lt6203is8-trpbf Linear Technology Corporation, lt6203is8-trpbf Datasheet - Page 15

• Manufacturer Part Number: lt6203is8-trpbf
• Description: Single/dual/quad 100mhz, Rail-to-rail Input And Output, Ultralow 1.9nvrthz Noise, Low Power Op Amps
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
Amplifier Characteristics
Figure 1 shows a simplified schematic of the LT6202/
LT6203/LT6204, which has two input differential amplifi-
ers 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 V
source I
is maintained through the Q2/Q3 differential amplifier, but
with an input g
with I
1.5V of the negative rail. The effect of the g
a shift in the V
2
when the common mode voltage swings within
1
saturates and current in Q1/Q4 is zero. Feedback
OS
m
DESD1
DESD3
reduction of 1/2. A similar effect occurs
+
–
as I
U
–V
–V
1
or I
+V
+V
U
D1
2
DESD2
DESD4
saturate.
D2
W
CC
Q1
R3
R1
– 1.5V, current
m
Q2
reduction is
I
Figure 1. Simplified Schematic
1
U
I
Q3
2
R2
Q4
R4
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 mirror
that converts the input stage differential signals to a single
ended output. Capacitor C1 reduces the unity cross
frequency and improves the frequency stability without
degrading the gain bandwidth of the amplifier. The
differential drive generator supplies current to the output
transistors that swing from rail-to-rail.
Q8
Q5
C1
R5
D3
+V
Q9
LT6202/LT6203/LT6204
Q7
Q6
+
C
DIFFERENTIAL
–
GENERATOR
M
V
DRIVE
BIAS
Q11
Q10
V –
V
–V
+
+V
DESD6
6203/04 F01
DESD5
15
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