LT1251 Datasheet, PDF (1/24 Pages) Linear Technology – 40MHz Video Fader and DC Gain Controlled Amplifier

LT1251/LT1256
40MHz Video Fader and
DC Gain Controlled Amplifier
FEATURES
s _{Accurate Linear Gain Control: ±1% Typ, ±3% Max}
s _{Constant Gain with Temperature}
s _{Wide Bandwidth: 40MHz}
s _{High Slew Rate: 300V/µs}
s _{Fast Control Path: 10MHz}
s _{Low Control Feedthrough: 2.5mV}
s _{High Output Current: 40mA}
s _{Low Output Noise}
45nV/√Hz at A_V = 1
270nV/√Hz at A_V = 100
s _{Low Distortion: 0.01%}
s _{Wide Supply Range: ±2.5V to ±15V}
s _{Low Supply Current: 13mA}
s _{Low Differential Gain and Phase: 0.02%, 0.02°}
U
APPLICATIONS
s _{Composite Video Gain Control}
s _{RGB, YUV Video Gain Control}
s _{Video Faders, Keyers}
s _{Gamma Correction Amplifiers}
s _{Audio Gain Control, Faders}
s _{Multipliers, Modulators}
s _{Electronically Tunable Filters}
, LTC and LT are registered trademarks of Linear Technology Corporation.
DESCRIPTION
The LT^®1251/LT1256 are 2-input, 1-output, 40MHz cur-
rent feedback amplifiers with a linear control circuit that
sets the amount each input contributes to the output.
These parts make excellent electronically controlled vari-
able gain amplifiers, filters, mixers and faders. The only
external components required are the power supply by-
pass capacitors and the feedback resistors. Both parts
operate on supplies from ±2.5V (or single 5V) to ±15V
(or single 30V).
Absolute gain accuracy is trimmed at wafer sort to mini-
mize part-to-part variations. The circuit is completely
temperature compensated.
The LT1251 includes circuitry that eliminates the need for
accurate control signals around zero and full scale. For
control signals of less than 2% or greater than 98%, the
LT1251 sets one input completely off and the other
completely on. This is ideal for fader applications because
it eliminates off-channel feedthrough due to offset or gain
errors in the control signals.
The LT1256 does not have this on/off feature and operates
linearly over the complete control range. The LT1256 is
recommended for applications requiring more than 20dB
of linear control range.
TYPICAL APPLICATION
Two-Input Video Fader
1
IN1
2
0V TO 2.5V ³
CONTROL
4
I_C
5
6
NULL
V^{– 7}
LT1251/LT1256
+
1
2
–
CONTROL
+
C
I_C IFS
FS
–
5k
5k
14
IN2
13
12 2.5VDC
INPUT
11 _IFS
10
9 _V+
8
R_F2 R_F1
1.5k 1.5k
V_OUT
1251/56 TA01
LT1256
Gain Accuracy vs Control Voltage
5
4
V_S = ±5V
V_FS = 2.5V
3
2
1
0
–1
–2
–3
( )^{( ) –4}
GAIN ACCURACY (%) =
A_VMEAS
–
V_C
2.5
100
–5
0
0.5 1.0 1.5 2.0 2.5
CONTROL VOLTAGE (V)
1251/56 TA02
1