LT1801 datasheet(13/16 Pages) AD

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LT6203X

6203xf

For more information www.linear.com/LT6203X

Amplifier Characteristics

Figure 1 shows a simplified schematic of the LT6203X,

which has two input differential amplifiers in parallel that

are biased on simultaneously when the common mode

voltage is at least 1.5V from either rail. This topology

allows the input stage to swing from the positive supply

voltage to the negative supply voltage. As the common

mode voltage swings beyond VCC – 1.5V, current source

I1 saturates and current in Q1/Q4 is zero. Feedback is

maintained through the Q2/Q3 differential amplifier, but

with an input gm reduction of 1/2. A similar effect occurs

with I2 when the common mode voltage swings within

1.5V of the negative rail. The effect of the gm reduction is

a shift in the VOS as I1 or I2 saturate.

applicaTions inForMaTion

Input bias current normally flows out of the + and – inputs.

The magnitude of this current increases when the input

common mode voltage is within 1.5V of the negative rail,

and only Q1/Q4 are active. The polarity of this current

reverses when the input common mode voltage is within

1.5V of the positive rail and only Q2/Q3 are active.

The second stage is a folded cascode and current mir-

ror that converts the input stage differential signals to a

single ended output. Capacitor C1 reduces the unity cross

frequency and improves the frequency stability with-

out degrading the gain bandwidth of the amplifier. The

differential drive generator supplies current to the output

transistors that swing from rail-to-rail.

DIFFERENTIAL

DRIVE

GENERATOR

–

Q10

Q11

DESD2

DESD4

DESD3

DESD1

DESD5

DESD6

–

VBIAS

–V

V+

V–

6203X F01

Figure 1. Simplified Schematic

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