LT1227
140MHz Video Current
Feedback Amplifier
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FEATURES
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DESCRIPTIO
140MHz Bandwidth: AV = 2, RL = 150Ω
1100V/µs Slew Rate
Low Cost
30mA Output Drive Current
0.01% Differential Gain
0.01° Differential Phase
High Input Impedance: 14MΩ, 3pF
Wide Supply Range: ±2V to ±15V
Shutdown Mode: IS < 250µA
Low Supply Current: IS = 10mA
Inputs Common Mode to Within 1.5V of Supplies
Outputs Swing Within 0.8V of Supplies
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Video Amplifiers
Cable Drivers
RGB Amplifiers
Test Equipment Amplifiers
50Ω Buffers for Driving Mixers
The LT1227 is manufactured on Linear Technology’s
proprietary complementary bipolar process.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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A shutdown feature switches the device into a high impedance, low current mode, allowing multiple devices to be
connected in parallel and selected. Input to output isolation in shutdown is 70dB at 10MHz for input amplitudes up
to 10VP-P. The shutdown pin interfaces to open collector
or open drain logic and takes only 4µs to enable or disable.
The LT1227 comes in the industry standard pinout and
can upgrade the performance of many older products. For
a dual or quad version, see the LT1229/1230 data sheet.
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APPLICATIO S
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The LT®1227 is a current feedback amplifier with wide
bandwidth and excellent video characteristics. The low
differential gain and phase, wide bandwidth, and 30mA
output drive current make the LT1227 well suited to drive
cables in video systems.
TYPICAL APPLICATIO
Video Cable Driver
Differential Gain and Phase
vs Supply Voltage
0.20
+
75Ω
LT1227
75Ω
CABLE
RF
1k
VOUT
VOUT
=1
VIN
75Ω
0.16
0.16
0.12
0.12
0.08
0.08
∆φ
DIFFERENTIAL GAIN (%)
–
RG
1k
0.20
NTSC COMPOSITE
f = 3.58MHz
DIFFERENTIAL PHASE (DEG)
VIN
0.04
0.04
1227 TA01
∆G
0
5
7
11
13
9
SUPPLY VOLTAGE (±V)
15
0
LT1227 • TA02
1
LT1227
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RATI GS
W
W W
W
AXI U
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ABSOLUTE
PACKAGE/ORDER I FOR ATIO
(Note 1)
Supply Voltage ..................................................... ±18V
Input Current ...................................................... ±15mA
Output Short Circuit Duration (Note 2) ........ Continuous
Operating Temperature Range
LT1227C .................................................. 0°C to 70°C
LT1227M (OBSOLETE) .................... – 55°C to 125°C
Storage Temperature Range ................. – 65°C to 150°C
Junction Temperature
Plastic Package ................................................ 150°C
Ceramic Package (OBSOLETE) ........................ 175°C
Lead Temperature (Soldering, 10 sec.)................ 300°C
ORDER PART
NUMBER
TOP VIEW
NULL 1
8 SHDN
LT1227CN8
–IN 2
7 V+
+IN 3
6 OUT
V– 4
5 NULL
N8 PACKAGE
8-LEAD PLASTIC DIP
TJMAX = 150°C, θJA = 100°C/W (N)
J8 PACKAGE
8-LEAD CERAMIC DIP
TJMAX = 175°C, θJA = 100°C/W (J)
LT1227MJ8
OBSOLETE PACKAGE
Consider the N8 Package for Alternate Source.
ORDER PART
NUMBER
TOP VIEW
NULL 1
8 SHDN
–IN 2
7 V+
+IN 3
6
V– 4
LT1227CS8
OUT
5 NULL
S8 PART MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 150°C, θJA = 150°C/W
1227
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCM = 0, ±5V ≤ VS ≤ ±15V, pulse tested, unless otherwise noted.
SYMBOL
VOS
PARAMETER
Input Offset Voltage
IIN+
Input Offset Voltage Drift
Noninverting Input Current
CONDITIONS
TA = 25°C
MIN
TYP
±3
●
10
±0.3
●
TA = 25°C
●
IIN–
Inverting Input Current
±10
TA = 25°C
●
en
+in
–in
RIN
Input Noise Voltage Density
Noninverting Input Noise Current Density
Inverting Input Noise Current Density
Input Resistance
CIN
Input Capacitance
Input Voltage Range
f = 1kHz, RF = 1k, RG = 10Ω, RS = 0Ω
f = 1kHz
f = 1kHz
VIN = ±13V, VS = ±15V
VIN = ±3V, VS = ±5V
●
●
VS = ±15V, TA = 25°C
●
VS = ±5V, TA = 25°C
●
CMRR
2
Common Mode Rejection Ratio
VS = ±15V, VCM = ±13V, TA = 25°C
VS = ±15V, VCM = ±12V
VS = ±5V, VCM = ±3V, TA = 25°C
VS = ±5V, VCM = ±2V
●
●
1.5
1.5
±13
±12
±3
±2
55
55
55
55
3.2
1.7
32
14
11
3
±13.5
±3.5
62
61
MAX
±10
±15
±3
±10
±60
±100
UNITS
mV
mV
µV/°C
µA
µA
µA
µA
nV/√Hz
pA/√Hz
pA/√Hz
MΩ
MΩ
pF
V
V
V
V
dB
dB
dB
dB
LT1227
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCM = 0, ±5V ≤ VS ≤ ±15V, pulse tested, unless otherwise noted.
SYMBOL
PSRR
PARAMETER
Inverting Input Current
Common Mode Rejection
Power Supply Rejection Ratio
AV
Noninverting Input Current
Power Supply Rejection
Inverting Input Current
Power Supply Rejection
Large-Signal Voltage Gain
ROL
Transresistance, ∆VOUT/∆IIN–
VOUT
Maximum Output Voltage Swing
CONDITIONS
VS = ±15V, VCM = ±13V, TA = 25°C
VS = ±15V, VCM = ±12V
VS = ±5V, VCM = ±3V, TA = 25°C
VS = ±5V, VCM = ±2V
VS = ±2V to ±15V, TA = 25°C
VS = ±3V to ±15V
VS = ±2V to ±15V, TA = 25°C
VS = ±3V to ±15V
VS = ±2V to ±15V, TA = 25°C
VS = ±3V to ±15V
VS = ±15V, VOUT = ±10V, RL = 1k
VS = ±5V, VOUT = ±2V, RL = 150Ω
VS = ±15V, VOUT = ±10V, RL = 1k
VS = ±5V, VOUT = ±2V, RL = 150Ω
VS = ±15V, RL = 400Ω, TA = 25°C
MIN
●
4.5
●
●
0.25
●
●
●
●
●
●
RL = 0Ω, TA = 25°C
VS = ±15V, VOUT = 0V, TA = 25°C
55
55
100
100
±12
±10
±3
±2.5
30
VS = ±15V, Pin 8 Voltage = 0V, TA = 25°C
±3.7
60
10
120
●
I8
SR
tr, tf
BW
tr, tf
tS
Shutdown Pin Current (Note 4)
Output Leakage Current, Shutdown
Slew Rate (Notes 5 and 6)
Rise and Fall Time, VOUT = 1VP-P
Small-Signal Bandwidth
Small-Signal Rise and Fall Time
Propagation Delay
Small-Signal Overshoot
Settling Time
Differential Gain (Note 7)
Differential Phase (Note 7)
VS = ±15V
VS = ±15V, Pin 8 Voltage = 0V, TA = 25°C
TA = 25°C
VS = ±5V, RF = 1k, RG = 1k, RL = 150Ω
VS = ±15V, RF = 1k, RG = 1k, RL = 150Ω
VS = ±15V, RF = 1k, RG = 1k, RL = 100Ω
VS = ±15V, RF = 1k, RG = 1k, RL = 100Ω
VS = ±15V, RF = 1k, RG = 1k, RL = 100Ω
0.1%, VOUT = 10V, RF = 1k, RG = 1k, RL = 1k
VS = ±15V, RF = 1k, RG = 1k, RL = 150Ω
VS = ±15V, RF = 1k, RG = 1k, RL = 1k
VS = ±15V, RF = 1k, RG = 1k, RL = 150Ω
VS = ±15V, RF = 1k, RG = 1k, RL = 1k
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: A heat sink may be required depending on the power supply
voltage.
Note 3: The supply current of the LT1227 has a negative temperature
coefficient. For more information, see Typical Performance Characteristics
curves.
●
500
50
50
5
5
72
72
270
240
±13.5
●
Positive Supply Current, Shutdown
MAX
10
10
10
10
80
2
●
Maximum Output Current
Supply Current (Note 3)
60
60
●
VS = ±5V, RL = 150Ω, TA = 25°C
IOUT
IS
TYP
3.5
1100
8.7
140
3.3
3.4
5
50
0.014
0.010
0.010
0.013
15.0
17.5
300
500
300
10
UNITS
µA/V
µA/V
µA/V
µA/V
dB
dB
nA/V
nA/V
µA/V
µA/V
dB
dB
kΩ
kΩ
V
V
V
V
mA
mA
mA
µA
µA
µA
µA
V/µs
ns
MHz
ns
ns
%
ns
%
%
DEG
DEG
Note 4: Ramp Pin 8 voltage down from 15V while measuring IS. When IS
drops to less than 0.5mA, measure Pin 8 current.
Note 5: Slew rate is measured at ±5V on a ±10V output signal while
operating on ±15V supplies with RF = 2k, RG = 220Ω and R L = 400Ω.
Note 6: AC parameters are 100% tested on the ceramic and plastic DIP
package parts (J and N suffix) and are sample tested on every lot of the SO
packaged parts (S suffix).
Note 7: NTSC composite video with an output level of 2V.
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LT1227
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TYPICAL PERFOR A CE CHARACTERISTICS
Voltage Gain and Phase vs
Frequency, Gain = 6dB
135
225
4
3
VS = ±15V
RL = 100Ω
RF = 910Ω
1
0
0.1
RF = 750Ω
100
RF = 1k
80
60
40
RF = 2k
20
0
1
10
FREQUENCY (MHz)
0
100
2
4
6
8 10 12 14
SUPPLY VOLTAGE (±V)
LT1227 • TPC01
135
20
180
GAIN
225
18
17
16
VS = ±15V
RL = 100Ω
RF = 825Ω
15
14
0.1
120
100
RF = 250Ω
RF = 500Ω
80
RF = 750Ω
60
RF = 1k
40
RF = 2k
41
135
40
180
225
37
35
34
0.1
VS = ±15V
RL = 100Ω
RF = 500Ω
2
4
6
8 10 12 14
SUPPLY VOLTAGE (±V)
16
100
18
RF = 500Ω
100
80
RF = 750Ω
60
RF = 1k
40
RF = 2k
0
18
2
4
6
8 10 12 14
SUPPLY VOLTAGE (±V)
18
16
16
14
14
RF = 500Ω
RF = 1k
10
RF = 2k
8
18
LT1227 • TPC06
18
12
16
–3dB Bandwidth vs Supply
Voltage, Gain = 100, RL = 1k
6
4
RF = 500Ω
12
RF = 1k
RF = 2k
10
8
6
4
2
0
0
1
10
FREQUENCY (MHz)
120
20
2
LT1227 • TPC07
4
–3dB BANDWIDTH (MHz)
VOLTAGE GAIN (dB)
90
PHASE SHIFT (DEG)
42
16
PEAKING ≤ 0.5dB
PEAKING ≤ 5dB
LT1227 • TPC05
0
38
6
8 10 12 14
SUPPLY VOLTAGE (±V)
0
0
45
GAIN
4
140
–3dB Bandwidth vs Supply
Voltage, Gain = 100, RL = 100Ω
PHASE
2
LT1227 • TPC03
0
100
44
36
0
–3dB Bandwidth vs Supply
Voltage, Gain = 10, RL = 1k
140
Voltage Gain and Phase vs
Frequency, Gain = 40dB
39
0
160
LT1227 • TPC04
43
40
180
20
1
10
FREQUENCY (MHz)
RF = 1k
60
18
PEAKING ≤ 0.5dB
PEAKING ≤ 5dB
160
–3dB BANDWIDTH (MHz)
VOLTAGE GAIN (dB)
90
21
PHASE SHIFT (DEG)
45
22
19
16
180
0
PHASE
RF = 1.5k
80
–3dB Bandwidth vs Supply
Voltage, Gain = 10, RL = 100Ω
24
RF = 2k
100
LT1227 • TPC02
Voltage Gain and Phase vs
Frequency, Gain = 20dB
23
RF = 750Ω
140
120
20
–3dB BANDWIDTH (MHz)
2
RF = 500Ω
–3dB BANDWIDTH (MHz)
5
180
GAIN
140
120
PEAKING ≤ 0.5dB
PEAKING ≤ 5dB
160
–3dB BANDWIDTH (MHz)
90
7
180
PEAKING ≤ 0.5dB
PEAKING ≤ 5dB
160
–3dB BANDWIDTH (MHz)
VOLTAGE GAIN (dB)
45
PHASE SHIFT (DEG)
PHASE
8
6
180
0
10
9
–3dB Bandwidth vs Supply
Voltage, Gain = 2, RL = 1k
–3dB Bandwidth vs Supply
Voltage, Gain = 2, RL = 100Ω
0
2
4
6
8 10 12 14
SUPPLY VOLTAGE (±V)
16
18
LT1227 • TPC08
0
2
4
6
8 10 12 14
SUPPLY VOLTAGE (±V)
16
18
LT1227 • TPC09
LT1227
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TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Capacitive Load
vs Feedback Resistor
Total Harmonic Distortion
vs Frequency
0.1
10000
VS = ±5V
VS = ±15V
100
10
2
1
FEEDBACK RESISTOR (kΩ)
VO = 7VRMS
3
1k
10k
FREQUENCY (Hz)
OUTPUT SATURATION VOLTAGE (V)
–1.5
–2.0
2.0
1.5
V – = –2V TO –18V
–0.5
70
RL = ∞
±2V ≤ VS ≤ ±18V
–1.0
1.0
0.5
50
25
0
75
TEMPERATURE (°C)
100
V–
–50 –25
125
50
25
75
0
TEMPERATURE (°C)
80
POWER SUPPLY REJECTION (dB)
SPOT NOISE (nV/√Hz OR pA/√Hz)
100
–in
10
en
+in
1
1k
10k
FREQUENCY (Hz)
50
40
30
–50 –25
125
100k
LT1227 • TPC16
25 50 75 100 125 150 175
TEMPERATURE (°C)
0
LT1227 • TPC15
Power Supply Rejection
vs Frequency
Spot Noise Voltage and Current
vs Frequency
100
60
LT1227 • TPC14
LT1227 • TPC13
10
100
Output Impedance vs Frequency
100
VS = ±15V
RL = 100Ω
RF = RG = 1k
60
POSITIVE
NEGATIVE
40
20
VS = ±15V
10
OUTPUT IMPEDANCE (Ω)
–25
100
Output Short-Circuit Current
vs Junction Temperature
0.5
V–
–50
10
FREQUENCY (MHz)
LT1127 • TPC12
OUTPUT SHORT-CIRCUIT CURRENT (mA)
V+
V+
1.0
1
100k
Output Saturation Voltage
vs Temperature
V + = 2V TO 18V
AV = +2
LT1227 • TPC11
Input Common Mode Limit
vs Temperature
–1.0
AV = +1
10
0
100
LT1227 • TPC10
–0.5
AV = +10
AV = –1
15
5
VO = 1VRMS
0.001
10
1
0
0.01
VS = ±15V
RL = 1k
RF = 1k
20
OUTPUT VOLTAGE (VP-P)
CAPACITIVE LOAD (pF)
1000
25
VS = ±15V
RL = 400Ω
RF = RG = 1k
TOTAL HARMONIC DISTORTION (%)
RL = 1k
PEAKING ≤ 5dB
GAIN = 2
COMMON MODE RANGE (V)
Maximum Undistorted Output
vs Frequency
1
RF = RG = 2k
RF = RG = 1k
0.1
0.01
0
10k
100k
1M
10M
FREQUENCY (Hz)
100M
LT1227 • TPC17
0.001
10k
100k
1M
10M
FREQUENCY (Hz)
100M
LT1227 • TPC18
5
LT1227
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TYPICAL PERFOR A CE CHARACTERISTICS
Settling Time to 1mV
vs Output Step
Settling Time to 10mV
vs Output Step
10
VS = ±15V
RF = RG = 1k
8
13
12
4
NONINVERTING
2
INVERTING
0
–2
–4
4
2
NONINVERTING
0
INVERTING
–2
–4
8
–8
5
60
40
SETTLING TIME (ns)
80
–10
100
4
4
0
12
16
8
SETTLING TIME (µs)
1M
10M
FREQUENCY (Hz)
0.10
0.20
VS = ±15V
AV = 2
RL = 1k
RF = 1k
RG = 1k
1M
10M
2ND
3RD
–50
VS = ±15V
AV = 2
RL = 1k
RF = 1k
RG = 1k
0.06
100k
1M
–60
10M
LT1227 • TPC24
Test Circuit for 3rd Order Intercept
VS = ±15V
RL = 100Ω
RF = 680Ω
RG = 75Ω
40
100M
FREQUENCY (Hz)
3rd Order Intercept vs Frequency
3RD ORDER INTERCEPT (dBm)
–40
0.04
LT1227 • TPC23
45
VS = ±15V
VO = 2VP-P
RL = 100Ω
RF = 820Ω
AV = 10dB
–30
100M
(VO)DC = 0.5V
1.0V
2.0V
0.03
0.05
LT1227 • TPC22
–20
0.02
FREQUENCY (Hz)
2nd and 3rd Harmonic Distortion
vs Frequency
18
0.01
0.15
0.30
100k
100M
16
Differential Gain vs Frequency
(VO)DC = 0.5V
1.0V
1.5V
2.0V
0.05
0.25
0.1
100k
6
8 10 12 14
SUPPLY VOLTAGE (±V)
0
DIFFERENTIAL GAIN (%)
1
4
LT1227 • TPC21
0
DIFFERENTIAL PHASE (DEG)
10
2
0
20
Differential Phase vs Frequency
VS = ±15V
AV = 1
RF = 1.5k
175°C
LT1227 • TPC20
Output Impedance in Shutdown
vs Frequency
100
125°C
7
–8
20
25°C
9
6
LT1227 • TPC19
OUTPUT IMPEDANCE (kΩ)
10
–6
0
–55°C
11
–6
–10
DISTORTION (dBc)
SUPPLY CURRENT (mA)
6
OUTPUT STEP (V)
OUTPUT STEP (V)
VS = ±15V
RF = RG = 1k
8
6
Supply Current vs Supply Voltage
14
10
+
50Ω
LT1227
35
PO
–
680Ω
30
25
75Ω
50Ω
MEASURE INTERCEPT AT PO
20
1227 TC
–70
1
10
FREQUENCY (MHz)
100
LT1227 • TPC25
6
15
0
10
20
30
40
FREQUENCY (MHz)
50
60
LT1227 • TPC26
LT1227
W
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SI PLIFIED SCHE ATIC
7
14k
NULL 1
V+
NULL 5
CURRENT
SOURCE
BIAS
8
S/D
+IN 3
2
–IN
6 VOUT
4 V–
1227 SS
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APPLICATI
S I FOR ATIO
The LT1227 is a very fast current feedback amplifier.
Because it is a current feedback amplifier, the bandwidth
is maintained over a wide range of voltage gains. The
amplifier is designed to drive low impedance loads such as
cables with excellent linearity at high frequencies.
Feedback Resistor Selection
The small-signal bandwidth of the LT1227 is set by the
external feedback resistors and the internal junction capacitors. As a result, the bandwidth is a function of the
supply voltage, the value of the feedback resistor, the
closed-loop gain and load resistor. The characteristic
curves of Bandwidth vs Supply Voltage show the effect of
a heavy load (100Ω) and a light load (1k). These curves
use a solid line when the response has less than 0.5dB of
peaking and a dashed line when the response has 0.5dB to
5dB of peaking. The curves stop where the response has
more than 5dB of peaking.
At a gain of two, on ±15V supplies with a 1k feedback
resistor, the bandwidth into a light load is over 140MHz,
but into a heavy load the bandwidth reduces to 120MHz.
The loading has this effect because there is a mild resonance in the output stage that enhances the bandwidth at
light loads but has its Q reduced by the heavy load. This
enhancement is only useful at low gain settlings; at a gain
of ten it does not boost the bandwidth. At unity gain, the
enhancement is so effective the value of the feedback
resistor has very little effect. At very high closed-loop
gains, the bandwidth is limited by the gain bandwidth
product of about 1GHz. The curves show that the bandwidth at a closed-loop gain of 100 is 12MHz, only one tenth
what it is at a gain of two.
7
LT1227
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APPLICATI
S I FOR ATIO
and inverting input bias current will change. The offset
voltage changes about 500µV per volt of supply mismatch. The inverting bias current can change as much as
5.0µA per volt of supply mismatch, though typically the
change is less than 0.5µA per volt.
Small-Signal Rise Time, AV = +2
Slew Rate
VOUT
RF = 1k, RG= 1k, RL = 100Ω
AI01
Capacitance on the Inverting Input
Current feedback amplifiers require resistive feedback
from the output to the inverting input for stable operation.
Take care to minimize the stray capacitance between the
output and the inverting input. Capacitance on the inverting input to ground will cause peaking in the frequency
response (and overshoot in the transient response), but it
does not degrade the stability of the amplifier.
Capacitive Loads
The LT1227 can drive capacitive loads directly when the
proper value of feedback resistor is used. The graph of
Maximum Capacitive Load vs Feedback Resistor should
be used to select the appropriate value. The value shown
is for 5dB peaking when driving a 1k load at a gain of 2. This
is a worst case condition, the amplifier is more stable at
higher gains and driving heavier loads. Alternatively, a
small resistor (10Ω to 20Ω) can be put in series with the
output to isolate the capacitive load from the amplifier
output. This has the advantage that the amplifier bandwidth is only reduced when the capacitive load is present
and the disadvantage that the gain is a function of the load
resistance.
The slew rate of a current feedback amplifier is not
independent of the amplifier gain configuration the way
slew rate is in a traditional op amp. This is because both the
input stage and the output stage have slew rate limitations.
In the inverting mode, and for higher gains in the
noninverting mode, the signal amplitude between the
input pins is small and the overall slew rate is that of the
output stage. For gains less than ten in the noninverting
mode, the overall slew rate is limited by the input stage.
The input stage slew rate of the LT1227 is approximately
125V/µs and is set by internal currents and capacitances.
The output slew rate is set by the value of the feedback
resistors and the internal capacitances. At a gain of ten
with a 1k feedback resistor and ±15V supplies, the output
slew rate is typically 1100V/µs. Larger feedback resistors
will reduce the slew rate as will lower supply voltages,
similar to the way the bandwidth is reduced.
The graph of Maximum Undistorted Output vs Frequency
relates the slew rate limitations to sinusoidal inputs for
various gain configurations.
Large-Signal Transient Response, AV = +10
VOUT
Power Supplies
The LT1227 will operate from single or split supplies from
±2V (4V total) to ±15V (30V total). It is not necessary to
use equal value split supplies, however the offset voltage
8
RF = 910Ω, RG= 100Ω, RL = 400Ω
AI02
LT1227
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UO
APPLICATI
S I FOR ATIO
Shutdown
Large-Signal Transient Response, AV = +2
VOUT
RF = 1k, RG= 1k, RL = 400Ω
AI03
Large-Signal Transient Response, AV = –2
The LT1227 has a high impedance, low supply current
mode which is controlled by Pin 8. In the shutdown mode,
the output looks like a 12pF capacitor and the supply
current drops to approximately the Pin 8 current. The
shutdown pin is referenced to the positive supply through
an internal pullup circuit (see the simplified schematic).
Pulling a current of greater than 50µA from Pin 8 will put
the device into the shutdown mode. An easy way to force
shutdown is to ground Pin 8, using open drain (collector)
logic. Because the pin is referenced to the positive supply,
the logic used should have a breakdown voltage of greater
than the positive supply voltage. No other circuitry is
necessary as an internal JFET limits the Pin 8 current to
about 100µA. When Pin 8 is open, the LT1227 operates
normally.
Differential Input Signal Swing
VOUT
AI04
RF = 1k, RG= 510Ω, RL = 400Ω
AI04
The differential input swing is limited to about ±6V by an
ESD protection device connected between the inputs. In
normal operation, the differential voltage between the
input pins is small, so this clamp has no effect; however,
in the shutdown mode, the differential swing can be the
same as the input swing. The clamp voltage will then set
the maximum allowable input voltage. To allow for some
margin, it is recommended that the input signal be less
than ±5V when the device is shutdown.
Offset Adjust
Settling Time
The characteristic curves show that the LT1227 amplifier
settles to within 10mV of final value in 40ns to 55ns for any
output step up to 10V. The curve of settling to 1mV of final
value shows that there is a slower thermal contribution up
to 20µs. The thermal settling component comes from the
output and the input stage. The output contributes just
under 1mV per volt of output change and the input
contributes 300µV per volt of input change. Fortunately
the input thermal tends to cancel the output thermal. For
this reason the noninverting gain of two configuration
settles faster than the inverting gain of one.
Pins 1 and 5 are provided for offset nulling. A small current
to V + or ground will compensate for DC offsets in the
device. The pins are referenced to the positive supply (see
the simplified schematic) and should be left open if unused. The offset adjust pins act primarily on the inverting
input bias current. A 10k pot connected to Pins 1 and 5
with the wiper connected to V + will null out the bias
current, but will not affect the offset voltage much. Since
the output offset is
VO ≅ AV • VOS + (IIN –) • RF
at higher gains (AV > 5), the VOS term will dominate. To null
out the VOS term, use a 10k pot between Pins 1 and 5 with
a 150k resistor from the wiper to ground for 15V split
supplies, 47k for 5V split supplies.
9
LT1227
UO
TYPICAL APPLICATI
S
MUX Amplifier
MUX Amplifier
The shutdown function can be effectively used to construct a MUX amplifier. A two-channel version is shown,
but more inputs could be added with suitable logic. By
configuring each amplifier as a unity-gain follower, there
is no loading by the feedback network when the amplifier
is off. The open drains of the 74C906 buffers are used to
interface the 5V logic to the shutdown pin. Feedthrough
from the unselected input to the output is –70dB at
10MHz. The differential voltage between MUX inputs VIN1
and VIN2 appears across the inputs of the shutdown
device, this voltage should be less than ±5V to avoid
turning on the clamp diodes discussed previously. If the
inputs are sinusoidal having a zero DC level, this implies
that the amplitude of each input should be less than
5VP-P. The output impedance of the off amplifier remains
high until the output level exceeds approximately 6VP-P at
10MHz, this sets the maximum usable output level. Switching time between inputs is about 4µs without an external
pullup. Adding a 10k pullup resistor from each shutdown
pin to V + will reduce the switching time to 2µs but will
increase the positive supply current in shutdown by 1.5mA.
15V
+
VIN1
LT1227 S/D
VOUT
–
–15V
1.5k
VOUT
=1
VIN
5V
74C906
15V
+
VIN2
LT1227 S/D
–
–15V
1.5k
5V
5V
INPUT
SELECT
74HC04
74C906
1227 TA04
MUX Output
MUX Input Crosstalk vs Frequency
–40
INPUT CROSSTALK (dB)
–50
VOUT
INPUT
SELECT
–60
–70
–80
–90
VIN1 = 1VP-P, VIN2 = 0V
TA03
1
10
FREQUENCY (MHz)
100
LT1227 TA05
10
LT1227
U
PACKAGE DESCRIPTIO
J8 Package
8-Lead CERDIP (Narrow .300 Inch, Hermetic)
(Reference LTC DWG # 05-08-1110)
0.300 BSC
(0.762 BSC)
0.008 – 0.018
(0.203 – 0.457)
CORNER LEADS OPTION
(4 PLCS)
0° – 15°
0.023 – 0.045
(0.584 – 1.143)
HALF LEAD
OPTION
0.045 – 0.068
(1.143 – 1.727)
FULL LEAD
OPTION
NOTE: LEAD DIMENSIONS APPLY TO SOLDER
DIP/PLATE OR TIN PLATE LEADS
0.405
(10.287)
MAX
0.005
(0.127)
MIN
0.015 – 0.060
(0.381 – 1.524)
8
0.014 – 0.026
(0.360 – 0.660)
0.100
(2.54)
BSC
5
0.025
(0.635)
RAD TYP
0.220 – 0.310
(5.588 – 7.874)
1
0.045 – 0.065
(1.143 – 1.651)
6
7
2
3
4
0.200
(5.080)
MAX
0.125
3.175
MIN
J8 1298
OBSOLETE PACKAGE
N8 Package
8-Lead PDIP (Narrow .300 Inch)
(Reference LTC DWG # 05-08-1510)
0.300 – 0.325
(7.620 – 8.255)
0.045 – 0.065
(1.143 – 1.651)
0.065
(1.651)
TYP
0.009 – 0.015
(0.229 – 0.381)
(
0.400*
(10.160)
MAX
0.130 ± 0.005
(3.302 ± 0.127)
8
7
6
5
1
2
3
4
0.255 ± 0.015*
(6.477 ± 0.381)
+0.035
0.325 –0.015
+0.889
8.255
–0.381
)
0.100
(2.54)
BSC
0.125
(3.175) 0.020
MIN
(0.508)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
N8 1098
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
0.016 – 0.050
(0.406 – 1.270)
0.014 – 0.019
(0.355 – 0.483)
TYP
*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
8
7
6
5
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
BSC
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
SO8 1298
1
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
2
3
4
11
LT1227
UO
TYPICAL APPLICATI
S
Single Supply AC-Coupled
Amplifier Noninverting
Single Supply AC-Coupled
Amplifier Inverting
3.58MHz Oscillator
15V
5V
5V
4.7µF
+
+
AV =
10k
22µF
100pF
10k
2.2µF
–
3.579545MHz
+
+
VOUT
75pF
10k
+
LT1227
2N3904
510Ω
≈ 10
RS + 51Ω
BW = 14Hz to 60MHz
+
VIN
1N4148
100k
4.7µF
1k
VOUT
LT1227
10k
68pF
150k
15V
–
–
220µF
510Ω
RS
VIN
AV = 11
BW = 14Hz to 60MHz
+
+
51Ω
51Ω
VOUT
LT1227
220µF
510Ω
51Ω
+
1227 TA09
–15V
1227 TA08
Buffer with DC Nulling Loop
CMOS Logic to Shutdown Interface
1227 TA10
Optional Offset Nulling Circuit
V+
180Ω
RNULL
180Ω
10k
3
0.1µF
3
VIN
5
+
1
LT1227
10k
2
V+
15V
10k
7
3
+
6
LT1227
6
2
VOUT
1
LT1227
2
8
–
5
–
4
4
–15V
V–
–
10k
7
+
6
RNULL = 47k FOR VS = ±5V
RNULL = 150k FOR VS = ±15V
1227 TA12
5V
1.5k
10k
2N3904
100k
0.01µF
1227 TA11
+
100k
LT1097
–
0.01µF
1227 TA07
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1395/LT1396/LT1397 Single/Dual/Quad 400MHz Current Feedback Amplifier
12
Linear Technology Corporation
Miniature Packages: SOT-23, MSOP-8, SSOP-16
1227fb LT/CP 1001 1.5K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
LINEAR TECHNOLOGY CORPORATION 1994
Mouser Electronics
Authorized Distributor
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LT1227CS8#TRPBF LT1227CN8#PBF LT1227CS8#PBF
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