LT1251 데이터 시트보기 (PDF) - Linear Technology
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LT1251 Datasheet PDF : 24 Pages
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LT1251/LT1256
APPLICATIONS INFORMATION
Signal Path Description
RG1
RF1
I1
R1
2–
1
V1 1 +
V2 14 +
2
13 –
I2 R2
RG2
RF2
I1
K
Σ IO
8
+1
VO
I2 1 – K
ROL
C
1251/56 BD
Figure 2. Signal Path Block Diagram
Figure 2 is the basic block diagram of the LT1251/LT1256
signal path with external resistors RG1, RF1, RG2 and RF2.
Both input stages are operating as noninverting amplifiers
with two input signals V1 and V2.
Each input stage has a unity-gain buffer from the nonin-
verting input to the inverting input. Therefore, the inverting
input is at the same voltage as the noninverting input. R1
and R2 represent the internal output resistances of these
buffers, approximately 27Ω.
K is a constant determined by the control circuit and can
be any value between 0 and 1. The control circuit is
described in a later section.
By inspection of the diagram:
( )( ) I1=
R1 +
V1
RG1 RF1
RG1 + RF1
−
RF1
+
VO
R1
RF1
RG1
+ 1
( )( ) I2 =
R2 +
V2
RG2 RF2
RG2 + RF2
−
RF2
+
VO
R2
RF2
RG2
+
1
( ) IO = KI1+ 1− K I2
( )
VO = IO
ROL
1+ sROLC
Substituting and rearranging gives:
( ) KV1
+ 1− K V2
( )( ) ( )( ( ) ) VO
=
R1 +
RG1 RF1
RG1 + RF1
1+ sROLC
ROL
+
RF1
+
K
R1
RF1
RG1
R2
+
RG2 RF2
RG2 + RF2
1− K
+
1
+
RF2
+
R2
RF2
RG2
+ 1
General Equation for the Noninverting Amplifier Case
12
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