Download LT1993-2

LT1993-2
800MHz Low Distortion, Low
Noise Differential Amplifier/
ADC Driver (AV = 2V/V)
DESCRIPTIO
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FEATURES
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The LT®1993-2 is a low distortion, low noise Differential
Amplifier/ADC driver for use in applications from DC to
800MHz. The LT1993-2 has been designed for ease of
use, with minimal support circuitry required. Exceptionally low input-referred noise and low distortion products
(with either single-ended or differential inputs) make the
LT1993-2 an excellent solution for driving high speed 12bit and 14-bit ADCs. In addition to the normal unfiltered
outputs (+OUT and –OUT), the LT1993-2 has a built-in
175MHz differential low pass filter and an additional pair
of filtered outputs (+OUTFILTERED, –OUTFILTERED) to
reduce external filtering components when driving high
speed ADCs. The output common mode voltage is easily set
via the VOCM pin, eliminating either an output transformer
or AC-coupling capacitors in many applications.
800MHz –3dB Bandwidth
Fixed Gain of 2V/V (6dB)
Low Distortion:
38dBm OIP3, –70dBc HD3 (70MHz, 2VP-P)
51dBm OIP3, –94dBc HD3 (10MHz, 2VP-P)
Low Noise: 12.3dB NF, en = 3.8nV/√Hz (70MHz)
Differential Inputs and Outputs
Additional Filtered Outputs
Adjustable Output Common Mode Voltage
DC- or AC-Coupled Operation
Minimal Support Circuitry Required
Small 0.75mm Tall 16-Lead 3 × 3 QFN Package
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APPLICATIO S
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Differential ADC Driver for:
Imaging
Communications
Differential Driver/Receiver
Single Ended to Differential Conversion
Differential to Single Ended Conversion
Level Shifting
IF Sampling Receivers
SAW Filter Interfacing/Buffering
The LT1993-2 is designed to meet the demanding requirements of communications transceiver applications. It can
be used as a differential ADC driver, a general-purpose
differential gain block, or in any other application requiring differential drive. The LT1993-2 can be used in data
acquisition systems required to function at frequencies
down to DC.
The LT1993-2 operates on a 5V supply and consumes
100mA. It comes in a compact 16-lead 3 × 3 QFN package
and operates over a –40°C to 85°C temperature range.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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TYPICAL APPLICATIO
4-Tone WCDMA Waveform,
LT1993-2 Driving LTC2255 14-Bit
ADC at 92.16Msps
4-Channel WCDMA Receive Channel
–INB
•
•
–INA
0.1µF
MINI-CIRCUITS
TCM4-19
0
32768 POINT FFT
–10 TONE CENTER FREQUENCIES
–20 AT 62.5MHz, 67.5MHz,
72.5MHz, 77.5MHz
–30
0.1µF
12.2Ω
–OUT
–OUTFILTERED
LT1993-2
+OUTFILTERED
+INB
+OUT
+INA
VOCM
ENABLE
2.2V
AIN–
82nH
52.3pF
LTC2255
ADC
AIN+
12.2Ω
LTC2255 125Msps
14-BIT ADC SAMPLING
AT 92.16Msps
19932 TA01a
AMPLITUDE (dBFS)
70MHz
IF IN
1:4
Z-RATIO
–40
–50
–60
–70
–80
–90
–100
–110
–120
0
5
10
15 20 25 30 35
FREQUENCY (MHz)
40
45
19932 TA01b
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19932fa
1
LT1993-2
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W W
W
ABSOLUTE
AXI U RATI GS
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W
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PACKAGE/ORDER I FOR ATIO
(Note 1)
–INB
–INA
+INB
+INA
TOP VIEW
16 15 14 13
VCCC 1
12 VEEC
VOCM 2
11 ENABLE
17
VCCA 3
10 VCCB
VEEA 4
6
7
8
+OUT
–OUTFILTERED
–OUT
9
5
+OUTFILTERED
Total Supply Voltage (VCCA/VCCB/VCCC to
VEEA/VEEB/VEEC) ...................................................5.5V
Input Current (+INA, –INA, +INB, –INB,
VOCM, ENABLE)................................................±10mA
Output Current (Continuous) (Note 6)
+OUT, –OUT (DC) ..........................................±100mA
(AC) ..........................................±100mA
+OUTFILTERED, –OUTFILTERED (DC) .............±15mA
(AC) .............±45mA
Output Short Circuit Duration (Note 2) ............ Indefinite
Operating Temperature Range (Note 3) ... –40°C to 85°C
Specified Temperature Range (Note 4) .... –40°C to 85°C
Storage Temperature Range................... –65°C to 125°C
Junction Temperature ........................................... 125°C
Lead Temperature Range (Soldering 10 sec) ........ 300°C
VEEB
UD PACKAGE
16-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 125°C, θJA = 68°C/W, θJC = 4.2°C/W
EXPOSED PAD IS VEE (PIN 17) MUST BE SOLDERED TO THE PCB
ORDER PART NUMBER
UD PART MARKING*
LT1993CUD-2
LT1993IUD-2
LBJG
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
*The temperature grade is identified by a label on the shipping container.
DC ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCCA = VCCB = VCCC = 5V, VEEA = VEEB = VEEC = 0V, ENABLE = 0.8V, +INA
shorted to +INB (+IN), –INA shorted to –INB (–IN), VOCM = 2.2V, Input common mode voltage = 2.2V, no RLOAD unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input/Output Characteristics (+INA, +INB, –INA, –INB, +OUT, –OUT, +OUTFILTERED, –OUTFILTERED)
GDIFF
Differential (+OUT, –OUT), VIN = ±0.8V Differential
Gain
●
5.8
6.08
6.3
dB
0.25
0.35
0.5
V
V
VSWINGMIN
Single-Ended +OUT, –OUT, +OUTFILTERED,
–OUTFILTERED. VIN = ±2.2V Differential
●
VSWINGMAX
Single-Ended +OUT, –OUT, +OUTFILTERED,
–OUTFILTERED. VIN = ±2.2V Differential
3.6
3.5
3.75
●
VSWINGDIFF Output Voltage Swing
Differential (+OUT, –OUT), VIN = ±2.2V
Differential
6.5
6
7
●
VP-P
VP-P
IOUT
Output Current Drive
(Note 5)
●
±40
±45
mA
VOS
Input Offset Voltage
–6.5
–10
1
●
TCVOS
Input Offset Voltage Drift
TMIN to TMAX
●
IVRMIN
Input Voltage Range, MIN
Single-Ended
●
IVRMAX
Input Voltage Range, MAX
Single-Ended
●
5.1
RINDIFF
Differential Input Resistance
●
170
200
CINDIFF
Differential Input Capacitance
1
pF
CMRR
Common Mode Rejection Ratio
●
45
70
dB
2
Input Common Mode –0.1V to 5.1V
V
V
6.5
10
2.5
µV/°C
–0.1
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mV
mV
V
V
240
Ω
19932fa
LT1993-2
DC ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCCA = VCCB = VCCC = 5V, VEEA = VEEB = VEEC = 0V, ENABLE = 0.8V, +INA
shorted to +INB (+IN), –INA shorted to –INB (–IN), VOCM = 2.2V, Input common mode voltage = 2.2V, no RLOAD unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ROUTDIFF
Output Resistance
0.3
Ω
COUTDIFF
Output Capacitance
0.8
pF
Common Mode Voltage Control (VOCM Pin)
GCM
Differential (+OUT, –OUT), VOCM = 1.1V to 3.6V
Differential (+OUT, –OUT), VOCM = 1.3V to 3.4V
Common Mode Gain
●
VOCMMIN
Output Common Mode Voltage
Adjustment Range, MIN
Measured Single-Ended at +OUT and –OUT
VOCMMAX
Output Common Mode Voltage
Adjustment Range, MAX
Measured Single-Ended at +OUT and –OUT
VOSCM
Output Common Mode Offset Voltage
Measured from VOCM to Average of +OUT and –OUT
IBIASCM
VOCM Input Bias Current
●
RINCM
VOCM Input Resistance
●
CINCM
VOCM Input Capacitance
0.9
0.9
1
●
●
3.6
3.4
●
–30
0.8
1.1
1.1
V/V
V/V
1.1
1.3
V
V
V
V
4
30
mV
5
15
µA
3
MΩ
1
pF
ENABLE Pin
VIL
ENABLE Input Low Voltage
●
VIH
ENABLE Input High Voltage
●
IIL
ENABLE Input Low Current
ENABLE = 0.8V
●
IIH
ENABLE Input High Current
ENABLE = 2V
●
0.8
V
2
V
0.5
µA
1
3
µA
Power Supply
●
4
5
5.5
V
ENABLE = 0.8V
●
88
100
112
mA
Supply Current (Disabled)
ENABLE = 2V
●
250
500
µA
Power Supply Rejection Ratio
4V to 5.5V
●
VS
Operating Range
IS
Supply Current
ISDISABLED
PSRR
55
90
dB
AC ELECTRICAL CHARACTERISTICS
TA = 25°C, VCCA = VCCB = VCCC = 5V, VEEA = VEEB = VEEC = 0V,
ENABLE = 0.8V, +INA shorted to +INB (+IN), –INA shorted to –INB (–IN), VOCM = 2.2V, Input common mode voltage = 2.2V, no RLOAD
unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
500
MAX
UNITS
Input/Output Characteristics
–3dBBW
–3dB Bandwidth
200mVP-P Differential (+OUT, –OUT)
800
MHz
0.1dBBW
Bandwidth for 0.1dB Flatness
200mVP-P Differential (+OUT, –OUT)
50
MHz
0.5dBBW
Bandwidth for 0.5dB Flatness
200mVP-P Differential (+OUT, –OUT)
100
MHz
SR
Slew Rate
3.2VP-P Differential (+OUT, –OUT)
1100
V/µs
ts1%
1% Settling Time
1% Settling for a 1VP-P Differential Step
(+OUT, –OUT)
tON
tOFF
4
ns
Turn-On Time
40
ns
Turn-Off Time
250
ns
Common Mode Voltage Control (VOCM Pin)
–3dBBWCM
Common Mode Small-Signal –3dB
Bandwidth
0.1VP-P at VOCM, Measured Single-Ended at +OUT
and –OUT
300
MHz
SRCM
Common Mode Slew Rate
1.3V to 3.4V Step at VOCM
500
V/µs
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19932fa
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LT1993-2
AC ELECTRICAL CHARACTERISTICS
TA = 25°C, VCCA = VCCB = VCCC = 5V, VEEA = VEEB = VEEC = 0V,
ENABLE = 0.8V, +INA shorted to +INB (+IN), –INA shorted to –INB (–IN), VOCM = 2.2V, Input common mode voltage = 2.2V, no RLOAD
unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Noise/Harmonic Performance Input/output Characteristics
1kHz Signal
Second/Third Harmonic Distortion
Third-Order IMD
OIP31k
Output Third-Order Intercept
en1k
Input Referred Noise Voltage Density
2VP-P Differential (+OUTFILTERED, –OUTFILTERED)
–100
dBc
2VP-P Differential (+OUT, –OUT)
–100
dBc
2VP-P Differential (+OUT, –OUT), RL = 100Ω
–100
dBc
3.2VP-P Differential (+OUTFILTERED, –OUTFILTERED)
–91
dBc
3.2VP-P Differential (+OUT, –OUT)
–91
dBc
3.2VP-P Differential (+OUT, –OUT), RL = 100Ω
–91
dBc
2VP-P Differential Composite (+OUTFILTERED,
–OUTFILTERED), f1 = 0.95kHz, f2 = 1.05kHz
–102
dBc
2VP-P Differential Composite (+OUT, –OUT),
RL = 100Ω, f1 = 0.95kHz, f2 = 1.05kHz
–102
dBc
3.2VP-P Differential Composite (+OUTFILTERED,
–OUTFILTERED), f1 = 0.95kHz, f2 = 1.05kHz
–93
dBc
Differential (+OUTFILTERED, –OUTFILTERED),
f1 = 0.95kHz, f2 = 1.05kHz
54
dBm
3.5
nV/√Hz
1dB Compression Point
RL = 100Ω
22.7
dBm
Second/Third Harmonic Distortion
2VP-P Differential (+OUTFILTERED, –OUTFILTERED)
–94
dBc
2VP-P Differential (+OUT, –OUT)
–94
dBc
2VP-P Differential (+OUT, –OUT), RL = 100Ω
–86
dBc
3.2VP-P Differential (+OUTFILTERED, –OUTFILTERED)
–85
dBc
3.2VP-P Differential (+OUT, –OUT)
–85
dBc
10MHz Signal
Third-Order IMD
3.2VP-P Differential (+OUT, –OUT), RL = 100Ω
–77
dBc
2VP-P Differential Composite (+OUTFILTERED,
–OUTFILTERED), f1 = 9.5MHz, f2 = 10.5MHz
–96
dBc
2VP-P Differential Composite (+OUT, –OUT),
RL = 100Ω, f1 = 9.5MHz, f2 = 10.5MHz
–96
dBc
3.2VP-P Differential Composite (+OUTFILTERED,
–OUTFILTERED), f1 = 9.5MHz, f2 = 10.5MHz
–87
dBc
51
dBm
OIP310M
Output Third-Order Intercept
Differential (+OUTFILTERED, –OUTFILTERED),
f1 = 9.5MHz, f2 = 10.5MHz
NF
Noise Figure
Measured Using DC800A Demo Board
en10M
Input Referred Noise Voltage Density
11.3
dB
3.5
nV/√Hz
1dB Compression Point
RL = 100Ω
22.6
dBm
Second/Third Harmonic Distortion
2VP-P Differential (+OUTFILTERED, –OUTFILTERED)
–77
dBc
2VP-P Differential (+OUT, –OUT)
–77
dBc
2VP-P Differential (+OUT, –OUT), RL = 100Ω
–74
dBc
3.2VP-P Differential (+OUTFILTERED, –OUTFILTERED)
–68
dBc
3.2VP-P Differential (+OUT, –OUT)
–65
50MHz Signal
4
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dBc
19932fa
LT1993-2
AC ELECTRICAL CHARACTERISTICS
TA = 25°C, VCCA = VCCB = VCCC = 5V, VEEA = VEEB = VEEC = 0V,
ENABLE = 0.8V, +INA shorted to +INB (+IN), –INA shorted to –INB (–IN), VOCM = 2.2V, Input common mode voltage = 2.2V, no RLOAD
unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
Third-Order IMD
MIN
TYP
MAX
UNITS
3.2VP-P Differential (+OUT, –OUT), RL = 100Ω
–65
dBc
2VP-P Differential Composite (+OUTFILTERED,
–OUTFILTERED), f1 = 49.5MHz, f2 = 50.5MHz
–84
dBc
2VP-P Differential Composite (+OUT, –OUT),
RL = 100Ω, f1 = 49.5MHz, f2 = 50.5MHz
–88
dBc
3.2VP-P Differential Composite (+OUTFILTERED,
–OUTFILTERED), f1 = 49.5MHz, f2 = 50.5MHz
–75
dBc
45
dBm
OIP350M
Output Third-Order Intercept
Differential (+OUTFILTERED, –OUTFILTERED),
f1 = 49.5MHz, f2 = 50.5MHz
NF
Noise Figure
Measured Using DC800A Demo Board
en50M
Input Referred Noise Voltage Density
11.8
dB
3.65
nV/√Hz
1dB Compression Point
RL = 100Ω
19.7
dBm
Second/Third Harmonic Distortion
2VP-P Differential (+OUTFILTERED, –OUTFILTERED)
–70
dBc
70MHz Signal
Third-Order IMD
2VP-P Differential (+OUT, –OUT)
–61
dBc
2VP-P Differential (+OUT, –OUT), RL = 100Ω
–61
dBc
2VP-P Differential Composite (+OUTFILTERED,
–OUTFILTERED), f1 = 69.5MHz, f2 = 70.5MHz
–70
dBc
2VP-P Differential Composite (+OUT, –OUT),
RL = 100Ω, f1 = 69.5MHz, f2 = 70.5MHz
–72
dBc
38
dBm
OIP370M
Output Third-Order Intercept
Differential (+OUTFILTERED, –OUTFILTERED),
f1 = 69.5MHz, f2 = 70.5MHz
NF
Noise Figure
Measured Using DC800A Demo Board
12.3
dB
en70M
Input Referred Noise Voltage Density
3.8
nV/√Hz
1dB Compression Point
RL = 100Ω
18.5
dBm
Second/Third Harmonic Distortion
2VP-P Differential (+OUTFILTERED, –OUTFILTERED)
–56
dBc
2VP-P Differential (+OUT, –OUT)
–54
dBc
100MHz Signal
Third-Order IMD
2VP-P Differential (+OUT, –OUT), RL = 100Ω
–51
dBc
2VP-P Differential Composite (+OUTFILTERED,
–OUTFILTERED), f1 = 99.5MHz, f2 = 100.5MHz
–58
dBc
2VP-P Differential Composite (+OUT, –OUT),
RL = 100Ω, f1 = 99.5MHz, f2 = 100.5MHz
–59
dBc
32
dBm
OIP3100M
Output Third-Order Intercept
Differential (+OUTFILTERED, –OUTFILTERED),
f1 = 99.5MHz, f2 = 100.5MHz
NF
Noise Figure
Measured Using DC800A Demo Board
en100M
Input Referred Noise Voltage Density
1dB Compression Point
RL = 100Ω
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: As long as output current and junction temperature are kept below
the Absolute Maximum Ratings, no damage to the part will occur.
Note 3: The LT1993C-2 is guaranteed functional over the operating
temperature range of –40°C to 85°C.
Note 4: The LT1993C-2 is guaranteed to meet specified performance from
12.8
dB
4.1
nV/√Hz
17.8
dBm
0°C to 70°C. It is designed, characterized and expected to meet specified
performance from –40°C and 85°C but is not tested or QA sampled
at these temperatures. The LT1993I-2 is guaranteed to meet specified
performance from –40°C to 85°C.
Note 5: This parameter is pulse tested.
Note 6: This parameter is guaranteed to meet specified performance
through design and characterization. It has not been tested.
19932fa
www.BDTIC.com/Linear
5
LT1993-2
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Frequency Response
RLOAD = 400Ω
Frequency Response vs CLOAD,
RLOAD = 400Ω
12
21
9
Frequency Response
RLOAD = 100Ω
12
VIN = 100mVP-P
UNFILTERED OUTPUTS
18
9
UNFILTERED OUTPUTS
UNFILTERED OUTPUTS
0
–3 V = 100mV
IN
P-P
UNFILTERED: R
= 400Ω
–6 FILTERED: R LOAD
LOAD =
350Ω (EXTERNAL) +
–9 50Ω (INTERNAL, FILTERED
OUTPUTS)
–12
10
1
100
1000
FREQUENCY (MHz)
15
6
12
3
GAIN (dB)
FILTERED OUTPUTS
3
GAIN (dB)
9
6
3
0pF
2pF
5pF
10pF
0
–3
10000
10
1
100
1000
FREQUENCY (MHz)
19932 G01
–3 V = 100mV
IN
P-P
UNFILTERED: R
= 100Ω
–6 FILTERED: R LOAD
LOAD =
50Ω (EXTERNAL) +
–9 50Ω (INTERNAL, FILTERED
OUTPUTS)
–12
10
1
100
1000
FREQUENCY (MHz)
Third Order Intermodulation
Distortion vs Frequency
Differential Input, RLOAD = 100Ω
–10
–10
–10
–30
–30
–30
–50
–60
FILTERED OUTPUTS
–70
2 TONES, 2VP-P COMPOSITE
–20 1MHz TONE SPACING
2 TONES, 2VP-P COMPOSITE
–20 1MHz TONE SPACING
THIRD ORDER IMD (dBc)
2 TONES, 2VP-P COMPOSITE
–20 1MHz TONE SPACING
–80
UNFILTERED OUTPUTS
–40
–50
–60
FILTERED OUTPUTS
–70
–80
UNFILTERED OUTPUTS
–40
–50
–60
–100
–100
–100
–110
–110
20
40
60
80 100
FREQUENCY (MHz)
120
140
–110
0
20
40
60
80 100
FREQUENCY (MHz)
19932 G04
60
FILTERED OUTPUTS
35
45
UNFILTERED OUTPUTS
40
35
FILTERED OUTPUTS
45
UNFILTERED OUTPUTS
40
30
25
25
25
40
60
80 100
FREQUENCY (MHz)
120
140
19932 G07
20
20
0
20
40
60
80 100
FREQUENCY (MHz)
120
140
FILTERED OUTPUTS
35
30
20
140
50
30
0
120
2 TONES, 2VP-P COMPOSITE
1MHz TONE SPACING
55
OUTPUT IP3 (dBm)
OUTPUT IP3 (dBm)
OUTPUT IP3 (dBm)
40
20
6
60
50
UNFILTERED OUTPUTS
40
60
80 100
FREQUENCY (MHz)
Output Third Order Intercept vs
Frequency, Differential Input,
RLOAD = 100Ω
2 TONES, 2VP-P COMPOSITE
1MHz TONE SPACING
55
50
45
20
0
19932 G06
Output Third Order Intercept vs
Frequency, Differential Input,
RLOAD = 400Ω
2 TONES, 2VP-P COMPOSITE
1MHz TONE SPACING
55
140
19932 G05
Output Third Order Intercept vs
Frequency, Differential Input,
No RLOAD
60
120
UNFILTERED OUTPUTS
–80
–90
0
FILTERED OUTPUTS
–70
–90
–90
10000
19932 G02
Third Order Intermodulation
Distortion vs Frequency
Differential Input, RLOAD = 400Ω
–40
FILTERED OUTPUTS
0
19932 G03
Third Order Intermodulation
Distortion vs Frequency
Differential Input, No RLOAD
THIRD ORDER IMD (dBc)
10000
THIRD ORDER IMD (dBc)
GAIN (dB)
6
0
19932 G08
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20
40
60
80 100
FREQUENCY (MHz)
120
140
19932 G09
19932fa
LT1993-2
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Distortion (Filtered) vs Frequency
Differential Input, RLOAD = 400Ω
Distortion (Filtered) vs Frequency
Differential Input, No RLOAD
–10
–10
–10
–30
–30
–30
–40
–40
–40
DISTORTION (dBc)
DISTORTION (dBc)
HD3
–50
–60
HD2
–70
–80
FILTERED OUTPUTS
–20 VOUT = 2VP-P
HD3
–50
–60
HD2
–70
–80
–70
–80
–90
–100
–100
–100
–110
–110
–110
10
100
FREQUENCY (MHz)
1
1000
1000
–10
Distortion (Unfiltered) vs
Frequency, Differential Input,
RLOAD = 100Ω
–10
–10
UNFILTERED OUTPUTS
–20 VOUT = 2VP-P
UNFILTERED OUTPUTS
–20 VOUT = 2VP-P
–30
HD3
DISTORTION (dBc)
HD2
–60
–70
–80
–30
HD3
–40
DISTORTION (dBc)
UNFILTERED OUTPUTS
–20 VOUT = 2VP-P
–50
–50
HD2
–60
–70
–80
–50
–70
–80
–90
–100
–100
–100
–110
1000
–110
10
100
FREQUENCY (MHz)
1
19932 G13
–50
–50
–55
–55
HD3 UNFILTERED OUTPUTS
–70
–75
–80
HD2 FILTERED OUTPUTS
–85
HD3 FILTERED OUTPUTS
–90
–50
1
3
5
7
9
OUTPUT AMPLITUDE (dBm)
11
19932 G16
–55
HD3 UNFILTERED OUTPUTS
–60
–60
–65 HD2 UNFILTERED OUTPUTS
–65
–70
–75
–80
–85
HD2 FILTERED OUTPUTS
–100
HD3 UNFILTERED OUTPUTS
HD3 FILTERED OUTPUTS
–70
–75
–80
HD2 UNFILTERED OUTPUTS
–85
–90
HD3 FILTERED OUTPUTS
–95
–1
Distortion vs Output Amplitude
70MHz Differential Input,
RLOAD = 100Ω
–90
–95
–100
DISTORTION (dBc)
HD2 UNFILTERED OUTPUTS
1000
19932 G15
Distortion vs Output Amplitude
70MHz Differential Input,
RLOAD = 400Ω
–65
10
100
FREQUENCY (MHz)
1
19932 G14
Distortion vs Output Amplitude
70MHz Differential Input,
No RLOAD
–60
1000
DISTORTION (dBc)
10
100
FREQUENCY (MHz)
HD2
–60
–90
–110
HD3
–40
–90
1
1000
19932 G12
Distortion (Unfiltered) vs
Frequency, Differential Input,
RLOAD = 400Ω
Distortion (Unfiltered) vs
Frequency, Differential Input,
No RLOAD
–40
10
100
FREQUENCY (MHz)
1
19932 G11
19932 G10
–30
HD2
–60
–90
10
100
FREQUENCY (MHz)
HD3
–50
–90
1
DISTORTION (dBc)
DISTORTION (dBc)
FILTERED OUTPUTS
–20 VOUT = 2VP-P
FILTERED OUTPUTS
–20 VOUT = 2VP-P
DISTORTION (dBc)
Distortion (Filtered) vs Frequency
Differential Input, RLOAD = 100Ω
–1
1
3
5
7
9
OUTPUT AMPLITUDE (dBm)
11
HD2 FILTERED OUTPUTS
–95
–100
–1
19932 G17
www.BDTIC.com/Linear
1
3
5
7
9
OUTPUT AMPLITUDE (dBm)
11
19932 G18
19932fa
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LT1993-2
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TYPICAL PERFOR A CE CHARACTERISTICS
Distortion (Filtered) vs Frequency
Single-Ended Input, No RLOAD
Distortion (Filtered) vs Frequency
Single-Ended Input, RLOAD = 400Ω
–10
–10
–30
–30
–40
–40
HD3
–50
HD2
–70
–80
FILTERED OUTPUTS
–20 VOUT = 2VP-P
–30
HD3
–50
HD2
–60
–70
–80
–50
–70
–80
–90
–100
–100
–100
–110
–110
–110
10
100
FREQUENCY (MHz)
1
1000
1000
–10
–10
UNFILTERED OUTPUTS
–20 VOUT = 2VP-P
UNFILTERED OUTPUTS
–20 VOUT = 2VP-P
–30
DISTORTION (dBc)
HD3
HD2
–70
–80
–30
HD3
–40
DISTORTION (dBc)
–30
DISTORTION (dBc)
Distortion (Unfiltered) vs
Frequency, Single-Ended Input,
RLOAD = 100Ω
–10
UNFILTERED OUTPUTS
–20 VOUT = 2VP-P
–60
–50
HD2
–60
–70
–80
–50
–70
–80
–90
–90
–100
–100
–110
1000
–110
10
100
FREQUENCY (MHz)
1
19932 G22
–50
–50
–55
–55
HD3 UNFILTERED OUTPUTS
DISTORTION (dBc)
–70
–75
–80
–85
HD2 UNFILTERED OUTPUTS
–90
–95
–100
–1
1
3
5
7
9
OUTPUT AMPLITUDE (dBm)
–50
11
–55
HD3 UNFILTERED OUTPUTS
–60
–65 HD3 FILTERED OUTPUTS
–65
–70
–75
–80
–85
HD2 UNFILTERED OUTPUTS
–100
HD3 UNFILTERED OUTPUTS
HD3 FILTERED OUTPUTS
–70
–75
–80
HD2 UNFILTERED OUTPUTS
–85
HD2 FILTERED OUTPUTS
–90
HD2 FILTERED OUTPUTS
–95
19932 G25
8
19932 G24
–60
–90
HD2 FILTERED OUTPUTS
1000
Distortion vs Output Amplitude
70MHz Single-Ended Input,
RLOAD = 100Ω
Distortion vs Output Amplitude
70MHz Single-Ended Input,
RLOAD = 400Ω
–65 HD3 FILTERED OUTPUTS
10
100
FREQUENCY (MHz)
1
19932 G23
Distortion vs Output Amplitude
70MHz Single-Ended Input,
No RLOAD
–60
1000
DISTORTION (dBc)
10
100
FREQUENCY (MHz)
HD2
–60
–90
–110
HD3
–40
–100
1
1000
19932 G21
Distortion (Unfiltered) vs
Frequency, Single-Ended Input,
RLOAD = 400Ω
Distortion (Unfiltered) vs
Frequency, Single-Ended Input,
No RLOAD
–50
10
100
FREQUENCY (MHz)
1
19932 G20
19932 G19
–40
HD2
–60
–90
10
100
FREQUENCY (MHz)
HD3
–40
–90
1
DISTORTION (dBc)
DISTORTION (dBc)
DISTORTION (dBc)
DISTORTION (dBc)
–10
FILTERED OUTPUTS
–20 VOUT = 2VP-P
FILTERED OUTPUTS
–20 VOUT = 2VP-P
–60
Distortion (Filtered) vs Frequency
Single-Ended Input, RLOAD = 100Ω
–95
–1
1
3
5
7
9
OUTPUT AMPLITUDE (dBm)
11
–100
–1
19932 G26
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1
3
5
7
9
OUTPUT AMPLITUDE (dBm)
11
19932 G27
19932fa
LT1993-2
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TYPICAL PERFOR A CE CHARACTERISTICS
Output 1dB Compression
vs Frequency
25
20
RLOAD = 100Ω
20
15
10
5
15
10
0
5
–5
–10
0
10
100
FREQUENCY (MHz)
VCC = 5V
MEASURED USING DC800A DEMO BOARD
10
1000
100
FREQUENCY (MHz)
19932 G28
INPUT IMPEDANCE (MAGNITUDE Ω, PHASE°)
–50
ISOLATION (dB)
–60
–70
–80
–90
–100
–110
10
100
1000
FREQUENCY (MHz)
2
10
100
IMPEDANCE MAGNITUDE
150
100
50
0
10
1
IMPEDANCE PHASE
–100
0.1
1
10
100
FREQUENCY (MHz)
1
1000
–25
–30
–35
–40
–45
–50
PSRR, CMRR vs Frequency
100
MEASURED USING DC800A DEMO BOARD
–5
90
–10
80
–15
70
–20
–25
–30
–35
19932 G34
UNFILTERED OUTPUTS
CMRR
60
50
40
30
–40
20
–45
10
PSRR
0
–50
1000
1000
19932 G33
PSRR, CMRR (dB)
–20
10
100
FREQUENCY (MHz)
19932 G32
OUTPUT REFLECTION COEFFICIENT (S22)
–15
UNFILTERED OUTPUTS
–50
0
–10
1000
19932 G30
Output Reflection Coefficient vs
Frequency
MEASURED USING DC800A DEMO BOARD
100
FREQUENCY (MHz)
Differential Output Impedance vs
Frequency
200
10000
–5
100
FREQUENCY (MHz)
4
250
Input Reflection Coefficient vs
Frequency
10
6
0
300
19932 G31
0
8
Differential Input Impedance vs
Frequency
UNFILTERED OUTPUTS
1
10
19932 G29
Isolation vs Frequency
–40
12
1000
OUTPUT IMPEDANCE (Ω)
1
INPUT REFLECTION COEFFICIENT (S11)
INPUT REFERRED NOISE VOLTAGE (nV/√Hz)
25
UNFILTERED OUTPUTS
RLOAD = 400Ω
NOISE FIGURE (dB)
OUTPUT 1dB COMPRESSION (dBm)
30
Input Referred Noise Voltage vs
Frequency
Noise Figure vs Frequency
10
100
FREQUENCY (MHz)
1000
1
19932 G35
www.BDTIC.com/Linear
10
100
FREQUENCY (MHz)
1000
19932 G36
19932fa
9
LT1993-2
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Small-Signal Transient Response
Large-Signal Transient Response
3.0
RLOAD = 100Ω PER OUTPUT
Overdrive Recovery Time
4.0
RLOAD = 100Ω PER OUTPUT
2.8
3.5
2.24
2.6
3.0
2.22
2.20
2.18
2.16
2.14
OUTPUT VOLTAGE (V)
2.26
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
2.28
2.4
2.2
2.0
1.8
1.6
2.12
2.5
5
10 15 20 25 30 35 40 45 50
TIME (ns)
1.5
1.0
0
5
10 15 20 25 30 35 40 45 50
TIME (ns)
19932 G37
0
19932 G39
Turn-On Time
Turn-Off Time
4
4
+OUT
+OUT
3
–66
3
2
–OUT
HD3
–72
–OUT
1
0
RLOAD = 100Ω PER OUTPUT
4
2
–74
–76
1.2
1
0
4
ENABLE
2
ENABLE
HD2
0
0
–2
1.4 1.6 1.8 2.0 2.2 2.4 2.6
OUTPUT COMMON MODE VOLTAGE (V)
19932 G40
10
VOLTAGE (V)
VOLTAGE (V)
DISTORTION (dBc)
2
–70
25 50 75 100 125 150 175 200 225 250
TIME (ns)
19932 G38
FILTERED OUTPUTS, NO RLOAD
VOUT = 70MHz 2VP-P
–68
–OUT
0.5
0
Distortion vs Output Common
Mode Voltage LT1993-2 Driving
LTC2249 14-Bit ADC
–64
RLOAD = 100Ω
PER OUTPUT
2.0
1.4
0
+OUT
0
125
250
375
TIME (ns)
500
625
RLOAD = 100Ω PER OUTPUT
–2
0
19932 G41
www.BDTIC.com/Linear
125
250
375
TIME (ns)
500
625
19932 G42
19932fa
LT1993-2
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TYPICAL PERFOR A CE CHARACTERISTICS
50MHz 8192 Point FFT, LT1993-2
Driving LTC2249 14-Bit ADC
0
8192 POINT FFT
–10 fIN = 50MHz, –1dBFS
–20 FILTERED OUTPUTS
–10
–30
–30
–30
–50
–60
–70
–80
0
–40
–50
–60
–70
–80
–40
–50
–60
–70
–80
–90
–90
–90
–100
–100
–100
–110
–110
–110
–120
–120
5
10
15 20 25 30
FREQUENCY (MHz)
35
40
0
5
10
15 20 25 30
FREQUENCY (MHz)
–120
35
19932 G46
–40
–50
–60
–70
–80
–30
–40
–50
–60
–70
–80
–60
–70
–80
–90
–100
–100
–110
–110
–110
–120
–120
15 20 25 30
FREQUENCY (MHz)
35
40
0
5
10
15 20 25 30 35
FREQUENCY (MHz)
40
–50
–100
10
35
–40
–90
5
15 20 25 30
FREQUENCY (MHz)
0
32768 POINT FFT
–10 TONE CENTER FREQUENCIES
–20 AT 62.5MHz, 67.5MHz,
72.5MHz, 77.5MHz
–30
–90
0
10
19932 G48
0
32768 POINT FFT
–10 TONE CENTER FREQUENCIES
–20 AT 67.5MHz, 72.5MHz
AMPLITUDE (dBFS)
–30
5
4-Tone WCDMA Waveform,
LT1993-2 Driving LTC2255 14-Bit
ADC at 92.16Msps
2-Tone WCDMA Waveform,
LT1993-2 Driving LTC2255 14-Bit
ADC at 92.16Msps
32768 POINT FFT
TONE 1 AT 69.5MHz, –7dBFS
TONE 2 AT 70.5MHz, –7dBFS
FILTERED OUTPUTS
–20
0
AMPLITUDE (dBFS)
0
40
19932 G47
70MHz 2-Tone 32768 Point FFT,
LT1993-2 Driving LTC2249
14-Bit ADC
–10
8192 POINT FFT
fIN = 70MHz, –1dBFS
FILTERED OUTPUTS
–20
AMPLITUDE (dBFS)
–40
0
AMPLITUDE (dBFS)
70MHz 8192 Point FFT, LT1993-2
Driving LTC2249 14-Bit ADC
0
8192 POINT FFT
–10 fIN = 30MHz, –1dBFS
–20 FILTERED OUTPUTS
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
30MHz 8192 Point FFT, LT1993-2
Driving LTC2249 14-Bit ADC
40
45
–120
0
19932 G50
5
10
15 20 25 30 35
FREQUENCY (MHz)
40
45
19932 G51
19932 G49
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19932fa
11
LT1993-2
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PI FU CTIO S
VOCM (Pin 2): This pin sets the output common mode
voltage. Without additional biasing, both inputs bias to
this voltage as well. This input is high impedance.
VCCA, VCCB, VCCC (Pins 3, 10, 1): Positive Power Supply
(Normally Tied to 5V). All three pins must be tied to the
same voltage. Bypass each pin with 1000pF and 0.1µF
capacitors as close to the package as possible. Split
supplies are possible as long as the voltage between VCC
and VEE is 5V.
VEEA, VEEB, VEEC (Pins 4, 9, 12): Negative Power Supply
(Normally Tied to Ground). All three pins must be tied to
the same voltage. Split supplies are possible as long as
the voltage between VCC and VEE is 5V. If these pins are
not tied to ground, bypass each pin with 1000pF and 0.1µF
capacitors as close to the package as possible.
+OUT, –OUT (Pins 5, 8): Outputs (Unfiltered). These
pins are high bandwidth, low-impedance outputs. The DC
output voltage at these pins is set to the voltage applied
at VOCM.
12
+OUTFILTERED, –OUTFILTERED (Pins 6, 7): Filtered
Outputs. These pins add a series 25Ω resistor from the
unfiltered outputs and three 12pF capacitors. Each output
has 12pF to VEE, plus an additional 12pF between each pin
(See the Block Diagram). This filter has a –3dB bandwidth
of 175MHz.
ENABLE (Pin 11): This pin is a TTL logic input referenced
to the VEEC pin. If low, the LT1993-2 is enabled and draws
typically 100mA of supply current. If high, the LT1993-2
is disabled and draws typically 250µA.
+INA, +INB (Pins 15, 16): Positive Inputs. These pins are
normally tied together. These inputs may be DC- or ACcoupled. If the inputs are AC-coupled, they will self-bias
to the voltage applied to the VOCM pin.
–INA, –INB (Pins 14, 13): Negative Inputs. These pins are
normally tied together. These inputs may be DC- or ACcoupled. If the inputs are AC-coupled, they will self-bias
to the voltage applied to the VOCM pin.
Exposed Pad (Pin 17): Tie the pad to VEEC (Pin 12). If split
supplies are used, DO NOT tie the pad to ground.
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19932fa
LT1993-2
W
BLOCK DIAGRA
200Ω
–INA
200Ω
12pF
–
14
–INB
VEEA
VCCA
+OUT
5
A
200Ω
+OUTFILTERED
+
13
6
25Ω
VEEA
VCCC
200Ω
VOCM
+
2
C
12pF
–
VEEC
200Ω
25Ω
+INA
7
+
16
+INB
–OUTFILTERED
VCCB
200Ω
–OUT
8
B
200Ω
–
15
12pF
VEEB
VEEB
200Ω
BIAS
3
10
VCCA
1
VCCB
11
VCCC
4
ENABLE
9
VEEA
19932 BD
12
VEEB
VEEC
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19932fa
13
LT1993-2
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APPLICATIO S I FOR ATIO
Circuit Description
Input Impedance and Matching Networks
The LT1993-2 is a low-noise, low-distortion differential
amplifier/ADC driver with:
Because of the internal feedback network, calculation of
the LT1993-2’s input impedance is not straightforward
from examination of the block diagram. Furthermore, the
input impedance when driven differentially is different than
when driven single-ended. When driven differentially, the
LT1993-2’s input impedance is 200Ω (differential); when
driven single-ended, the input impedance is 133Ω.
• DC to 800MHz –3dB bandwidth
• Fixed gain of 2V/V (6dB) independent of RLOAD
• 200Ω differential input impedance
• Low output impedance
• Built-in, user adjustable output filtering
• Requires minimal support circuitry
Referring to the block diagram, the LT1993-2 uses a closedloop topology which incorporates 3 internal amplifiers.
Two of the amplifiers (A and B) are identical and drive
the differential outputs. The third amplifier (C) is used
to set the output common mode voltage. Gain and input
impedance are set by the 200Ω resistors in the internal
feedback network. Output impedance is low, determined
by the inherent output impedance of amplifiers A and B,
and further reduced by internal feedback.
The LT1993-2 also includes built-in single-pole output
filtering. The user has the choice of using the unfiltered
outputs, the filtered outputs (175MHz –3dB lowpass), or
modifying the filtered outputs to alter frequency response
by adding additional components. Many lowpass and
bandpass filters are easily implemented with just one or
two additional components.
The LT1993-2 has been designed to minimize the need
for external support components such as transformers or
AC-coupling capacitors. As an ADC driver, the LT1993-2
requires no external components except for power-supply
bypass capacitors. This allows DC-coupled operation for
applications that have frequency ranges including DC.
At the outputs, the common mode voltage is set via the
VOCM pin, allowing the LT1993-2 to drive ADCs directly. No
output AC-coupling capacitors or transformers are needed.
At the inputs, signals can be differential or single-ended
with virtually no difference in performance. Furthermore,
DC levels at the inputs can be set independently of the
output common mode voltage. These input characteristics
often eliminate the need for an input transformer and/or
AC-coupling capacitors.
14
For single-ended 50Ω applications, an 80.6Ω shunt
matching resistor to ground will result in the proper input
termination (Figure 1). For differential inputs there are
several termination options. If the input source is 50Ω
differential, then input matching can be accomplished by
either a 67Ω shunt resistor across the inputs (Figure 3),
or a 33Ω shunt resistor on each of the inputs to ground
(Figure 2). If additional AC gain is desired, a 1:4 impedance
ratio transformer (like the Mini-Circuits TCM4-19) can also
be used to better match impedances and to provide an additional 6dB of gain (Figure 4). With a 1:4 impedance ratio
transformer, ideal matching impedance at the transformer
output is 200Ω, so no termination resistors are required
to match the LT1993-2’s 200Ω input impedance.
13
14
–INB
–INA
–OUT
8
0.1µF
LT1993-2
15
IF IN
16
80.6Ω
+INB
+OUT
+INA
5
ZIN = 50Ω
SINGLE-ENDED
19932 F01
Figure 1. Input Termination for Single-Ended 50Ω
Input Impedance
13
IF IN–
ZIN = 50Ω
DIFFERENTIAL
14
–INB
–INA
–OUT
8
33Ω
LT1993-2
15
IF IN+
16
33Ω
+INB
+INA
+OUT
5
19932 F02
Figure 2. Input Termination for Differential 50Ω Input Impedance
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19932fa
LT1993-2
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APPLICATIO S I FOR ATIO
13
IF IN–
–INB
14
ZIN = 50Ω
DIFFERENTIAL
67Ω
8
5
Wideband Applications
(Using the +OUT and –OUT Pins)
LT1993-2
15
IF IN+
–OUT
–INA
high impedance inputs of these differential ADCs. If the
filtered outputs are used, then cutoff frequency and the
type of filter can be tailored for the specific application if
needed.
+INB
16
+OUT
+INA
19932 F02
Figure 3. Alternate Input Termination for Differential
50Ω Input Impedance
13
14
–INB
–INA
0.1µF
ZIN = 50Ω
DIFFERENTIAL
8
LT1993-2
15
16
1:4 TRANSFORMER
(MINI-CIRCUITS TCM4-19)
–OUT
+INB
+INA
+OUT
5
19932 F04
Figure 4. Input Termination for Differential 50Ω Input Impedance
with 6dB Additional Gain
In applications where the full bandwidth of the LT1993-2
is desired, the unfiltered output pins (+OUT and –OUT)
should be used. They have a low output impedance;
therefore, gain is unaffected by output load. Capacitance
in excess of 5pF placed directly on the unfiltered outputs
results in additional peaking and reduced performance.
When driving an ADC directly, a small series resistance
is recommended between the LT1993-2’s outputs and
the ADC inputs (Figure 5). This resistance helps eliminate
any resonances associated with bond wire inductances of
either the ADC inputs or the LT1993-2’s outputs. A value
between 10Ω and 25Ω gives excellent results.
Single-Ended to Differential Operation
–OUT
The LT1993-2’s performance with single-ended inputs is
comparable to its performance with differential inputs.
This excellent single-ended performance is largely due
to the internal topology of the LT1993-2. Referring to
the block diagram, if the +INA and +INB pins are driven
with a single-ended signal (while –INA and –INB are tied
to AC ground), then the +OUT and –OUT pins are driven
differentially without any voltage swing needed from
amplifier C. Single-ended to differential conversion using
more conventional topologies suffers from performance
limitations due to the common mode amplifier.
Driving ADCs
The LT1993-2 has been specifically designed to interface
directly with high speed Analog to Digital Converters
(ADCs). In general, these ADCs have differential inputs,
with an input impedance of 1k or higher. In addition, there
is generally some form of lowpass or bandpass filtering just
prior to the ADC to limit input noise at the ADC, thereby
improving system signal to noise ratio. Both the unfiltered
and filtered outputs of the LT1993-2 can easily drive the
8
10Ω TO 25Ω
LT1993-2
ADC
10Ω TO 25Ω
+OUT
5
19932 F05
Figure 5. Adding Small Series R at LT1993-2 Output
Filtered Applications
(Using the +OUTFILTERED and –OUTFILTERED Pins)
Filtering at the output of the LT1993-2 is often desired to
provide either anti-aliasing or improved signal to noise
ratio. To simplify this filtering, the LT1993-2 includes an
additional pair of differential outputs (+OUTFILTERED
and –OUTFILTERED) which incorporate an internal lowpass filter network with a –3dB bandwidth of 175MHz
(Figure 6). These pins each have an output impedance
of 25Ω. Internal capacitances are 12pF to VEE on each
filtered output, plus an additional 12pF capacitor connected differentially between the two filtered outputs. This
resistor/capacitor combination creates filtered outputs
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19932fa
15
LT1993-2
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APPLICATIO S I FOR ATIO
that look like a series 25Ω resistor with a 36pF capacitor
shunting each filtered output to AC ground, giving a –3dB
bandwidth of 175MHz.
LT1993-2
VEE
25Ω
8 –OUT
12pF
7 –OUTFILTERED
FILTERED OUTPUT
(175MHz)
12pF
25Ω
6 +OUTFILTERED
it will appear at each filtered output as a single-ended
capacitance of twice the value. To halve the filter bandwidth, for example, two 36pF capacitors could be added
(one from each filtered output to ground). Alternatively
one 18pF capacitor could be added between the filtered
outputs, again halving the filter bandwidth. Combinations
of capacitors could be used as well; a three capacitor
solution of 12pF from each filtered output to ground plus
a 12pF capacitor between the filtered outputs would also
halve the filter bandwidth (Figure 8).
12pF
VEE
LT1993-2
5 +OUT
VEE
8 –OUT
19932 F06
25Ω
Figure 6. LT1993-2 Internal Filter Topology –3dB BW ≈175MHz
The filter cutoff frequency is easily modified with just a
few external components. To increase the cutoff frequency,
simply add 2 equal value resistors, one between +OUT and
+OUTFILTERED and the other between –OUT and –OUTFILTERED (Figure 7). These resistors are in parallel with the
internal 25Ω resistor, lowering the overall resistance and
increasing filter bandwidth. To double the filter bandwidth,
for example, add two external 25Ω resistors to lower
the series resistance to 12.5Ω. The 36pF of capacitance
remains unchanged, so filter bandwidth doubles.
LT1993-2
8 –OUT
VEE
25Ω
25Ω
12pF
12pF
12pF
7 –OUTFILTERED
12pF
12pF
FILTERED OUTPUT
(87.5MHz)
25Ω
6 +OUTFILTERED
12pF
12pF
VEE
5 +OUT
19932 F08
Figure 8. LT1993-2 Internal Filter Topology Modified for
1/2x Filter Bandwidth (3 External Capacitors)
Bandpass filtering is also easily implemented with just a
few external components. An additional 120pF and 39nH,
each added differentially between +OUTFILTERED and
–OUTFILTERED creates a bandpass filter with a 71MHz
center frequency, –3dB points of 55MHz and 87MHz, and
1.6dB of insertion loss (Figure 9).
7 –OUTFILTERED
FILTERED OUTPUT
(350MHz)
12pF
25Ω
LT1993-2
VEE
6 +OUTFILTERED
12pF
25Ω
25Ω
8 –OUT
12pF
7 –OUTFILTERED
VEE
5 +OUT
19932 F07
Figure 7. LT1993-2 Internal Filter Topology Modified for
2x Filter Bandwidth (2 External Resistors)
12pF
39nH
FILTERED OUTPUT
120pF (71MHz BANDPASS,
–3dB @ 55MHz/87MHz)
25Ω
6 +OUTFILTERED
12pF
To decrease filter bandwidth, add two external capacitors,
one from +OUTFILTERED to ground, and the other from
–OUTFILTERED to ground. A single differential capacitor
connected between +OUTFILTERED and –OUTFILTERED
can also be used, but since it is being driven differentially
16
VEE
5 +OUT
19932 F09
Figure 9. LT1993-2 Output Filter Topology Modified for Bandpass
Filtering (1 External Inductor, 1 External Capacitor)
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19932fa
LT1993-2
U
U
W
U
APPLICATIO S I FOR ATIO
Output Common Mode Adjustment
The LT1993-2’s output common mode voltage is set by the
VOCM pin. It is a high-impedance input, capable of setting
the output common mode voltage anywhere in a range
from 1.1V to 3.6V. Bandwidth of the VOCM pin is typically
300MHz, so for applications where the VOCM pin is tied to
a DC bias voltage, a 0.1µF capacitor at this pin is recommended. For best distortion performance, the voltage at
the VOCM pin should be between 1.8V and 2.6V.
When interfacing with most ADCs, there is generally a
VOCM output pin that is at about half of the supply voltage
of the ADC. For 5V ADCs such as the LTC17XX family, this
VOCM output pin should be connected directly (with the
addition of a 0.1µF capacitor) to the input VOCM pin of the
LT1993-2. For 3V ADCs such as the LTC22XX families,
the LT1993-2 will function properly using the 1.65V from
the ADC’s VCM reference pin, but improved Spurious Free
Dynamic Range (SFDR) and distortion performance can
be achieved by level-shifting the LTC22XX’s VCM reference
voltage up to at least 1.8V. This can be accomplished as
shown in Figure 10 by using a resistor divider between
the LTC22XX’s VCM output pin and VCC and then bypassing the LT1993-2’s VOCM pin with a 0.1µF capacitor. For a
common mode voltage above 1.9V, AC coupling capacitors
are recommended between the LT1993-2 and LTC22XX
11k
1.9V
13
14
–INB
–INA
VOCM
+OUTFILTERED
0.1µF
31 1.5V
6
LT1993-2
15
IF IN
16
–OUTFILTERED
+INB
4.02k
2
10Ω
1
7
VCM
AIN+
LTC22xx
10Ω
2
AIN–
+INA
80.6Ω
19932 F10
Figure 10. Level Shifting 3V ADC VCM Voltage for
Improved SFDR
Large Output Voltage Swings
The LT1993-2 has been designed to provide the 3.2VP-P
output swing needed by the LTC1748 family of 14-bit
low-noise ADCs. This additional output swing improves
system SNR by up to 4dB. Typical performance curves
and AC specifications have been included for these applications.
Input Bias Voltage and Bias Current
The input pins of the LT1993-2 are internally biased to
the voltage applied to the VOCM pin. No external biasing
resistors are needed, even for AC-coupled operation. The
input bias current is determined by the voltage difference
between the input common mode voltage and the VOCM pin
(which sets the output common mode voltage). At both
the positive and negative inputs, any voltage difference is
imposed across 200Ω, generating an input bias current.
For example, if the inputs are tied to 2.5V with the VOCM
pin at 2.2V, then a total input bias current of 1.5mA will
flow into the LT1993-2’s +INA and +INB pins. Furthermore,
an additional input bias current totaling 1.5mA will flow
into the –INA and –INB inputs.
Application (Demo) Boards
3V
0.1µF
ADCs because of the input voltage range constraints of
the ADC.
The DC800A Demo Board has been created for stand-alone
evaluation of the LT1993-2 with either single-ended or
differential input and output signals. As shown, it accepts
a single-ended input and produces a single-ended output
so that the LT1993-2 can be evaluated using standard
laboratory test equipment. For more information on this
Demo Board, please refer to the Demo Board section of
this data sheet.
There are also additional demo boards available that
combine the LT1993-2 with a variety of different Linear
Technology ADCs. Please contact the factory for more
information on these demo boards.
www.BDTIC.com/Linear
19932fa
17
LT1993-2
U
TYPICAL APPLICATIO
18
www.BDTIC.com/Linear
19932fa
LT1993-2
U
PACKAGE DESCRIPTIO
UD Package
16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691)
0.70 ±0.05
3.50 ± 0.05
1.45 ± 0.05
2.10 ± 0.05 (4 SIDES)
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 ± 0.10
(4 SIDES)
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.20 TYP
OR 0.25 × 45° CHAMFER
R = 0.115
TYP
0.75 ± 0.05
15
16
PIN 1
TOP MARK
(NOTE 6)
0.40 ± 0.10
1
1.45 ± 0.10
(4-SIDES)
2
(UD16) QFN 0904
0.200 REF
0.00 – 0.05
NOTE:
1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
www.BDTIC.com/Linear
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.
0.25 ± 0.05
0.50 BSC
19932fa
19
LT1993-2
U
TYPICAL APPLICATIO
Demo Circuit DC800A Schematic
(AC Test Circuit)
R18
0Ω
R17
0Ω
VCC
VCC
GND
VCC
1
SW1
TP1
ENABLE
2
3
R16
0Ω
2
C17
1000pF
1
2
1
C18
0.01µF
1
1
J1
–IN
T1
5 1:4 Z-RATIO
4
MINICIRCUITS
TCM 4-19
14
2
C1
0.1µF
R5
0Ω
16
2
R3
[1]
9
VCCB VEEB
–INB
–OUT
–INA
–OUTFILTERED
+INB
+OUTFILTERED
+INA
VCCC
1
VCC
C10 2
0.01µF
1
10
ENABLE
VOCM
VCCA
+OUT
VEEA
2
3
4
2
C12
1000pF
C9 2
1000pF
1
1
C4
0.1µF
R10
8 24.9Ω
7
LT1993-2
15
3
VCC
11
VEEC
+6dB
2
1
R1
1Ω
13
C21
0.1µF
1
•
•
0dB
R6
0Ω
2
1
J2
+IN
12
C2
0.1µF
6
5
1
R8
[1]
R7
[1]
R9
24.9Ω
L1
[1]
1
C11
[1]
2
R14
0Ω
R12
75Ω
2
J4
–OUT
T2
3 1:4 Z-RATIO 4
2
C8
[1]
1
R15
[1]
+10.8dB
+6dB
2
1
C3
0.1µF
1
R11
75Ω
MINI5
0dB
CIRCUITS
TCM 4-19
J5
+OUT
2
1
VCC
2
1
•
R4
[1]
•
R2
0Ω
2
C16
[1]
2
1
C22
0.1µF
R13
[1]
C13
0.01µF
R19
14k
J6
TEST IN
1
T3
1:4
5
1
1
2
•
•
TP2
VCC
C5
0.1µF
C19, 0.1µF
1
4 MINICIRCUITS
TCM 4-19
C7
0.01µF
R21
[1]
2
C6
0.1µF
2
R22
[1]
4
J7
TEST OUT
2
1
2
1
3
1
T4
4:1
3
C20, 0.1µF
2
•
2
R20
11k
•
J3
VOCM
MINI5
CIRCUITS
TCM 4-19
VCC
1
2
1
TP3
GND
C14
4.7µF
2
1
C15
1µF
NOTES: UNLESS OTHERWISE SPECIFIED,
[1] DO NOT STUFF.
1
19932 TA02
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1993-4
900MHz Differential Amplifier/ADC Driver
AV = 4V/V, NF = 14.5dB, OIP3 = 40dBm at 70MHz
LT1993-10
700MHz Differential Amplifier/ADC Driver
AV = 10V/V, NF = 12.7dB, OIP3 = 40dBm at 70MHz
LT5514
Ultralow Distortion IF Amplifier/ADC Driver
Digitally Controlled Gain Output IP3 47dBm at 100MHz
LT6600-2.5
Very Low Noise Differential Amplifier and
2.5MHz Lowpass Filter
86dB S/N with 3V Supply, SO-8 Package
LT6600-5
Very Low Noise Differential Amplifier and
5MHz Lowpass Filter
82dB S/N with 3V Supply, SO-8 Package
LT6600-10
Very Low Noise Differential Amplifier and
10MHz Lowpass Filter
82dB S/N with 3V Supply, SO-8 Package
LT6600-20
Very Low Noise Differential Amplifier and
20MHz Lowpass Filter
76dB S/N with 3V Supply, SO-8 Package
Corporation
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20 Linear Technology
19932fa
LT/LT 1005 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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© LINEAR TECHNOLOGY CORPORATION 2005