LT1256_15 [Linear]
40MHz Video Fader and DC Gain Controlled Amplifier;
| 型号： | LT1256_15 |
| 厂家： | 
Linear |
| 描述： | 40MHz Video Fader and DC Gain Controlled Amplifier |
| 文件： | 总24页 (文件大小：392K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1251/LT1256
40MHz Video Fader and
DC Gain Controlled Amplifier
U
FEATURES
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).
■
Accurate Linear Gain Control: ±1% Typ, ±3% Max
■
Constant Gain with Temperature
Wide Bandwidth: 40MHz
High Slew Rate: 300V/µs
Fast Control Path: 10MHz
Low Control Feedthrough: 2.5mV
High Output Current: 40mA
Low Output Noise
■
■
■
■
■
■
45nV/√Hz at AV = 1
270nV/√Hz at AV = 100
Low Distortion: 0.01%
Wide Supply Range: ±2.5V to ±15V
Low Supply Current: 13mA
Low Differential Gain and Phase: 0.02%, 0.02°
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.
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APPLICATIONS
■
Composite Video Gain Control
■
RGB, YUV Video Gain Control
■
Video Faders, Keyers
■
Gamma Correction Amplifiers
TheLT1256doesnothavethison/offfeatureandoperates
linearly over the complete control range. The LT1256 is
recommended for applications requiring more than 20dB
of linear control range.
■
Audio Gain Control, Faders
■
■
Multipliers, Modulators
Electronically Tunable Filters
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
LT1256
Two-Input Video Fader
Gain Accuracy vs Control Voltage
5
V
V
= ±5V
FS
S
4
3
= 2.5V
LT1251/LT1256
CONTROL
1
2
3
4
5
6
7
14
13
12
11
10
9
IN1
IN2
+
–
+
–
1
2
2
1
2.5VDC
INPUT
0V TO 2.5V
CONTROL
+
–
+
–
I
FS
I
C
FS
5k
C
0
I
FS
I
R
R
F1
–1
–2
–3
C
F2
1.5k
1.5k
5k
+
V
2.5
NULL
V
C
100
(
–4 GAIN ACCURACY (%) =
A
–
)
VMEAS
(
)
8
–
V
–5
0
0.5
1.0
1.5
2.0
2.5
V
1251/56 TA01
OUT
CONTROL VOLTAGE (V)
1251/56 TA02
1
LT1251/LT1256
W W
U W
U
W U
ABSOLUTE MAXIMUM RATINGS
PACKAGE/ORDER INFORMATION
Total Supply Voltage (V+ to V–) .............................. 36V
Input Current ...................................................... ±15mA
Input Voltage on Pins 3,4,5,10,11,12 ............... V– to V+
Output Short-Circuit Duration (Note 1)........ Continuous
Specified Temperature Range (Note 2)....... 0°C to 70°C
Operating Temperature Range ............... –40°C to 85°C
Storage Temperature Range ................. –65°C to 150°C
Junction Temperature (Note 3)............................ 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
ORDER PART
NUMBER
IN2
FB2
IN1
FB1
1
2
3
4
5
6
7
14
13
12
11
10
9
+
–
+
–
1
2
CONTROL
LT1251CN
LT1251CS
LT1256CN
LT1256CS
+
–
+
–
V
FS
V
C
C
FS
I
FS
I
C
R
R
C
FS
+
V
NULL
(Note 2)
–
V
V
8
OUT
N PACKAGE
14-LEAD PDIP
S PACKAGE
14-LEAD PLASTIC SO
TJMAX = 150°C, θJA = 70°C/ W (N)
JMAX = 150°C, θJA = 100°C/ W (S)
T
Consult factory for Industrial and Military grade parts.
U
W
SIG AL A PLIFIER AC CHARACTERISTICS
0°C ≤ TA ≤ 70°C, VS = ±5V, VIN = 1VRMS, f = 1kHz, AVMAX = 1, RF1 = RF2 = 1.5k, VFS = 2.5V, IC = IFS = NULL = Open, Pins 5,10 = GND,
unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
V (Pin 3) = 0.05V
MIN
TYP
MAX
UNITS
2%IN1
2% Input 1 Gain
LT1251
LT1256
●
●
0
0.1
0.1
5.0
%
%
C
10%IN1
20%IN1
30%IN1
40%IN1
50%IN1
60%IN1
70%IN1
80%IN1
90%IN1
98%IN1
10% Input 1 Gain
20% Input 1 Gain
30% Input 1 Gain
40% Input 1 Gain
50% Input 1 Gain
60% Input 1 Gain
70% Input 1 Gain
80% Input 1 Gain
90% Input 1 Gain
98% Input 1 Gain
V (Pin 3) = 0.25V
●
●
●
●
●
●
●
●
●
7
13
23
33
43
53
63
73
83
93
%
%
%
%
%
%
%
%
%
C
V (Pin 3) = 0.50V
17
27
37
47
57
67
77
87
C
V (Pin 3) = 0.75V
C
V (Pin 3) = 1.00V
C
V (Pin 3) = 1.25V
C
V (Pin 3) = 1.50V
C
V (Pin 3) = 1.75V
C
V (Pin 3) = 2.00V
C
V (Pin 3) = 2.25V
C
V (Pin 3) = 2.45V
C
LT1251
LT1256
●
●
99.9
95.0
100.0
99.9
%
%
2%IN2
2% Input 2 Gain
V (Pin 3) = 2.45V
C
LT1251
LT1256
●
●
0
0.1
0.1
5.0
%
%
10%IN2
20%IN2
30%IN2
40%IN2
50%IN2
60%IN2
70%IN2
80%IN2
90%IN2
98%IN2
10% Input 2 Gain
20% Input 2 Gain
30% Input 2 Gain
40% Input 2 Gain
50% Input 2 Gain
60% Input 2 Gain
70% Input 2 Gain
80% Input 2 Gain
90% Input 2 Gain
98% Input 2 Gain
V (Pin 3) = 2.25V
●
●
●
●
●
●
●
●
●
7
13
23
33
43
53
63
73
83
93
%
%
%
%
%
%
%
%
%
C
V (Pin 3) = 2.00V
17
27
37
47
57
67
77
87
C
V (Pin 3) = 1.75V
C
V (Pin 3) = 1.50V
C
V (Pin 3) = 1.25V
C
V (Pin 3) = 1.00V
C
V (Pin 3) = 0.75V
C
V (Pin 3) = 0.50V
C
V (Pin 3) = 0.25V
C
V (Pin 3) = 0.05V
C
LT1251
LT1256
●
●
99.9
95.0
100.0
99.9
%
%
Gain Drift with Temperature
(Worst Case at 30% Gain)
V (Pin 3) = 0.75V
V (Pin 3) = 0.75V
C
N Package
S Package
50
400
ppm/°C
ppm/°C
C
2
LT1251/LT1256
U
W
SIG AL A PLIFIER AC CHARACTERISTICS
0°C ≤ TA ≤ 70°C, VS = ±5V, VIN = 1VRMS, f = 1kHz, AVMAX = 1, RF1 = RF2 = 1.5k, VFS = 2.5V, IC = IFS = NULL = Open, Pins 5,10 = GND,
unless otherwise noted.
SYMBOL PARAMETER
Gain Supply Rejection
CONDITIONS
V = 1.25V, V = ±5V to ±15V
MIN
TYP
0.03
MAX
0.10
55
UNITS
%/V
%
●
●
C
S
External Resistor Gain
50% Input 1
Pins 5,10 = Open, External 5k Resistors
from Pins 4,11 to Ground, V = 1.25V
45
C
SR
Slew Rate
V
= ±2.5V, V at ±2V, R = 150Ω
●
150
300
2.5
20
30
40
V/µs
mV
P-P
MHz
MHz
MHz
IN
O
L
Control Feedthrough
Full Power Bandwidth
Small-Signal Bandwidth
V = 1.25VDC + 2.5V at 1kHz
V
V = ±5V
V = ±15V
C
O
P-P
= 1V
RMS
BW
S
S
Differential Gain (Notes 4,5)
Differential Phase (Notes 4,5)
Total Harmonic Distortion
Control = 0% or 100%
Control = 25% or 75%
Control = 0% or 100%
Control = 25% or 75%
Gain = 100%
Gain = 50%
Gain = 10%
0.02
0.90
0.02
0.55
0.002
0.015
0.4
%
%
DEG
DEG
%
%
%
THD
t , t
OS
Rise Time, Fall Time
Overshoot
Propagation Delay
Settling Time
10% to 90%, V = 100mV
11
3
10
65
ns
%
ns
ns
r
f
O
V
V
= 100mV
= 100mV
O
t
t
PD
S
O
0.1%, ∆V = 2V
O
U
W
SIG AL A PLIFIER DC CHARACTERISTICS
0°C ≤ TA ≤ 70°C, VS = ±5V, VCM = 0V, VFS = 2.5V, IC = IFS = NULL = Open, Pins 5,10 = GND, unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
OS
Input Offset Voltage
Either Input
Difference Between Inputs
●
●
2
1
5
3
mV
mV
–3
Input Offset Voltage Drift
Noninverting Input Bias Current
Inverting Input Bias Current
10
0.5
10
0.5
–170
2.7
1.5
29
17
1.5
µV/°C
µA
+
I
I
Either Input
Either Input
Difference Between Inputs
Null (Pin 6) Open to V
f = 1kHz
f = 1kHz
f = 1kHz
Either Noninverting Input
Either Noninverting Input
●
–2.5
–30
–1
2.5
30
1
IN
–
●
●
µA
µA
IN
–
Inverting Input Bias Current Null Change
Input Noise Voltage Density
Noninverting Input Noise Current Density
Inverting Input Noise Current Density
Input Resistance
●
–280
–60
µA
nV/√Hz
pA/√Hz
pA/√Hz
MΩ
e
+i
–i
R
C
n
n
n
IN
IN
●
●
5
Input Capacitance
pF
Input Voltage Range
V = ±5V
V = 5V
S
●
●
±3
2
±3.2
V
V
S
3
CMRR
PSRR
Common Mode Rejection Ratio
V
= –3V to 3V
●
●
55
50
61
57
0.07
0.17
76
30
30
dB
dB
µA/V
µA/V
dB
nA/V
nA/V
CM
V = 5V, V = 2V to 3V, V = 2.5V
S
CM
O
Inverting Input Current Common Mode Rejection
V
= –3V to 3V
●
●
0.25
0.70
CM
V = 5V, V = 2V to 3V, V = 2.5V
S
CM
O
Power Supply Rejection Ratio
Noninverting Input Current Power Supply Rejection
Inverting Input Current Power Supply Rejection
V = ±5V to ±15V
●
●
●
70
S
V = ±5V to ±15V
100
200
S
V = ±5V to ±15V
S
3
LT1251/LT1256
U
W
SIG AL A PLIFIER DC CHARACTERISTICS
0°C ≤ TA ≤ 70°C, VS = ±5V, VCM = 0V, VFS = 2.5V, IC = IFS = NULL = Open, Pins 5,10 = GND, unless otherwise noted.
SYMBOL PARAMETER
Large-Signal Voltage Gain
CONDITIONS
V = –3V to 3V, R = 150Ω
MIN
TYP
MAX
UNITS
A
VOL
83
83
0.75
0.75
±4.0
±3.0
±2.75
±14.0
1.2
93
dB
dB
MΩ
MΩ
V
V
V
V
V
O
L
V = –2.75V to 2.75V, R = 150Ω
●
O
L
–
R
OL
Transresistance, ∆V /∆I
V = –3V to 3V, R = 150Ω
1.8
OUT
IN
O
L
V = –2.75V to 2.75V, R = 150Ω
●
●
O
L
V
OUT
Maximum Output Voltage Swing
No Load
R = 150Ω
L
±4.2
±3.5
●
●
●
V = ±15V, No Load
±14.2
S
V = 5V, V = 2.5V, (Note 6)
3.8
S
CM
I
I
Maximum Output Current
Supply Current
V = ±5V
●
●
±30
±20
±40
±30
13.5
7.5
1.3
14.5
1.4
mA
mA
mA
mA
mA
mA
mA
O
S
V = 5V, V = V = 2.5V
S
CM
O
V = V = 2.5V
●
●
●
●
●
17.0
9.5
1.8
18.5
2.0
S
C
FS
V = V = 1.25V
C
FS
V = V = 0V
C
FS
V = V = 2.5V, V = ±15V
C
FS
S
V = V = 0V, V = ±15V
C
FS
S
U
U
W
CO TROL A D FULL SCALE A PLIFIER CHARACTERISTICS
0°C ≤ TA ≤ 70°C, VS = ±5V, VFS = 2.5V, IC = IFS = NULL = Open, Pins 5,10 = GND, unless otherwise noted.
SYMBOL PARAMETER
Control Amplifier Input Offset Voltage
CONDITIONS
Pin 4 to Pin 3
Pin 11 to Pin 12
MIN
TYP
5
5
100
100
–300
–300
5
MAX
15
15
UNITS
mV
mV
MΩ
MΩ
nA
●
●
●
●
●
●
Full-Scale Amplifier Input Offset Voltage
Control Amplifier Input Resistance
Full-Scale Amplifier Input Resistance
Control Amplifier Input Bias Current
Full-Scale Amplifier Input Bias Current
Internal Control Resistor
25
25
–750
–750
3.75
4
nA
kΩ
kΩ
R
R
T = 25°C
6.25
6
C
A
Internal Full-Scale Resistor
T = 25°C
A
5
FS
Resistor Temperature Coefficient
Control Path Bandwidth
Control Path Rise and Fall Time
Control Path Transition Time
0.2
10
35
%/°C
MHz
ns
Small Signal, V = 100mV, (Note 7)
C
Small Signal, V = 100mV, (Note 7)
C
0% to 100%
150
ns
Control Path Propagation Delay
Small Signal, ∆V = 100mV
V from 0% or 100%
C
50
90
ns
ns
C
The
● denotes specifications which apply over the specified operating
Note 4: Differential gain and phase are measured using a Tektronix
TSG120YC/NTSC signal generator and a Tektronix 1780R Video
temperature range.
Measurement Set. The resolution of this equipment is 0.1% and 0.1°. Five
identical amplifier stages were cascaded giving an effective resolution of
0.02% and 0.02°.
Note 5: Differential gain and phase are best when the control is set at 0%
or 100%. See the Typical Performance Characteristics curves.
Note 1: A heat sink may be required depending on the power supply
voltage.
Note 2: Commercial grade parts are designed to operate over the
temperature range of –40°C to 85°C but are neither tested nor guaranteed
beyond 0°C to 70°C. Industrial grade parts specified and tested over
–40°C to 85°C are available on special request. Consult factory.
Note 6: Tested with R = 150Ω to 2.5V to simulate an AC coupled load.
L
Note 3: T is calculated from the ambient temperature T and the power
Note 7: Small-signal control path response is measured driving R (Pin 5)
to eliminate peaking caused by stray capacitance on Pin 4.
J
A
C
dissipation P according to the following formulas:
D
LT1251CN/LT1256CN:
LT1251CS/LT1256CS:
T = T + (P • 70°C/W)
J A D
T = T + (P • 100°C/W)
J
A
D
4
LT1251/LT1256
U W
TYPICAL PERFORMANCE CHARACTERISTICS
LT1256
Gain vs Control Voltage
LT1251
Gain vs Control Voltage
Spot Input Noise Voltage and
Current vs Frequency
100
10
1
1.0
0.8
0.6
0.4
0.2
0
1.0
0.8
0.6
0.4
0.2
0
–i
n
IN2
IN2
V
= 2.5V
V
= 2.5V
FS
FS
IN1
1.0
IN1
e
n
+i
n
0
0.5
1.5
2.0
2.5
0
0.5
1.0
1.5
2.0
2.5
10
100
1k
10k
FREQUENCY (Hz)
CONTROL VOLTAGE (V)
CONTROL VOLTAGE (V)
1251/56 G06
1251/56 G02
1251/56 G01
LT1251/LT1256
Control Path Bandwidth
Undistorted Output Voltage
vs Frequency
LT1251/LT1256
Control Path Bandwidth
10
8
8
7
6
5
4
3
2
1
10
8
VOLTAGE DRIVE V
C
S
VOLTAGE DRIVE R
C
C
S
A
= 10
V
V
= ±5V
V
V
= GND
= ±5V
6
6
4
4
A
= 1
V
2
2
0
0
PIN 4 NOT IN SOCKET
–2
–4
–6
–8
–10
–2
–4
–6
–8
–10
V
= ±5V
= 1k
S
L
R
R = 1.5k
F
C
V
= V = 2.5V
FS
100k
1M
10M
100M
10k
100k
1M
10M
100M
10k
100k
1M
10M
100M
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
1251/56 G04
1251/56 G05
1251/56 G07
2nd and 3rd Harmonic Distortion
vs Frequency
THD Plus Noise vs Frequency
3rd Order Intercept vs Frequency
–20
–30
–40
–50
–60
–70
50
45
40
35
30
25
20
15
10
10
1
V
A
CC = ±5V
V
A
CC = ±15V
= 1
= 1.5k
= 100Ω
S
V
F
L
O
C
S
V
V
S
A
V
CC = ±5V, V = 1V
IN RMS
= 1
= 1, R = 1.5k, V = 2.5V
F
FS
R = 1.5k
R
R
F
L
C
R
V
V
= 1k
= 2V
V
C
CC = 10%
V
= V = 2.5V
FS
P-P
= V = 2.5V
FS
0.1
V
V
CC = 50%
C
C
3RD
0.01
2ND
CC = 100%
0.001
1
10
100
25
0
5
10
15
20
30
10
100
1k
10k
100k
FREQUENCY (MHz)
FREQUENCY (MHz)
FREQUENCY (Hz)
1251/56 G09
1251/56 G08
1251/56 G10
5
LT1251/LT1256
TYPICAL PERFORMANCE CHARACTERISTICS
U W
Bandwidth vs Feedback
Bandwidth vs Feedback
Voltage Gain and Phase
vs Frequency
Resistance, AV = 1, RL = 100Ω
Resistance, AV = 1, RL = 1k
5
4
45
70
60
50
40
30
20
10
70
60
50
40
30
20
10
PHASE
PEAKING ≤ 0.5dB
PEAKING ≤ 5.0dB
PEAKING ≤ 0.5dB
PEAKING ≤ 5.0dB
0
3
–45
–90
–135
–180
–225
–270
2
V
= ±15V
1
S
V
= ±15V
S
GAIN
0
V
= 5V
V
= 5V
S
S
–1
–2
–3
–4
–5
V
R
R
= ±5V
= 1.3k
= 100Ω
V
S
= ±5V
S
F
L
V
= ±5V
1.2
S
100k
1M
10M
100M
0.6
1.0
1.2
1.4
1.6
1.8
0.6
1.0
1.4
1.6
1.8
0.8
0.8
FEEDBACK RESISTANCE (kΩ)
FEEDBACK RESISTANCE (kΩ)
FREQUENCY (Hz)
1251/56 G13
1251/56 G11
1251/56 G12
Bandwidth vs Feedback
Resistance, AV = 10, RL = 100Ω
Off-Channel Isolation
vs Frequency
Bandwidth vs Feedback
Resistance, AV = 10, RL = 1k
60
50
40
30
20
10
60
50
40
30
20
10
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
PEAKING ≤ 0.5dB
PEAKING ≤ 5.0dB
PEAKING ≤ 0.5dB
PEAKING ≤ 5.0dB
V
V
V
= ±5V
S
= 2.5V
FS
= 0V
= 100Ω
C
R
L
V
= ±15V
R = 1.5k
S
F
A
= 10
V
V
= ±15V
S
V
= 5V
S
V
= 5V
S
A
= 1
V
V
= ±5V
S
V
= ±5V
S
0.4
0.8
1.0
1.2
1.4
1.6
0.4
0.8
1.0
1.2
1.4
1.6
10k
100k
1M
FREQUENCY (Hz)
10M
100M
0.6
0.6
FEEDBACK RESISTANCE (kΩ)
FEEDBACK RESISTANCE (kΩ)
1251/56 G16
1251/56 G14
1251/56 G15
Bandwidth vs Feedback
Resistance, AV = 100, RL = 100Ω
Bandwidth vs Feedback
Resistance, AV = 100, RL = 1k
–3dB Bandwidth vs
Control Voltage
40
35
30
25
20
15
10
10
9
10
9
V
R
V
= ±5V
NO PEAKING
NO PEAKING
S
L
= 100Ω
= 2.5V
V
= ±15V
V
= ±15V
S
FS
S
8
8
R
= 1.3k
F
7
7
V
= ±5V
= 5V
S
V
= ±5V
= 5V
S
6
6
5
5
V
S
V
S
4
4
3
3
2
2
0
0.5
1.0
1.5
2.0
2.5
1.0 1.2 1.4
1.0 1.2 1.4
0.2 0.4 0.6 0.8
1.6 1.8 2.0
0.2 0.4 0.6 0.8
1.6 1.8 2.0
CONTROL VOLTAGE (V)
FEEDBACK RESISTANCE (kΩ)
FEEDBACK RESISTANCE (kΩ)
1251/56 G19
1251/56 G17
1251/56 G18
6
LT1251/LT1256
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs
Full-Scale Voltage
Supply Current vs
Full-Scale Current
Input Common Mode Range
vs Temperature
+
V
14
12
10
8
14
12
10
8
V
= ±5V
V
S
V
C
= ±5V
= 0V
S
INTERNAL RESISTORS
+
T
= 125°C
V
– 1
A
T
= –55°C,
= 25°C
A
A
T
+
V
– 2
+2
T
= –55°C
A
–
T
= 125°C
A
V
6
6
4
4
–
V
+1
2
2
–
0
0
V
0.5
1.0
1.5
2.0
2.5
0
0
300
400
500
100
200
–50 –25
0
25
50
125
75 100
FULL-SCALE CURRENT, I (µA)
FS
FULL-SCALE VOLTAGE, V (V)
TEMPERATURE (°C)
FS
1251/56 G20
1251/56 G21
1251/56 G22
Inverting Input Bias Current
vs Null Voltage
Inverting Input Bias Current
vs Null Voltage
Control and Full-Scale Amp Input
Bias Current vs Input Voltage
200
150
100
50
400
300
–400
–350
–300
–250
–200
–150
–100
–50
V
V
= ±5V
FS
T = –55°C
A
V
S
≥ ±7.5V
V
V
= ±5V
= 2.5V
T
= 25°C
S
S
FS
A
T
= 25°C
A
= 1.25V
T
A
= –55°C
200
T
= –55°C
A
T
A
= 125°C
T
A
= 125°C
T
= 25°C
100
A
0
0
T
A
= 125°C
–50
–100
–150
–200
–100
–200
–300
–400
0
140
160
0
20
40 60 80 100 120
250
–
0
50
100
150
200
300
1
2
4
0
5
3
–
NULL VOLTAGE, REFERENCED TO V (mV)
NULL VOLTAGE, REFERENCED TO V (mV)
INPUT VOLTAGE (V)
1251/56 G24
1251/56 G23
1251/56 G25
Positive Output Saturation
Voltage vs Load Current
Negative Output Saturation
Voltage vs Load Current
Output Short-Circuit Current
vs Temperature
1.7
1.5
1.3
1.1
0.9
0.7
0.5
60
50
40
30
3.0
2.5
2.0
1.5
1.0
0.5
V
S
= ±5V
V
S
= ±5V
T
= 25°C
A
T
= –55°C
A
T
= –55°C
A
T
= 25°C
T
A
= 125°C
A
T
= 125°C
20
A
30
10
40
50
TEMPERATURE (°C)
100 125
0
–30
LOAD CURRENT (mA)
–40
–50 –25
0
25
75
0
–10
–20
LOAD CURRENT (mA)
1251/56 G26
1251/56 G28
1251/56 G27
7
LT1251/LT1256
U W
TYPICAL PERFORMANCE CHARACTERISTICS
Slew Rate vs Full-Scale
Reference Voltage
Power Supply Rejection Ratio
vs Frequency
Slew Rate vs Temperature
80
70
60
50
40
30
20
10
0
350
300
250
200
150
100
50
A
V
= 1
V
= ±5V
= 1
V
A
= ±5V
= 1
S
V
S
V
F
350
300
250
200
A
POSITIVE
NEGATIVE
R = 1.5k
NO LOAD
V
= ±15V
S
V
= V = 2.5V
FS
C
V
= ±5V
S
0
0.5
1.0
1.5
2.0
2.5
–25
0
25
TEMPERATURE (°C)
50
75
125
0
–50
100
1k
10k
100k
FREQUENCY (Hz)
1M
10M
FULL-SCALE REFERENCE VOLTAGE (V)
1251/56 G29
1251/56 G30
1251/56 G31
Settling Time to 10mV
vs Output Step
Settling Time to 1mV
vs Output Step
Output Impedance vs Frequency
10
8
10
8
100
10
V
= ±15V
S
V
R
V
= ±5V
= 1.5k
S
F
R = 1.5k
F
NONINVERTING
6
= V = 2.5V
FS
6
C
INVERTING
4
4
INVERTING,
NONINVERTING
2
2
V
= ±15V
S
0
0
1
R = 1.5k
F
–2
–4
–6
–8
–10
A
= 100
100k
–2
–4
–6
–8
–10
V
INVERTING
A
= 1, 10
1M
NONINVERTING
V
0.1
INVERTING
50
NONINVERTING
0.01
0
100
150
200
0
25
75
100
125
150
50
10k
10M
100M
SETTLING TIME (ns)
SETTLING TIME (ns)
FREQUENCY (Hz)
1251/56 G34
1251/56 G33
1251/56 G32
LT1251
Switching Transient (Glitch)
Differential Gain vs
Controlled Gain
Differential Phase vs
Controlled Gain
1.0
0.5
0
2
1
0
50mV
0
VOUT
–50mV
2.5
VC
0
VFS = 2.5V
R
V
F1 = RF2 = 1.5k
S = ±5V
1251/56 G37
50
60
70
80
90
100
50
60
70
80
90
100
CONTROLLED GAIN, V /V (%)
CONTROLLED GAIN, V /V (%)
C
FS
C
FS
1251/56 G36
1251/56 G35
8
LT1251/LT1256
W
W
SI PLIFIED SCHE ATIC
V
CC
Q10
Q19
Q11
Q8
Q9
Q20
+
+
+
+
I
2
I
1
I
4
I
5
Q16
Q5
Q6
Q17
Q13
Q1
Q7
R2
Q2
Q12
Q18
R1
250Ω
R3
250Ω
R4
250Ω
250Ω
V
FS
Q4
I
C
I
FS
V
C
Q3
Q14
Q15
R
C
5k
R
FS
+
+
5k
I
3
I
6
R
R
C
FS
V
EE
V
CC
Q31
R7
200Ω
R5
200Ω
R6
200Ω
Q30
Q32
Q29
D1
D2
Q54
Q53
Q52
Q38
Q39
Q36 Q37
Q21
Q22
Q56
Q41
Q45
Q47
Q55
Q40
Q44
Q46
OUT
IN1
FB1
IN2
FB2
I
7
Q42
Q57
Q43
Q58
Q25
Q26
Q50
Q51
Q48 Q49
D3
D4
Q59
Q60
R9
Q61
Q33
Q34
R8
200Ω
R11
200Ω
R10
400Ω
Q23
Q24
Q27
Q28
Q35
200Ω
V
EE
1251/56 SS
NULL
9
LT1251/LT1256
U
W U U
APPLICATIONS INFORMATION
Supply Voltage
500mVorthecurrenttolessthan10mA. Ifaveryfastedge
is used to measure settling time with an input step of more
than 6V, the protection circuits will cause the 1mV settling
time to become hundreds of microseconds.
TheLT1251/LT1256arehighspeedamplifiers. Toprevent
problems, use a ground plane with point-to-point wiring
and small bypass capacitors (0.01µF to 0.1µF) at each
supply pin. For good settling characteristics, especially
drivingheavyloads, a4.7µFtantalumwithinaninchortwo
of each supply pin is recommended.
Feedback Resistor Selection
The feedback resistor value determines the bandwidth of
the LT1251/LT1256 as in other current feedback amplifi-
ers. ThecurvesintheTypicalPerformanceCharacteristics
show the effect of the feedback resistor on small-signal
bandwidth for various loads, gains and supply voltages.
The bandwidth is limited at high gains by the 500MHz to
800MHz gain-bandwidth product as shown in the curves.
Capacitance on the inverting input will cause peaking and
increase the bandwidth. Take care to minimize the stray
capacitance on Pins 2 and 13 during printed circuit board
layout for flat response.
The LT1251/LT1256 can be operated on single or split
supplies. The minimum total supply is 4V (Pins 7 to 9).
However, the input common mode range is only guaran-
teed to within 2V of each supply. On a 4V supply the parts
mustbeoperatedintheinvertingmodewiththenoninvert-
ing input biased half way between Pin 7 and Pin 9. See the
Typical Applications section for the proper biasing for
single supply operation.
The op amps in the control section operate from V–
(Pin 7) to within 2V of V+ (Pin 9). For this reason the
positive supply should be 4.5V or greater in order to use
2.5V control and full-scale voltages.
If the two input stages are not operating with equal gain,
the gain versus control voltage characteristic will be
nonlinear. This is true even if RF1 equals RF2. This is
because the open-loop characteristic of a current feed-
back amplifier is dependent on the Thevenin impedance at
the inverting input. For linear control of the gain, the loop
gain of the two stages must be equal. For an extreme
example, let’s take a gain of 101 on input 1, RF1 = 1.5k and
RG1 =15Ω,andunity-gainoninput2,RF2 =1.5k.Thecurve
in Figure 1 shows about 25% error at midscale. To
eliminate this nonlinearity we must change the value of
RF2. The correct value is the Thevenin impedance at
invertinginput1(includingtheinternalresistanceof27Ω)
times the gain set at input 1. For a linear gain versus
control voltage characteristic when input 2 is operating at
unity-gain, the formula is:
Inputs
The noninverting inputs (Pins 1 and 14) are easy to drive
since they look like a 17M resistor in parallel with a 1.5pF
capacitor at most frequencies. However, the input stage
canoscillateatveryhighfrequencies(100MHzto200MHz)
if the source impedance is inductive (like an unterminated
cable). Several inches of wire look inductive at these high
frequencies and can cause oscillations. Check for oscilla-
tions at the inverting inputs (Pins 2 and 13) with a 10×
probe and a 200MHz oscilloscope. A small capacitor
(10pF to 50pF) from the input to ground or a small resistor
(100Ω to 300Ω) in series with the input will stop these
parasitic oscillations, even when the source is inductive.
These components must be within an inch of the IC in
order to be effective.
RF2 = (AV1)(RF1 R G1 + 27)
RF2 = (101)(14.85 + 27) = 4227
All of the inputs to the LT1251/LT1256 have ESD protec-
tion circuits. During normal operation these circuits have
no effect. If the voltage between the noninverting and
inverting inputs exceeds 6V, the protection circuits will
trigger and attempt to short the inputs together. This
condition will continue until the voltage drops to less than
Because the feedback resistor of the unity-gain input is
increased, the bandwidth will be lower and the output
noise will be higher. We can improve this situation by
reducing the values of RF1 and RG1, but at high gains the
internal 27Ω dominates.
10
LT1251/LT1256
U
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APPLICATIONS INFORMATION
100
millivolts of the negative supply can drive the NULL pin.
The AM modulator application shows an LT1077 driving
the NULL pin to eliminate the output DC offset voltage.
V
= 2.5V
FS
Crosstalk
R
= 4.3k
F2
50
The amount of signal from the off input that appears at the
output is a function of frequency and the circuit topology.
The nature of a current feedback input stage is to force the
voltage at the inverting input to be equal to the voltage at
the noninverting input. This is independent of feedback
and forced by a buffer amplifier between the inputs. When
the LT1251/LT1256 are operating noninverting, the off
inputsignalispresentattheinvertinginput. Sinceoneend
of the feedback resistor is connected to this input, the off
signal is only a feedback resistor away from the output.
The amount of unwanted signal at the output is deter-
mined by the size of the feedback resistor and the output
impedance of the LT1251/LT1256. The output impedance
riseswithincreasingfrequencyresultinginmorecrosstalk
at higher frequencies. Additionally, the current that flows
in the inverting input is diverted to the supplies within the
chip and some of this signal will also show up at the
output. With a 1.5k feedback resistor, the crosstalk is
down about 86dB at low frequencies and rises to –78dB
at 1MHz and on to –60dB at 6MHz. The curves show the
details.
R
= 1.5k
F2
0
0
0.5
1.0
1.5
2.0
2.5
CONTROL VOLTAGE (V)
1251/56 F01
Figure 1. Linear Gain Control from 0 to 101
Capacitive Loads
Increasing the value of the feedback resistor reduces the
bandwidth and open-loop gain of the LT1251/LT1256;
therefore, the pole introduced by a capacitive load can be
overcome. If there is little or no resistive load in parallel
with the load capacitance, the output stage will resonate,
peak and possibly oscillate. With a resistive load of 150Ω,
any capacitive load can be accommodated by increasing
the feedback resistor. If the capacitive load cannot be
paralleled with a DC load of 150Ω, a network of 200pF in
series with 100Ω should be placed from the output to
ground. Then the feedback resistor should be selected for
best response.
Distortion
Whenonlyoneinputiscontributingtotheoutput(VC =0%
or100%)the LT1251/LT1256have very lowdistortion. As
thecontrolreducestheoutput, thedistortionwillincrease.
The amount of increase is a function of the current that
flows in the inverting input. Larger input signals generate
more distortion. Using a larger feedback resistor will
reduce the distortion at the expense of higher output
noise.
The Null Pin
Pin 6 can be used to adjust the gain of an internal current
mirror to change the output offset. The open circuit
voltage at Pin 6 is set by the full scale current IFS flowing
through200Ω tothenegativesupply. Therefore, theNULL
pin sits 100mV above the negative supply with VFS equal
to 2.5V. Any op amp whose output swings within a few
11
LT1251/LT1256
U
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APPLICATIONS INFORMATION
Signal Path Description
R
R
F1
G1
I
1
R
1
2
–
I
1
1
2
K
1
+
V
1
I
8
O
V
O
+1
Σ
14
C
R
OL
V
2
+
–
I
2
1 – K
13
R
2
I
2
R
F2
R
G2
1251/56 BD
Figure 2. Signal Path Block Diagram
V
V
O
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.
2
I =
−
2
R
R
R
F2
(
)(
)
G2 F2
R +R
+1
F2
2
R +
2
R
G
2
R
+R
G
2
F
2
I = KI + 1−K I
(
)
Each input stage has a unity-gain buffer from the nonin-
vertinginputtotheinvertinginput.Therefore,theinverting
input is at the same voltage as the noninverting input. R1
and R2 represent the internal output resistances of these
buffers, approximately 27Ω.
O
1
2
R
OL
V =I
O
O
1+ sR C
(
)
OL
Substituting and rearranging gives:
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.
1−K V
(
)
2
KV
1
+
By inspection of the diagram:
R
(
R
R
R
)(
)
(
)(
)
G1 F1
G2 F2
R +
R +
2
1
R +R
R
+R
G1
F1
G2
F2
V
V
O
V =
1
O
I =
−
1
1−K
(
)
1+ sR C
K
R
R
R
F1
OL
(
)(
)
G1 F1
+
+
R +R
+1
F1
1
R +
1
R
R
R
R
OL
F1
F2
G1
R +R
R +R
+1 R +R
+1
G1
F1
F1
1
F2
2
R
R
G2
G1
General Equation for the Noninverting Amplifier Case
12
LT1251/LT1256
U
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APPLICATIONS INFORMATION
Similarly for the inverting case where the noninverting
inputsaregroundedandtheinputvoltagesV1 andV2 drive
the normally grounded ends of RG1 and RG2, we get:
In low gain applications, R1 and R2 are small compared to
the feedback resistors and therefore we can simplify the
equation to:
1−K V
(
)
2
KV
1
+
1−K V
(
)
2
KV
1
R
R
R
R
F2
+
G1
G2
R +R
+1
R
+R
+1
G1
1
G2
2
R
R
R
R
(
)(
)
(
)(
)
G1 F1
G2 F2
F1
V = −
O
R +R
R +R
1−K
(
)
G1
F1
G2
F2
1+ sR C
K
OL
V =
O
+
+
1−K
R
R
R
R
(
)
1+ sR C
K
OL
F1
F2
OL
R +R
+1 R +R
+1
+
+
F1
1
F2
2
R
G2
R
R
R
F2
G1
OL
F1
General Equation for the Inverting Amplifier Case
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 RF1 and RF2. A 1% mis-
match in the feedback resistors results in a 0.25% error at
K = 0.5.
Note that the denominator is the same as the noninverting
case. In low gain applications, R1 and R2 are small
compared to the feedback resistors and therefore we can
simplify the equation to:
If we set RF1 = RF2 and assume ROL >> RF1 (a 0.1% error
at low frequencies) the above equation simplifies to:
1−K V
(
)
2
KV
1
+
V =KV A + 1−K V A
R
R
K
(
)
O
1 V1
2 V2
G1
G2
V = −
O
1−K
(
)
R
R
R
1+ sR C
F1
F2
OL
where A = 1+
and A = 1+
+
+
V1
V2
R
R
R
R
F2
G1
G2
OL
F1
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.
Again, if we set RF1 = RF2 and assume ROL >> RF1 (a 0.1%
error at low frequencies) the above equation simplifies to:
V = − KV A + 1−K V A
If only one input is used (for example, V1) and Pin 14 is
grounded, then the gain is proportional to K.
(
)
O
1 V1
2 V2
[
]
R
R
R
F1
F2
where A =
and A
=
V2
V1
R
V
G1
G2
O
= KA
V1
V
1
The 4-resistor difference amplifier yields the same result
as the inverting amplifier case, and the common mode
rejection is independent of K.
13
LT1251/LT1256
U
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APPLICATIONS INFORMATION
gain) is ±3% as detailed in the electrical tables. By using
a 2.5V full-scale voltage and the internal resistors, no
additional errors need be accounted for.
Control Circuit Description
+
V
In the LT1256, K changes linearly with IC. To insure that K
is zero, VC must be negative 15mV or more to overcome
the worst-case control op amp offset. Similarly to insure
that K is 100%, VC must be 3% larger than VFS based on
the guaranteed gain accuracy.
I
I
C
FS
12
3
+
–
+
–
V
I
V
I
C
FS
C
FS
To eliminate the overdrive requirement, the LT1251 has
internal circuitry that senses when the control current is at
about 5% and sets K to 0%. Similarly, at about 95% it sets
K to 100%. The LT1251 guarantees that a 2% (50mV)
input gives zero and 98% (2.45V) gives 100%.
11
10
4
5
C
FS
R
R
FS
5k
C
5k
R
C
R
FS
CONTROL V TO I
FULL SCALE V TO I
1251/56 F03
The operating currents of the LT1251/LT1256 are derived
from IFS and therefore the quiescent current is a function
of VFS and RFS. The electrical tables show the supply
current for three values of VFS including zero. An approxi-
mate formula for the supply current is:
Figure 3. Control Circuit Block Diagram
The control section of the LT1251/LT1256 consists of two
identical voltage-to-current converters (V-to-I); each
V-to-I contains an op amp, an NPN transistor and a
resistor. The converter on the right generates a full-scale
current IFS and the one on the left generates a control
current IC. The ratio IC/IFS is called K. K goes from a
minimum of zero (when IC is zero) to a maximum of one
(when IC is equal to, or greater than, IFS). K determines the
gain from each signal input to the output.
IS = 1mA + (24)(IFS) + (VS/20k)
where VS is the total supply voltage between Pins 9 and 7.
By reducing IFS the supply current can be reduced, how-
ever, the slew rate and bandwidth will also be reduced as
indicated in the characteristic curves. Using the internal
resistors (5k) with VFS equal to 2.5V results in IFS equal to
500µA; there is no reason to use a larger value of IFS.
The op amp in each V-to-I drives the transistor until the
voltage at the inverting input is the same as the voltage at
the noninverting input. If the open end of the resistor (Pin
5 or 10) is grounded, the voltage across the resistor is the
same as the voltage at the noninverting input. The emitter
currentisthereforeequaltotheinputvoltageVC dividedby
the resistor value RC. The collector current is essentially
the same as the emitter current and it is the ratio of the two
collector currents that sets the gain.
The inverting inputs of the V-to-I converters are available
so that external resistors can be used instead of the
internal ones. For example, if a 10V full-scale voltage is
desired, anexternalpairof20kresistorsshouldbeusedto
set IFS to 500µA. The positive supply voltage must be 2.5V
greater than the maximum VC and/or VFS to keep the
transistors from saturating. Do not use the internal resis-
tors with external resistors because the internal resistors
have a large positive temperature coefficient (0.2%/°C)
that will cause gain errors.
TheLT1251/LT1256aretestedwithPins5and10grounded
andafull-scalevoltageof2.5VappliedtoVFS (Pin12).This
sets IFS at approximately 500µA; the control voltage VC is
applied to Pin 3. When the control voltage is negative or
zero, IC is zero and K is zero. When VC is 2.5V or greater,
IC is equal to or greater than IFS and K is one. The gain of
channel one goes from 0% to 100% as VC goes from zero
to 2.5V. The gain of channel two goes the opposite way,
from 100% down to 0%. The worst-case error in K (the
If the control voltage is applied to the free end of resistor
RC (Pin5)andtheVC input(Pin3)isgrounded,thepolarity
of the control voltage must be inverted. Therefore, K will
be 0% for zero input and 100% for –2.5V input, assuming
VFS equals 2.5V. With Pin 3 grounded, Pin 4 is a virtual
ground; this is convenient for summing several negative
going control signals.
14
LT1251/LT1256
U
TYPICAL APPLICATIONS
AM Modulator with DC Output Nulling Circuit
0.1µF
LT1256
1
14
13
12
11
10
9
1MHz
CARRIER
+
–
+
–
1
2
50Ω
2
CONTROL
220k
3
2.5VDC
INPUT
+
–
+
–
I
FS
I
0.1µF
C
FS
5k
C
4
5
AUDIO
MODULATION
R
R
F1
1.5k
F2
1.5k
5k
220k
NULL 6
+
V
7
8
–
V
OUT
V
220k
+
V
0.1µF
–
LT1077
+
1251/56 TA03
–
V
Single Supply Noninverting AC Amplifier
with Digital Gain Control
Single Supply Inverting AC Amplifier
C1
10µF
R
R
G1
F1
1.5k
R
G1
1.5k
R
F1
1.5k
1.5k
10µF
+
V1
+
LT1251/LT1256
2
1
LT1251/LT1256
R1
20k
–
+
2
1
1
–
+
+
V
1
10µF
8
9
7
+
V1
R2
C
V
OUT
O
8
9
7
+
14
13
V
OUT
20k
10µF
+
–
+
–
V
V
5V
10µF
14
13
+
–
2
+
–
V
V
5V
V2
5V
+
20k
2
10k
10k
V
C
R
R
V
FS
C
FS
V
C
R
C
R
FS
V
FS
3
5
10 12
+
3
5
10 12
20k
10µF
2.5VDC
INPUT
CONTROL
VOLTAGE
C2
10µF
R
R
1.5k
F2
10µF
G2
1.5k
+
+
V2
R
R
1251/56 TA05
G2
F2
1.5k
1.5k
V
REF
D
IN
CLK
µP
LTC1257
V
OUT
LOAD
GND
V
CC
1251/56 TA06
5V
15
LT1251/LT1256
TYPICAL APPLICATIONS
U
Controlled Gain, Voltage-to-Current Converter
(Current Source)
R
F
1k
R
F
1k
R
G
100Ω
LT1256
× 4
1
2
+
–
1
2
R
O
V
IN
1k
8
I
OUT
14
13
+
–
+
LT1363
V
C
R
R
V
FS
C
FS
3
5
10 12
–
2.5VDC
INPUT
CONTROL
VOLTAGE
R
1k
F
R
F
1k
1251/56 TA09
V
R
R
R
V
OUTPUT RESISTANCE DEPENDS
ON MATCHING OF RESISTORS
IN
F
C
I
=
OUT
(
)
V
O
G
FS
Variable Lowpass, Highpass and Allpass Filter
R2
R1
R3
–
V
IN
INVERTED
HIGHPASS
LT1252
BASIC VARIABLE INTEGRATOR
+
R
R
R
C
ALLPASS
1.5k
R4
LT1256
2
1
–
+
1
2
R1 R3
=
8
R2 R4
LOWPASS
14
13
+
–
V
C
R
C
R
FS
V
FS
3
5
10 12
1.5k
V
FS
V
C
R
C
R
DC
10k
1251/56 TA13
16
LT1251/LT1256
U
TYPICAL APPLICATIONS
Logarithmic Gain Control (Noninverting)
6k
15
V
= 2.5V
FS
LT1251/LT1256
2k
2
1
–
+
1
V
IN
8
V
OUT
600Ω
200Ω
9
7
14
13
+
–
V
V
+
–
0
2
V
R
C
R
V
FS
C
FS
3
5
10 12
<1dB ERROR
2.5VDC
INPUT
CONTROL
VOLTAGE
V
C
1.5k
A
V
= 24dB
– 0.5
(
)
V
FS
1251/56 TA07a
–15
0
1.25
2.5
CONTROL VOLTAGE (V)
1251/56 TA07b
Logarithmic Gain Control (Inverting)
6k
15
V
= 2.5V
FS
LT1251/LT1256
1.5k
6k
2
1
–
+
1
8
9
7
V
OUT
V
IN
14
13
+
–
+
–
V
V
0
2
V
R
R
V
FS
C
C
FS
<1dB ERROR
3
5
10 12
V
CONTROL
VOLTAGE
2.5VDC
INPUT
C
A
= 24dB
– 0.5
V
(
)
1.5k
V
FS
–15
1251/56 TA08a
0
1.25
2.5
CONTROL VOLTAGE (V)
1251/56 TA08b
1MHz Wien Bridge Oscillator
Basic Variable Integrator
C
R
V
IN
1.5k
1k
LT1251/LT1256
LT1256
1
2
2
–
+
–
200Ω
1
1
1
+
50Ω
8
8
V
OUT
V
OUT
14
13
14
13
+
–
+
–
200Ω
100pF
1.6k
100pF
2
2
1.6k
V
R
R
V
FS
10 12
C
C
FS
V
R
R
V
FS
10 12
C
C
FS
3
5
3
5
2.5VDC
INPUT
1.5k
V
V
5V
1
FS
C
1k
R
C
2
+
10µF
10k
7
LT1116
–1
R
10k
+
DC
T(s) =
3
–
V
V
1k
FS
(s)(R)(C)
5, 4, 6
(
)
C
THE TIME CONSTANT IS INVERSELY PROPORTIONAL TO V .
C
R
IS REQUIRED TO DEFINE THE DC OUTPUT WHEN
DC
1251/56 TA11
1251/56 TA12
THE CONTROL IS AT ZERO.
17
LT1251/LT1256
U
TYPICAL APPLICATIONS
3.58MHz Phase Shifter
R2
1k
R'2
1k
C1
0.001µF
C'1
R1
470Ω
0.001µF
R5
R6
R'5
R'6
V
IN
–
–
430Ω
430Ω
430Ω
430Ω
1/2
LT1253
1/2
LT1253
R3
470Ω
C5
50pF
C'5
50pF
R7
150Ω
R'7
R8
910Ω
R'8
C2
100pF
C'2
+
+
150Ω
R'3
910Ω
100pF
470Ω
R9
1.5k
R'9
1.5k
LT1256
LT1256
1
2
1
2
+
–
+
–
1
2
1
2
8
8
14
13
14
13
+
–
+
–
R4
1k
R'4
1k
V
C
R
R
V
V
R
R
V
FS
C
FS
FS
C
C
FS
3
5
10 12
3
5
10 12
R10
1.5k
R'10
1.5k
2.5V
C3, 100pF
2.5V
C'3, 100pF
V
V
C
C
R11
150Ω
R'11
150Ω
R12, 10k
R'12, 10k
C4
0.002µF
C'4
0.002µF
R''2
1k
C''1
0.001µF
R''5
R''6
–
1000pF
430Ω
430Ω
1/2
LT1253
+
75Ω
1/2
LT1253
C''5
R''7
R''8
C''2
10k
V
OUT
+
50pF
150Ω
R''3
910Ω
100pF
–
470Ω
1k
R''9
1.5k
LT1256
1
2
+
–
1k
1
2
8
1.00
0.98
0.96
0.94
14
13
420
360
300
240
180
120
60
+
–
R''4
1k
GAIN
V
R
R
V
FS
10 12
C
3
C
FS
5
PHASE
R''10
1.5k
V
2.5V
C
C''3, 100pF
R''12, 10k
R''11
150Ω
0
C''4
0.002µF
1251/56 TA14a
0
0.5
1.0
1.5
2.0
2.5
CONTROL VOLTAGE, V (V)
C
1251/56 TA14b
18
LT1251/LT1256
U
TYPICAL APPLICATIONS
State Variable Filter with Adjustable Frequency and Q
1k
1k
HP
1k
OUT
1k
V
–
+
500pF
IN
LT1252
BP
OUT
1.5k
LT1256
2
1
–
+
1
2
500pF
1k
8
14
+
–
1.5k
LT1256
13
2
1
–
+
500Ω
1
2
V
R
C
R
V
FS
10 12
C
3
FS
8
5
1.5k
LP
OUT
14
V
FS
Vω
+
–
1k
13
500pF
V
C
R
C
R
FS
V
FS
1.5k
3
5
10 12
1.5k
1.5k
V
FS
Vω
LT1256
2
–
500pF
1
1251/56 TA15a
1
1k
+
8
14
+
2
13
–
V
V
R
R
C
V
V
FS
FS
C
3
V
FS
= 2.5V
12 10
5
FS
Q
1.5k
Center Frequency vs Control Voltage Vω
Q vs Control Voltage VQ
6
5
4
3
2
1
0
350
V
= 2.5V
V
= 2.5V
FS
FS
300
250
200
150
100
50
0
0
0.5
1.0
1.5
(V)
2.0
2.5
0.5
1.0
Vω (V)
1.5
2.0
2.5
0
V
Q
1251/56 TA15c
1251/56 TA15b
19
LT1251/LT1256
W
W
ACRO ODEL
For PSpiceTM
*
* Linear Technology LT1251/LT1256 VIDEO FADER MACROMODEL
* Written: 3-11-1994 BY WILLIAM H. GROSS.
* Corrected: 7-15-1996
* Connections: as per datasheet pinout
*1=first noninverting input
*2=first inverting input
*3=control voltage input
*4=control current input
*5=control resistor, RC
*6=null input
*7=negative supply
*8=output
*9=positive supply
*10=full scale resistor, RFS
*11=full scale current input
*12=full scale voltage input
*13=second inverting input
*14=second noninverting input
*
.SUBCKT LT1251 1 2 3 4 5 6 7 8 9 10 11 12 13 14
*
*first input stage
IB1
RI1
C1
1
1
1
0
0
0
500NA
17MEG
1.5PF
E1
VOS1
R1
2A
2A
2B
2
0
2B
2
VALUE={LIMIT (V(1), V(8N)+0.4, V(8P)–0.4)+V(EN)/30}
2.5MV
27
C2
0
1PF
*
*second input stage
IB2
RI2
C14
E2
14
14
14
13A
13A
13B
13
0
0
0
450NA
17MEG
1.5PF
0
VALUE={LIMIT (V(14), V(8N)+0.4, V(8P)–0.4)+V(EN)/30}
1.5MV
27
VOS2
R2
13B
13
0
C13
*
1PF
*control amp
IBC
RIC
C3
3
3
3
0
0
0
–300NA
100MEG
1PF
R3
CBWC
EC
VOSC
C4
RC
3
3A
0
0
4
0
1600
10PF
3A
5MV
1PF
5K
3A
3B
3B
4
0
1.0
4
5
C5
5
0
1PF
*
PSpice is a trademark of MicroSim Corporation
20
LT1251/LT1256
W
W
ACRO ODEL
*full scale amp
IBFS
RIFS
C12
12
12
12
12
0
0
0
–300NA
100MEG
1PF
1600
10PF
12A
–5MV
1PF
5K
R12
12A
0
CBWFS 12A
EFS 12B
VOSFS 12B
C11
RFS
C10
*
0
0
1.0
11
0
11
11
10
10
0
1PF
*generating K
*** the next two lines are for the LT1251
EK K 0 TABLE {I(VOSC)/I(VOSFS)}= (–100,0)
(0.04,0)
(0.1,0.11)
+
(0.9,0.907)(0.95,1.0) (100,1.0)
*** the next two lines are for the LT1256
*EK K 0 TABLE {I(VOSC)/I(VOSFS)}= (–100,0)
*+
(0,0)
(0.2,0.21)
(100,1.0)
(0.9,0.9)
(1.0,1.0)
RDUMMY
RNOISE1 EN
RNOISE2 EN
K
0
0
0
1MEG
200K
200K
*generates 40.7nV/rtHz
*
*null circuit
GNULL
RN1
VNULL
RN2
C6
7
6A
6A
6B
6
6A
7
6B
6
VALUE={I(VOSFS)}
200
0.0V
400
1PF
7
*
*output stage
E6 8A
0
+VALUE={1.8MEG*(I(VOS1)*V(K)+I(VOS2)*(1–V(K))–I(VNULL)+0.10UA+0.0007*V(EN))}
RG
CG
E8
V8
R8
*
8A
8B
8C
8C
8D
8B
0
0
8D
8
1.8MEG
3.4PF
8B
0.0V
11
0
1.0
*output swing and current limit
DP
VDP
DN
VDN
.MODEL
GCL
*
8B
8P
8N
8N
D1
8B
8P
9
8B
7
D
0
D1
–1.4V
D1
1.4V
TABLE {I(V8)}=(–1,–1)(–0.04,0)(0.04,0)(1,1)
*supply current
GQ
9
9
7
7
0
0
VALUE={1MA+24*I(VOSFS)+(V(7)–V(9))/20K}
TABLE {I(V8)}=(–1,0)(0,0)(1,1)
TABLE {I(V8)}=(–1,–1)(0,0)(1,0)
GCC
GEE
*
.ENDS LT1251
21
LT1251/LT1256
W
W
ACRO ODEL
LT1251/LT1256 Macro Model for PSpice
PIN # IN
NODE # IN
K GENERATOR
NOISE GENERATOR
FIRST INPUT STAGE
R1
27Ω
2
V
OS1
2A
K
EN
1
I
RI
C1
1.5pF
B1
C2
1pF
1
2B
R
R
R
NOISE2
200k
E1
DUMMY
NOISE1
500nA
E
K
17M
1M
200k
NULL CIRCUIT
SECOND INPUT STAGE
R2
27Ω
13
V
OS2
R
13A
N2
V
NULL
6A
400Ω
14
6
I
RI
C13
1pF
C14
1.5pF
B2
2
13B
E2
R
450nA
N1
17M
6B
C6
G
NULL
200Ω
1pF
7
CONTROL AMP
SUPPLY CURRENTS
R3
1.6k
R
C
4
V
OSC
3A
3B
5k
3
9
7
5
9
7
I
RI
C
C3
1pF
C
BWC
10pF
BC
C4
1pF
C5
1pF
E
C
G
Q
G
EE
G
–300nA
100M
CC
1251/56 MM
FULL SCALE AMP
R12
1.6k
11
R
FS
5k
V
OSFS
12A
12B
12
10
I
RI
FS
100M
C12
1pF
C
BWFS
10pF
BFS
C11
1pF
C10
1pF
E
FS
–300nA
OUTPUT STAGE AND VOLTAGE SWING/CURRENT LIMIT
R8
11Ω
R
G
V8
8D
8B
8A
8C
1.8M
8
D
D
N
P
C
G
8P
8N
3.4pF
V
DP
V
DN
G
E6
E8
CL
9
7
22
LT1251/LT1256
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
N Package
14-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.770*
(19.558)
MAX
0.300 – 0.325
(7.620 – 8.255)
0.045 – 0.065
(1.143 – 1.651)
0.130 ± 0.005
(3.302 ± 0.127)
14
13
12
11
10
9
8
0.015
(0.380)
MIN
0.255 ± 0.015*
(6.477 ± 0.381)
0.065
(1.651)
TYP
0.009 – 0.015
(0.229 – 0.381)
+0.025
1
2
3
5
6
7
4
0.325
0.005
(0.125)
MIN
0.100 ± 0.010
(2.540 ± 0.254)
–0.015
0.125
(3.175)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
+0.635
8.255
(
)
–0.381
N14 0695
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
S Package
14-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.337 – 0.344*
(8.560 – 8.738)
14
13
12
11
10
9
8
0.010 – 0.020
(0.254 – 0.508)
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0° – 8° TYP
0.228 – 0.244
0.150 – 0.157**
(5.791 – 6.197)
(3.810 – 3.988)
0.050
(1.270)
TYP
0.014 – 0.019
(0.355 – 0.483)
0.016 – 0.050
0.406 – 1.270
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
1
2
3
4
5
6
7
S14 0695
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
23
LT1251/LT1256
U
TYPICAL APPLICATIONS
4-Quadrant Multiplier as a Double-Sideband Suppressed-Carrier Modulator
Modulation Gain vs Control Voltage
1.0
0.8
V
V
= ±5V
FS
S
= 2.5V
LT1256
1
2
3
4
5
6
7
14
13
12
11
10
9
0.6
+
–
+
–
R
G1
1
0.4
2
1.5k
MODULATION
0.2
CONTROL
1MHz
CARRIER
0
+
–
+
–
I
FS
I
C
FS
5k
C
–0.2
–0.4
–0.6
–0.8
–1.0
0.1µF
10k*
R
R
F1
1.5k
F2
1.5k
5k
+
V
10k
8
–
0
0.5
1.0
1.5
2.0
2.5
V
CONTROL VOLTAGE, PIN 3 (V)
V
OUT
2.5VDC
INPUT
1251/56 TA04b
1251/56 TA04a
0.1µF
*TRIM FOR SYMMETRY
Soft Clipper
1.5k
VIN
LT1256
2
1
–
+
1
2
8
V
OUT
9
+
14
13
+
–
V
V
IN
7
–
V
VOUT
V
R
R
V
FS
C
C
FS
3
5
10 12
2.5VDC
INPUT
1N914
1N914
VFS = 2.5V
S = ±5V
f = 1kHz
V
200pF
5k 1k
1251/56 TA10b
1.5k
1251/56 TA10a
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1228
100MHz Current Feedback Amplifier with DC Gain Control
Low Cost Video Amplifier
Includes a 75MHz Transconductance Amplifier
100MHz Bandwidth
LT1252
LT1253/LT1254
LT1259/LT1260
Low Cost Dual and Quad Video Amplifiers
90 MHz Bandwidth
Low Cost Dual and Triple 130MHz Current Feedback
Amplifiers with Shutdown
Makes Fast Video MUX
LT/GP 0896 REV A 5K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1994
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
24
●
●
(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
相关型号：
LT1259CN14
IC DUAL OP-AMP, 10000 uV OFFSET-MAX, 130 MHz BAND WIDTH, PDIP14, Operational Amplifier
Linear
LT1259CS#PBF
LT1259 - Low Cost Dual and Triple 130MHz Current Feedback Amplifiers with Shutdown; Package: SO; Pins: 14; Temperature Range: 0°C to 70°C
Linear
LT1259CS#TRPBF
LT1259 - Low Cost Dual and Triple 130MHz Current Feedback Amplifiers with Shutdown; Package: SO; Pins: 14; Temperature Range: 0°C to 70°C
Linear
LT1259CS14
IC DUAL OP-AMP, 10000 uV OFFSET-MAX, 130 MHz BAND WIDTH, PDSO14, Operational Amplifier
Linear
LT1259IN#PBF
LT1259 - Low Cost Dual and Triple 130MHz Current Feedback Amplifiers with Shutdown; Package: PDIP; Pins: 14; Temperature Range: -40°C to 85°C
Linear
LT1259IS#PBF
LT1259 - Low Cost Dual and Triple 130MHz Current Feedback Amplifiers with Shutdown; Package: SO; Pins: 14; Temperature Range: -40°C to 85°C
Linear
LT1259IS#TRPBF
LT1259 - Low Cost Dual and Triple 130MHz Current Feedback Amplifiers with Shutdown; Package: SO; Pins: 14; Temperature Range: -40°C to 85°C
Linear
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