LT1256 Linear Technology Corporation, LT1256 Datasheet - Page 13

• Manufacturer Part Number: LT1256
• Description: 40mhz Video Fader And Dc Gain Controlled Amplifier
• Manufacturer: Linear Technology Corporation

APPLICATIONS
In low gain applications, R
the feedback resistors and therefore we can simplify the
equation to:
Note that the denominator causes a gain error due to the
open-loop gain (typically 0.1% for frequencies below
20kHz) and for mismatches in R
match in the feedback resistors results in a 0.25% error at
K = 0.5.
If we set R
at low frequencies) the above equation simplifies to:
This shows that the output fades linearly from input 2,
times its gain, to input 1, times its gain, as K goes from
0 to 1.
If only one input is used (for example, V
grounded, then the gain is proportional to K.
V
where A
V
V
O
O
1
KA
1
R
R
F1
G
V
G
R
V
sR C
1
O
KV
1
= R
OL
V
1
1
OL
1
R
R
F2
KV A
F
F
1
1
1
and assume R
1
U
R
R
R
V
K
1
G
F
F
R
R
1
1
1
INFORMATION
1
G
G
U
1
2
2
1
and
and R
K V
1
R
R
R
K V A
F
F
F
2
2
2
K
2
A
2
OL
F1
2
V
are small compared to
W
2
>> R
and R
V
2
1
F1
1
) and Pin 14 is
F2
R
R
(a 0.1% error
. A 1% mis-
F
G
2
2
U
Note that the denominator is the same as the noninverting
case. In low gain applications, R
compared to the feedback resistors and therefore we can
simplify the equation to:
Again, if we set R
error at low frequencies) the above equation simplifies to:
The 4-resistor difference amplifier yields the same result
as the inverting amplifier case, and the common mode
rejection is independent of K.
Similarly for the inverting case where the noninverting
inputs are grounded and the input voltages V
the normally grounded ends of R
V
O
V
where A
O
General Equation for the Inverting Amplifier Case
1
R
sR C
1
OL
V
O
R
OL
V
R
sR C
G
1
OL
1
KV
R
F1
OL
G
R
R
1
1
R
KV A
R
= R
KV
G
1
F
F
1
1
1
1
R
1
R
F2
1
and
R
G
F
V
1
K
1
R
R
and assume R
F
1
1
1
G
K V
K
2
1
R
R
A
1
F
G
2
V
1
1
LT1251/LT1256
1
R
2
R
F
K V A
G1
2
K
G
1
2
R
R
1
and R
2
G
F
and R
2
1
2
R
R
OL
V
F
2
2
2
K V
>> R
G2
R
R
1
G
F
R
, we get:
2
2
2
and V
2
1
2
F1
are small
K
R
R
1
(a 0.1%
13
G
F
2
2
2
drive
1