomes inactive for the rest of the input

common mode range up to the positive supply.

The output is conﬁgured with a pair of complementary

common emitter stages that enables the output to swing

from rail to rail. Capacitors (C1 and C2) form local

feedback loops that lower the output impedance at high

frequencies.

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