lt1993-2 noise differential amplifier/ adc driver (av = 2v
TRANSCRIPT
LT1993-2
1Rev B
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TYPICAL APPLICATION
FEATURES DESCRIPTION
APPLICATIONS
800MHz Low Distortion, Low Noise Differential Amplifier/
ADC Driver (AV = 2V/V)
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 12-bit 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 trans-former or AC-coupling capacitors in many applications.
The LT1993-2 is designed to meet the demanding require-ments of communications transceiver applications. It can be used as a differential ADC driver, a general-purpose differential gain block, or in any other application requir-ing 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.
n Differential ADC Driver for: Imaging Communications
n Differential Driver/Receivern Single Ended to Differential Conversionn Differential to Single Ended Conversionn Level Shiftingn IF Sampling Receiversn SAW Filter Interfacing/Buffering
n 800MHz –3dB Bandwidthn Fixed Gain of 2V/V (6dB)n Low Distortion:
38dBm OIP3, –70dBc HD3 (70MHz, 2VP-P) 51dBm OIP3, –94dBc HD3 (10MHz, 2VP-P)
n Low Noise: 12.3dB NF, en = 3.8nV/√Hz (70MHz)n Differential Inputs and Outputsn Additional Filtered Outputsn Adjustable Output Common Mode Voltagen DC- or AC-Coupled Operationn Minimal Support Circuitry Requiredn Small 0.75mm Tall 16-Lead 3 × 3 QFN Package
4-Channel WCDMA Receive Channel
••
2.2V19932 TA01a
MINI-CIRCUITSTCM4-19
1:4Z-RATIO
LTC2255 125Msps14-BIT ADC SAMPLING
AT 92.16Msps
70MHzIF IN
52.3pF82nH0.1µF
0.1µF
12.2Ω
LT1993-2
–INA
–INB
–OUTFILTERED
–OUT
+OUTFILTERED
+OUT+INB
+INA VOCMENABLE
12.2Ω
LTC2255ADC
AIN–
AIN+
FREQUENCY (MHz)0
AMPL
ITUD
E (d
BFS)
0
–20
–40
–80
–60
–100
–10
–30
–50
–90
–70
–110
–120
19932 TA01b
15105 20 25 4530 35 40
32768 POINT FFTTONE CENTER FREQUENCIESAT 62.5MHz, 67.5MHz, 72.5MHz, 77.5MHz
4-Tone WCDMA Waveform, LT1993-2 Driving LTC2255 14-Bit
ADC at 92.16Msps
All registered trademarks and trademarks are the property of their respective owners.
LT1993-2
2Rev B
For more information www.analog.com
DC ELECTRICAL CHARACTERISTICS
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) ............ ±45mAOutput Short Circuit Duration (Note 2) ............ IndefiniteOperating Temperature Range (Note 3) ....–40°C to 85°CSpecified Temperature Range (Note 4) ....–40°C to 85°CStorage Temperature Range .................. –65°C to 125°CJunction Temperature ........................................... 125°CLead Temperature Range (Soldering 10 sec)......... 300°C
(Note 1)
The l 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 Gain Differential (+OUT, –OUT), VIN = ±0.8V Differential l 5.8 6.08 6.3 dB
VSWINGMIN Single-Ended +OUT, –OUT, +OUTFILTERED, –OUTFILTERED. VIN = ±2.2V Differential
l
0.25 0.35 0.5
V V
VSWINGMAX Single-Ended +OUT, –OUT, +OUTFILTERED, –OUTFILTERED. VIN = ±2.2V Differential
l
3.6 3.5
3.75 V V
VSWINGDIFF Output Voltage Swing Differential (+OUT, –OUT), VIN = ±2.2V Differential
l
6.5 6
7 VP-P VP-P
IOUT Output Current Drive (Note 5) l ±40 ±45 mA
VOS Input Offset Voltage
l
–6.5 –10
1 6.5 10
mV mV
TCVOS Input Offset Voltage Drift TMIN to TMAX l 2.5 µV/°C
IVRMIN Input Voltage Range, MIN Single-Ended l –0.1 V
IVRMAX Input Voltage Range, MAX Single-Ended l 5.1 V
RINDIFF Differential Input Resistance l 170 200 240
PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
ORDER INFORMATIONLEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT1993CUD-2#PBF LT1993CUD-2#TRPBF LBJG 16-LEAD (3mm × 3mm) PLASTIC QFN –40°C to 85°C
LT1993IUD-2#PBF LT1993IUD-2#TRPBF LBJG 16-LEAD (3mm × 3mm) PLASTIC QFN –40°C to 85°C
Consult ADI Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
16 15 14 13
5 6 7 8
TOP VIEW
UD PACKAGE16-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 125°C, θJA = 68°C/W, θJC = 4.2°C/WEXPOSED PAD IS VEE (PIN 17) MUST BE SOLDERED TO THE PCB
9
1017VEE
11
12
4
3
2
1VCCC
VOCM
VCCA
VEEA
VEEC
ENABLE
VCCB
VEEB
+INA
+INB
–INA
–INB
+OUT
+OUT
FILT
ERED
–OUT
FILT
ERED
–OUT
LT1993-2
3Rev B
For more information www.analog.com
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Input/Output Characteristics
–3dBBW –3dB Bandwidth 200mVP-P Differential (+OUT, –OUT) 500 800 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)
4 ns
tON Turn-On Time 40 ns
tOFF Turn-Off Time 250 ns
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
CINDIFF Differential Input Capacitance 1 pF
CMRR Common Mode Rejection Ratio Input Common Mode –0.1V to 5.1V l 45 70 dB
ROUTDIFF Output Resistance 0.3
COUTDIFF Output Capacitance 0.8 pF
Common Mode Voltage Control (VOCM Pin)
GCM Common Mode Gain Differential (+OUT, –OUT), VOCM = 1.1V to 3.6V Differential (+OUT, –OUT), VOCM = 1.3V to 3.4V
l
0.9 0.9
1 1.1 1.1
V/V V/V
VOCMMIN Output Common Mode Voltage Adjustment Range, MIN
Measured Single-Ended at +OUT and –OUT
l
1.1 1.3
V V
VOCMMAX Output Common Mode Voltage Adjustment Range, MAX
Measured Single-Ended at +OUT and –OUT
l
3.6 3.4
V V
VOSCM Output Common Mode Offset Voltage Measured from VOCM to Average of +OUT and –OUT l –30 4 30 mV
IBIASCM VOCM Input Bias Current l 5 15 µA
RINCM VOCM Input Resistance l 0.8 3 M
CINCM VOCM Input Capacitance 1 pF
ENABLE Pin
VIL ENABLE Input Low Voltage l 0.8 V
VIH ENABLE Input High Voltage l 2 V
IIL ENABLE Input Low Current ENABLE = 0.8V l 0.5 µA
IIH ENABLE Input High Current ENABLE = 2V l 1 3 µA
Power Supply
VS Operating Range l 4 5 5.5 V
IS Supply Current ENABLE = 0.8V l 88 100 112 mA
ISDISABLED Supply Current (Disabled) ENABLE = 2V l 250 500 µA
PSRR Power Supply Rejection Ratio 4V to 5.5V l 55 90 dB
The l 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.
DC ELECTRICAL CHARACTERISTICS
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.
LT1993-2
4Rev B
For more information www.analog.com
AC ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
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
Noise/Harmonic Performance Input/output Characteristics
1kHz Signal
Second/Third Harmonic Distortion 2VP-P Differential (+OUTFILTERED, –OUTFILTERED) –100 dBc
2VP-P Differential (+OUT, –OUT) –100 dBc
2VP-P Differential (+OUT, –OUT), RL = 100 –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 = 100 –91 dBc
Third-Order IMD 2VP-P Differential Composite (+OUTFILTERED, –OUTFILTERED), f1 = 0.95kHz, f2 = 1.05kHz
–102 dBc
2VP-P Differential Composite (+OUT, –OUT), RL = 100 , f1 = 0.95kHz, f2 = 1.05kHz
–102 dBc
3.2VP-P Differential Composite (+OUTFILTERED, –OUTFILTERED), f1 = 0.95kHz, f2 = 1.05kHz
–93 dBc
OIP31k Output Third-Order Intercept Differential (+OUTFILTERED, –OUTFILTERED), f1 = 0.95kHz, f2 = 1.05kHz
54 dBm
en1k Input Referred Noise Voltage Density 3.5 nV/√Hz
1dB Compression Point RL = 100 22.7 dBm
10MHz Signal
Second/Third Harmonic Distortion 2VP-P Differential (+OUTFILTERED, –OUTFILTERED) –94 dBc
2VP-P Differential (+OUT, –OUT) –94 dBc
2VP-P Differential (+OUT, –OUT), RL = 100 –86 dBc
3.2VP-P Differential (+OUTFILTERED, –OUTFILTERED) –85 dBc
3.2VP-P Differential (+OUT, –OUT) –85 dBc
3.2VP-P Differential (+OUT, –OUT), RL = 100 –77 dBc
Third-Order IMD 2VP-P Differential Composite (+OUTFILTERED, –OUTFILTERED), f1 = 9.5MHz, f2 = 10.5MHz
–96 dBc
2VP-P Differential Composite (+OUT, –OUT), RL = 100 , f1 = 9.5MHz, f2 = 10.5MHz
–96 dBc
3.2VP-P Differential Composite (+OUTFILTERED, –OUTFILTERED), f1 = 9.5MHz, f2 = 10.5MHz
–87 dBc
OIP310M Output Third-Order Intercept Differential (+OUTFILTERED, –OUTFILTERED), f1 = 9.5MHz, f2 = 10.5MHz
51 dBm
NF Noise Figure Measured Using DC800A Demo Board 11.3 dB
en10M Input Referred Noise Voltage Density 3.5 nV/√Hz
1dB Compression Point RL = 100 22.6 dBm
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.
LT1993-2
5Rev B
For more information www.analog.com
AC ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
50MHz Signal
Second/Third Harmonic Distortion 2VP-P Differential (+OUTFILTERED, –OUTFILTERED) –77 dBc
2VP-P Differential (+OUT, –OUT) –77 dBc
2VP-P Differential (+OUT, –OUT), RL = 100 –74 dBc
3.2VP-P Differential (+OUTFILTERED, –OUTFILTERED) –68 dBc
3.2VP-P Differential (+OUT, –OUT) –65 dBc
3.2VP-P Differential (+OUT, –OUT), RL = 100 –65 dBc
Third-Order IMD 2VP-P Differential Composite (+OUTFILTERED, –OUTFILTERED), f1 = 49.5MHz, f2 = 50.5MHz
–84 dBc
2VP-P Differential Composite (+OUT, –OUT), RL = 100 , f1 = 49.5MHz, f2 = 50.5MHz
–88 dBc
3.2VP-P Differential Composite (+OUTFILTERED, –OUTFILTERED), f1 = 49.5MHz, f2 = 50.5MHz
–75 dBc
OIP350M Output Third-Order Intercept Differential (+OUTFILTERED, –OUTFILTERED), f1 = 49.5MHz, f2 = 50.5MHz
45 dBm
NF Noise Figure Measured Using DC800A Demo Board 11.8 dB
en50M Input Referred Noise Voltage Density 3.65 nV/√Hz
1dB Compression Point RL = 100 19.7 dBm
70MHz Signal
Second/Third Harmonic Distortion 2VP-P Differential (+OUTFILTERED, –OUTFILTERED) –70 dBc
2VP-P Differential (+OUT, –OUT) –61 dBc
2VP-P Differential (+OUT, –OUT), RL = 100 –61 dBc
Third-Order IMD 2VP-P Differential Composite (+OUTFILTERED, –OUTFILTERED), f1 = 69.5MHz, f2 = 70.5MHz
–70 dBc
2VP-P Differential Composite (+OUT, –OUT), RL = 100 , f1 = 69.5MHz, f2 = 70.5MHz
–72 dBc
OIP370M Output Third-Order Intercept Differential (+OUTFILTERED, –OUTFILTERED), f1 = 69.5MHz, f2 = 70.5MHz
38 dBm
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 = 100 18.5 dBm
100MHz Signal
Second/Third Harmonic Distortion 2VP-P Differential (+OUTFILTERED, –OUTFILTERED) –56 dBc
2VP-P Differential (+OUT, –OUT) –54 dBc
2VP-P Differential (+OUT, –OUT), RL = 100 –51 dBc
Third-Order IMD 2VP-P Differential Composite (+OUTFILTERED, –OUTFILTERED), f1 = 99.5MHz, f2 = 100.5MHz
–58 dBc
2VP-P Differential Composite (+OUT, –OUT), RL = 100 , f1 = 99.5MHz, f2 = 100.5MHz
–59 dBc
OIP3100M Output Third-Order Intercept Differential (+OUTFILTERED, –OUTFILTERED), f1 = 99.5MHz, f2 = 100.5MHz
32 dBm
NF Noise Figure Measured Using DC800A Demo Board 12.8 dB
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.
LT1993-2
6Rev B
For more information www.analog.com
FREQUENCY (MHz)0
THIR
D OR
DER
IMD
(dBc
)
–10
–20
–30
–50
–40
–60
–70
–80
–90
–100
–110
19932 G06
604020 80 100 140120
2 TONES, 2VP-P COMPOSITE1MHz TONE SPACING
UNFILTERED OUTPUTS
FILTERED OUTPUTS
FREQUENCY (MHz)0
THIR
D OR
DER
IMD
(dBc
)
–10
–20
–30
–50
–40
–60
–70
–80
–90
–100
–110
19932 G04
604020 80 100 140120
UNFILTERED OUTPUTS
FILTERED OUTPUTS
2 TONES, 2VP-P COMPOSITE1MHz TONE SPACING
FREQUENCY (MHz)
GAIN
(dB)
21
18
15
12
9
6
3
0
–31 100 1000 10000
19932 G03
10
VIN = 100mVP-PUNFILTERED OUTPUTS
10pF5pF2pF0pF
FREQUENCY (MHz)
GAIN
(dB)
12
9
6
3
0
–3
–6
–9
–121 100 1000 10000
19932 G01
10
VIN = 100mVP-PUNFILTERED: RLOAD = 400ΩFILTERED: RLOAD = 350Ω (EXTERNAL) +50Ω (INTERNAL, FILTERED OUTPUTS)
UNFILTERED OUTPUTS
FILTERED OUTPUTS
FREQUENCY (MHz)
GAIN
(dB)
12
9
6
3
0
–3
–6
–9
–121 100 1000 10000
19932 G02
10
VIN = 100mVP-PUNFILTERED: RLOAD = 100ΩFILTERED: RLOAD = 50Ω (EXTERNAL) +50Ω (INTERNAL, FILTERED OUTPUTS)
UNFILTERED OUTPUTS
FILTERED OUTPUTS
FREQUENCY (MHz)0
THIR
D OR
DER
IMD
(dBc
)
–10
–20
–30
–50
–40
–60
–70
–80
–90
–100
–110
19932 G05
604020 80 100 140120
2 TONES, 2VP-P COMPOSITE1MHz TONE SPACING
UNFILTERED OUTPUTS
FILTERED OUTPUTS
Frequency Response RLOAD = 400
Frequency Response RLOAD = 100
Frequency Response vs CLOAD, RLOAD = 400
Third Order Intermodulation Distortion vs Frequency Differential Input, No RLOAD
Third Order Intermodulation Distortion vs Frequency Differential Input, RLOAD = 400
Third Order Intermodulation Distortion vs Frequency Differential Input, RLOAD = 100
TYPICAL PERFORMANCE CHARACTERISTICS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime.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 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.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
en100M Input Referred Noise Voltage Density 4.1 nV/√Hz
1dB Compression Point RL = 100 17.8 dBm
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.
LT1993-2
7Rev B
For more information www.analog.com
FREQUENCY (MHz)1
DIST
ORTI
ON (d
Bc)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–11010 100 1000
19932 G15
UNFILTERED OUTPUTSVOUT = 2VP-P
HD3
HD2
FREQUENCY (MHz)1
DIST
ORTI
ON (d
Bc)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–11010 100 1000
19932 G14
UNFILTERED OUTPUTSVOUT = 2VP-P
HD3
HD2
FREQUENCY (MHz)1
DIST
ORTI
ON (d
Bc)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–11010 100 1000
19932 G13
UNFILTERED OUTPUTSVOUT = 2VP-P
HD3
HD2
FREQUENCY (MHz)1
DIST
ORTI
ON (d
Bc)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–11010 100 1000
19932 G12
FILTERED OUTPUTSVOUT = 2VP-P
HD3
HD2
FREQUENCY (MHz)1
DIST
ORTI
ON (d
Bc)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–11010 100 1000
19932 G10
FILTERED OUTPUTSVOUT = 2VP-P
HD3
HD2
FREQUENCY (MHz)1
DIST
ORTI
ON (d
Bc)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–11010 100 1000
19932 G11
FILTERED OUTPUTSVOUT = 2VP-P
HD3
HD2
FREQUENCY (MHz)0
OUTP
UT IP
3 (d
Bm)
60
55
50
40
45
35
30
25
20
19932 G08
604020 80 100 140120
2 TONES, 2VP-P COMPOSITE1MHz TONE SPACING
UNFILTERED OUTPUTS
FILTERED OUTPUTS
FREQUENCY (MHz)0
OUTP
UT IP
3 (d
Bm)
60
55
50
40
45
35
30
25
20
19932 G09
604020 80 100 140120
2 TONES, 2VP-P COMPOSITE1MHz TONE SPACING
UNFILTERED OUTPUTS
FILTERED OUTPUTS
FREQUENCY (MHz)0
OUTP
UT IP
3 (d
Bm)
60
55
50
40
45
35
30
25
20
19932 G07
604020 80 100 140120
2 TONES, 2VP-P COMPOSITE1MHz TONE SPACING
UNFILTERED OUTPUTS
FILTERED OUTPUTS
Output Third Order Intercept vs Frequency, Differential Input, No RLOAD
Output Third Order Intercept vs Frequency, Differential Input, RLOAD = 400
Output Third Order Intercept vs Frequency, Differential Input, RLOAD = 100
Distortion (Filtered) vs Frequency Differential Input, No RLOAD
Distortion (Filtered) vs Frequency Differential Input, RLOAD = 400
Distortion (Filtered) vs Frequency Differential Input, RLOAD = 100
Distortion (Unfiltered) vs Frequency, Differential Input, No RLOAD
Distortion (Unfiltered) vs Frequency, Differential Input, RLOAD = 400
Distortion (Unfiltered) vs Frequency, Differential Input, RLOAD = 100
TYPICAL PERFORMANCE CHARACTERISTICS
LT1993-2
8Rev B
For more information www.analog.com
FREQUENCY (MHz)1
DIST
ORTI
ON (d
Bc)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–11010 100 1000
19932 G22
HD3
HD2
UNFILTERED OUTPUTSVOUT = 2VP-P
FREQUENCY (MHz)1
DIST
ORTI
ON (d
Bc)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–11010 100 1000
19932 G24
HD3
HD2
UNFILTERED OUTPUTSVOUT = 2VP-P
FREQUENCY (MHz)1
DIST
ORTI
ON (d
Bc)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–11010 100 1000
19932 G23
HD3
HD2
UNFILTERED OUTPUTSVOUT = 2VP-P
FREQUENCY (MHz)1
DIST
ORTI
ON (d
Bc)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–11010 100 1000
19932 G20
FILTERED OUTPUTSVOUT = 2VP-P
HD3
HD2
FREQUENCY (MHz)1
DIST
ORTI
ON (d
Bc)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–11010 100 1000
19932 G19
FILTERED OUTPUTSVOUT = 2VP-P
HD3
HD2
FREQUENCY (MHz)1
DIST
ORTI
ON (d
Bc)
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–11010 100 1000
19932 G21
FILTERED OUTPUTSVOUT = 2VP-P
HD3
HD2
Distortion (Filtered) vs Frequency Single-Ended Input, No RLOAD
Distortion (Filtered) vs Frequency Single-Ended Input, RLOAD = 400
Distortion (Filtered) vs Frequency Single-Ended Input, RLOAD = 100
Distortion (Unfiltered) vs Frequency, Single-Ended Input, No RLOAD
Distortion (Unfiltered) vs Frequency, Single-Ended Input, RLOAD = 400
Distortion (Unfiltered) vs Frequency, Single-Ended Input, RLOAD = 100
TYPICAL PERFORMANCE CHARACTERISTICS
OUTPUT AMPLITUDE (dBm)–1
DIST
ORTI
ON (d
Bc)
–50
–55
–60
–70
–65
–75
–80
–85
–90
–95
–100
19932 G18
531 7 9 11
HD3 UNFILTERED OUTPUTS
HD2 UNFILTERED OUTPUTS
HD2 FILTERED OUTPUTS
HD3 FILTERED OUTPUTS
OUTPUT AMPLITUDE (dBm)–1
DIST
ORTI
ON (d
Bc)
–50
–55
–60
–70
–65
–75
–80
–85
–90
–95
–100
19932 G16
531 7 9 11
HD3 UNFILTERED OUTPUTS
HD2 FILTERED OUTPUTS
HD2 UNFILTERED OUTPUTS
HD3 FILTERED OUTPUTS
OUTPUT AMPLITUDE (dBm)–1
DIST
ORTI
ON (d
Bc)
–50
–55
–60
–70
–65
–75
–80
–85
–90
–95
–100
19932 G17
531 7 9 11
HD3 UNFILTERED OUTPUTS
HD3 FILTERED OUTPUTS
HD2 UNFILTERED OUTPUTS
HD2 FILTERED OUTPUTS
Distortion vs Output Amplitude 70MHz Differential Input, No RLOAD
Distortion vs Output Amplitude 70MHz Differential Input, RLOAD = 400
Distortion vs Output Amplitude 70MHz Differential Input, RLOAD = 100
LT1993-2
9Rev B
For more information www.analog.com
FREQUENCY (MHz)10
INPU
T RE
FERR
ED N
OISE
VOL
TAGE
(nV/
Hz) 12
6
4
8
10
2
0100 1000
19932 G30
FREQUENCY (MHz)10
NOIS
E FI
GURE
(dB)
25
20
15
10
5
0100 1000
19932 G29
VCC = 5VMEASURED USING DC800A DEMO BOARD
FREQUENCY (MHz)1
OUTP
UT 1
dB C
OMPR
ESSI
ON (d
Bm)
30
25
20
15
10
5
0
–5
–1010 100 1000
19932 G28
RLOAD = 400Ω
RLOAD = 100Ω
UNFILTERED OUTPUTS
OUTPUT AMPLITUDE (dBm)–1
DIST
ORTI
ON (d
Bc)
–50
–55
–60
–70
–65
–75
–80
–85
–90
–95
–100
19932 G27
531 7 9 11
HD3 UNFILTERED OUTPUTS
HD2 UNFILTERED OUTPUTS
HD2 FILTERED OUTPUTS
HD3 FILTERED OUTPUTS
OUTPUT AMPLITUDE (dBm)–1
DIST
ORTI
ON (d
Bc)
–50
–55
–60
–70
–65
–75
–80
–85
–90
–95
–100
19932 G26
531 7 9 11
HD3 UNFILTERED OUTPUTS
HD2 UNFILTERED OUTPUTS
HD3 FILTERED OUTPUTS
HD2 FILTERED OUTPUTS
OUTPUT AMPLITUDE (dBm)–1
DIST
ORTI
ON (d
Bc)
–50
–55
–60
–70
–65
–75
–80
–85
–90
–95
–100
19932 G25
531 7 9 11
HD3 UNFILTERED OUTPUTS
HD2 UNFILTERED OUTPUTS
HD3 FILTERED OUTPUTS
HD2 FILTERED OUTPUTS
Distortion vs Output Amplitude 70MHz Single-Ended Input, No RLOAD
Distortion vs Output Amplitude 70MHz Single-Ended Input, RLOAD = 400
Distortion vs Output Amplitude 70MHz Single-Ended Input, RLOAD = 100
Output 1dB Compression vs Frequency Noise Figure vs Frequency
Input Referred Noise Voltage vs Frequency
TYPICAL PERFORMANCE CHARACTERISTICS
FREQUENCY (MHz)
ISOL
ATIO
N (d
B)
–40
–50
–60
–70
–80
–90
–100
–1101 100 1000 10000
19932 G31
10
UNFILTERED OUTPUTS
FREQUENCY (MHz)1
INPU
T IM
PEDA
NCE
(MAG
NITU
DE Ω
, PHA
SE°) 300
250
200
150
100
50
0
–50
–10010 100 1000
19932 G32
IMPEDANCE MAGNITUDE
IMPEDANCE PHASE
FREQUENCY (MHz)1
0.1
OUTP
UT IM
PEDA
NCE
(Ω)
1
10
100
10 100 1000
19932 G33
UNFILTERED OUTPUTS
Isolation vs FrequencyDifferential Input Impedance vs Frequency
Differential Output Impedance vs Frequency
LT1993-2
10Rev B
For more information www.analog.com
OUTPUT COMMON MODE VOLTAGE (V)1.2
DIST
ORTI
ON (d
Bc)
–64
–66
–68
–72
–70
–74
–76
19932 G40
1.81.61.4 2.0 2.2 2.62.4
FILTERED OUTPUTS, NO RLOADVOUT = 70MHz 2VP-P
HD3
HD2
TIME (ns)0
VOLT
AGE
(V) 1
2
500 625
19932 G41
4
2
–2125 250 375
0
4
3
0
+OUT
–OUT
ENABLE
RLOAD = 100Ω PER OUTPUT
TIME (ns)0
OUTP
UT V
OLTA
GE (V
)
2.0
2.5
3.0
225200 250
19932 G39
1.5
1.0
050 100 150 17525 75 125
0.5
4.0
3.5 +OUT
–OUT
RLOAD = 100ΩPER OUTPUT
TIME (ns)0
OUTP
UT V
OLTA
GE (V
)
2.2
2.4
2.6
4540 50
19932 G38
2.0
1.8
1.410 20 30 355 15 25
1.6
3.0
2.8
RLOAD = 100Ω PER OUTPUT
TIME (ns)0
OUTP
UT V
OLTA
GE (V
)
2.20
2.22
2.24
4540 50
19932 G37
2.18
2.16
2.1210 20 30 355 15 25
2.14
2.28
2.26
RLOAD = 100Ω PER OUTPUT
TIME (ns)0
VOLT
AGE
(V) 1
2
500 625
19932 G42
4
2
–2125 250 375
0
4
3
0
+OUT
–OUT
ENABLE
RLOAD = 100Ω PER OUTPUT
Small-Signal Transient Response Large-Signal Transient Response Overdrive Recovery Time
Distortion vs Output Common Mode Voltage LT1993-2 Driving LTC2249 14-Bit ADC Turn-On Time Turn-Off Time
TYPICAL PERFORMANCE CHARACTERISTICS
FREQUENCY (MHz)1
PSRR
, CM
RR (d
B)
100
90
80
70
60
50
40
30
20
10
010 100 1000
19932 G36
CMRR
PSRR
UNFILTERED OUTPUTS
FREQUENCY (MHz)10
INPU
T RE
FLEC
TION
COE
FFIC
IENT
(S11
)
0
–5
–50
–45
–40
–35
–30
–25
–20
–15
–10
100 1000
19932 G34
MEASURED USING DC800A DEMO BOARD
FREQUENCY (MHz)10
OUTP
UT R
EFLE
CTIO
N CO
EFFI
CIEN
T (S
22)
0
–5
–50
–45
–40
–35
–30
–25
–20
–15
–10
100 1000
19932 G35
MEASURED USING DC800A DEMO BOARD
Input Reflection Coefficient vs Frequency
Output Reflection Coefficient vs Frequency PSRR, CMRR vs Frequency
LT1993-2
11Rev B
For more information www.analog.com
FREQUENCY (MHz)0
AMPL
ITUD
E (d
BFS)
10 20 30 40
19932 G46
–120
–110
–100
–80
–60
–40
–20
–90
–70
–50
–30
–10
0
5 15 25 35
8192 POINT FFTfIN = 30MHz, –1dBFSFILTERED OUTPUTS
FREQUENCY (MHz)0
AMPL
ITUD
E (d
BFS)
10 20 30 40
19932 G47
–120
–110
–100
–80
–60
–40
–20
–90
–70
–50
–30
–10
0
5 15 25 35
8192 POINT FFTfIN = 50MHz, –1dBFSFILTERED OUTPUTS
FREQUENCY (MHz)0
AMPL
ITUD
E (d
BFS)
10 20 30 40
19932 G49
–120
–110
–100
–80
–60
–40
–20
–90
–70
–50
–30
–10
0
5 15 25 35
32768 POINT FFTTONE 1 AT 69.5MHz, –7dBFSTONE 2 AT 70.5MHz, –7dBFSFILTERED OUTPUTS
FREQUENCY (MHz)0
AMPL
ITUD
E (d
BFS)
10 20 30 40
19932 G48
–120
–110
–100
–80
–60
–40
–20
–90
–70
–50
–30
–10
0
5 15 25 35
8192 POINT FFTfIN = 70MHz, –1dBFSFILTERED OUTPUTS
0
–20
–40
–80
–60
–100
–10
–30
–50
–90
–70
–110
–120
FREQUENCY (MHz)0
AMPL
ITUD
E (d
BFS)
19932 G50
15105 20 25 4530 35 40
32768 POINT FFTTONE CENTER FREQUENCIESAT 67.5MHz, 72.5MHz
0
–20
–40
–80
–60
–100
–10
–30
–50
–90
–70
–110
–120
FREQUENCY (MHz)0
AMPL
ITUD
E (d
BFS)
19932 G51
15105 20 25 4530 35 40
32768 POINT FFTTONE CENTER FREQUENCIESAT 62.5MHz, 67.5MHz, 72.5MHz, 77.5MHz
30MHz 8192 Point FFT, LT1993-2 Driving LTC2249 14-Bit ADC
50MHz 8192 Point FFT, LT1993-2 Driving LTC2249 14-Bit ADC
70MHz 8192 Point FFT, LT1993-2 Driving LTC2249 14-Bit ADC
70MHz 2-Tone 32768 Point FFT, LT1993-2 Driving LTC2249 14-Bit ADC
2-Tone WCDMA Waveform, LT1993-2 Driving LTC2255 14-Bit ADC at 92.16Msps
4-Tone WCDMA Waveform, LT1993-2 Driving LTC2255 14-Bit ADC at 92.16Msps
TYPICAL PERFORMANCE CHARACTERISTICS
LT1993-2
12Rev B
For more information www.analog.com
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 sup-plies 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 out-put voltage at these pins is set to the voltage applied at VOCM.
+OUTFILTERED, –OUTFILTERED (Pins 6, 7): Filtered Outputs. These pins add a series 25 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 AC-coupled. 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 AC-coupled. 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.
PIN FUNCTIONS
LT1993-2
13Rev B
For more information www.analog.com
+
–14
–INA
5
+OUT
19932 BD3VCCA
10VCCB
1VCCC
11ENABLE
13
–INB
12pFVCCA
A
VEEA
VEEA
200Ω
200Ω
200Ω
200Ω
25Ω
200Ω
6
+OUTFILTERED
–
+16
+INA
8
–OUT
15
+INB
VCCB
B
VEEB
VEEB
200Ω
200Ω
25Ω
200Ω
12pF
12pF
7
–OUTFILTERED
12VEEC
9VEEB
4VEEA
+
–VEEC
C
VCCC
2
VOCM
BIAS
BLOCK DIAGRAM
LT1993-2
14Rev B
For more information www.analog.com
Circuit Description
The LT1993-2 is a low-noise, low-distortion differential amplifier/ADC driver with:
• DC to 800MHz –3dB bandwidth
• Fixed gain of 2V/V (6dB) independent of RLOAD
• 200 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 closed-loop topology which incorporates 3 internal ampli-fiers. 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 200 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 out-put 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.
Input Impedance and Matching Networks
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 200 (differential); when driven single-ended, the input impedance is 133 .
For single-ended 50 applications, an 80.6 shunt match-ing resistor to ground will result in the proper input termi-nation (Figure 1). For differential inputs there are several termination options. If the input source is 50 differen-tial, then input matching can be accomplished by either a 67 shunt resistor across the inputs (Figure 3), or a 33 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 addi-tional 6dB of gain (Figure 4). With a 1:4 impedance ratio transformer, ideal matching impedance at the transformer output is 200 , so no termination resistors are required to match the LT1993-2’s 200 input impedance.
19932 F01
IF IN
0.1µFLT1993-2
–INA
–INB–OUT
+OUT
8
5
+INB
+INA
14
13
15
80.6ΩZIN = 50ΩSINGLE-ENDED
16
Figure 1. Input Termination for Single-Ended 50 Input Impedance
Figure 2. Input Termination for Differential 50 Input Impedance
19932 F02
IF IN–
IF IN+
LT1993-2
–INA
–INB–OUT
+OUT
8
5+INB
+INA
14
13
15
33Ω
ZIN = 50ΩDIFFERENTIAL
16
33Ω
APPLICATIONS INFORMATION
LT1993-2
15Rev B
For more information www.analog.com
Single-Ended to Differential Operation
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 differ-entially without any voltage swing needed from amplifier C. Single-ended to differential conversion using more conventional topologies suffers from performance lim-itations due to the common mode amplifier.
Driving ADCs
The LT1993-2 has been specifically designed to inter-face 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 filter-ing 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 high impedance inputs of these differ-ential ADCs. If the filtered outputs are used, then cutoff frequency and the type of filter can be tailored for the specific application if needed.
Wideband Applications (Using the +OUT and –OUT Pins)
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; there-fore, 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 10 and 25 gives excellent results.
Figure 3. Alternate Input Termination for Differential 50 Input Impedance
Figure 4. Input Termination for Differential 50 Input Impedance with 6dB Additional Gain
19932 F02
IF IN–
IF IN+
LT1993-2
–INA
–INB–OUT
+OUT
8
5+INB
+INA
14
13
15
ZIN = 50ΩDIFFERENTIAL
16
67Ω
19932 F04
0.1µFLT1993-2
–INA
–INB–OUT
+OUT
8
5
+INB
+INA
14
13
15
ZIN = 50ΩDIFFERENTIAL
1:4 TRANSFORMER(MINI-CIRCUITS TCM4-19)
16
19932 F05
LT1993-2
–OUT
+OUT
8
5
10Ω TO 25Ω
10Ω TO 25Ω
ADC
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 low-pass filter network with a –3dB bandwidth of 175MHz (Figure 6). These pins each have an output impedance of 25 . Internal capacitances are 12pF to VEE on each filtered output, plus an additional 12pF capacitor con-nected differentially between the two filtered outputs. This resistor/capacitor combination creates filtered outputs
APPLICATIONS INFORMATION
LT1993-2
16Rev B
For more information www.analog.com
that look like a series 25 resistor with a 36pF capacitor shunting each filtered output to AC ground, giving a –3dB bandwidth of 175MHz.
it will appear at each filtered output as a single-ended capacitance of twice the value. To halve the filter band-width, 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).
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 25 resistor, lowering the overall resis-tance and increasing filter bandwidth. To double the filter bandwidth, for example, add two external 25 resistors to lower the series resistance to 12.5 . The 36pF of capac-itance remains unchanged, so filter bandwidth doubles.
Figure 6. LT1993-2 Internal Filter Topology –3dB BW ≈175MHz
Figure 7. LT1993-2 Internal Filter Topology Modified for 2x Filter Bandwidth (2 External Resistors)
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).
Figure 8. LT1993-2 Internal Filter Topology Modified for 1/2x Filter Bandwidth (3 External Capacitors)
19932 F06
25Ω
VEE
VEE
12pF
LT1993-2–OUT
+OUT
25Ω
12pF
12pF
–OUTFILTERED
+OUTFILTERED
8
7
6
5
FILTERED OUTPUT(175MHz)
VEE
VEE
19932 F07
25Ω
25Ω
12pF
LT1993-2–OUT
+OUT
25Ω
25Ω
12pF
12pF
–OUTFILTERED
FILTERED OUTPUT(350MHz)
+OUTFILTERED
8
7
6
5
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
VEE
VEE
19932 F08
25Ω
12pF
LT1993-2–OUT
+OUT
25Ω
12pF
12pF
12pF
12pF
12pF
–OUTFILTERED
+OUTFILTERED
8
7
6
5
FILTERED OUTPUT(87.5MHz)
Figure 9. LT1993-2 Output Filter Topology Modified for Bandpass Filtering (1 External Inductor, 1 External Capacitor)
VEE
VEE
19932 F09
25Ω
12pF
LT1993-2–OUT
+OUT
25Ω
12pF
12pF
120pF39nH
–OUTFILTERED
+OUTFILTERED
8
7
6
5
FILTERED OUTPUT(71MHz BANDPASS,–3dB @ 55MHz/87MHz)
APPLICATIONS INFORMATION
LT1993-2
17Rev B
For more information www.analog.com
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 fami-lies, 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 ref-erence voltage up to at least 1.8V. This can be accom-plished 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 capaci-tor. For a common mode voltage above 1.9V, AC coupling capacitors are recommended between the LT1993-2 and LTC22XX ADCs because of the input voltage range con-straints of the ADC.
Large Output Voltage Swings
The LT1993-2 has been designed to provide the 3.2VP-Poutput 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 differ-ence is imposed across 200 , 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.
VOCM and Output Voltages for Proper Operation
The electrical tables suggest 1.3V VOCM minimum to ensure proper operation over temperature. The electrical tables also guarantee VSWINGMIN to be 0.5V over tem-perature. It would appear that operation is okay so long as the low output voltage on either pin is 0.5V or higher, and VOCM is 1.3V or higher. The values in the table are correct. However, the VSWINGMIN value is tested with the input difference overdriven. Overdriven input is a static condition during which the overdrive forces transistors well into their saturated state.
Amplifier Inputs
Dynamically, the situation is more complicated. Referring to the Block Diagram, an NPN differential pair with tail current forms the input stage of both amplifiers A and B. Appropriate biasing of these inputs requires 1.3V, or in other words the same value as the minimum VOCM.
19932 F10
IF IN
LT1993-2
–INA
–INBVOCM
231
6
7
1
2+INB
+INA
14
13
15
80.6Ω
16
10Ω
10Ω LTC22xx0.1µF
0.1µF
+OUTFILTERED
–OUTFILTERED
AIN+
AIN–
4.02k
11k
1.9V
1.5V
3V
VCM
Figure 10. Level Shifting 3V ADC VCM Voltage for Improved SFDR
APPLICATIONS INFORMATION
LT1993-2
18Rev B
For more information www.analog.com
Specifically, the minimum voltage at amplifiers A and B should be 1.3V.
The calculation for the voltage at the A and B inputs is as follows.
Amp A CMINA •RR1 RR
VOCM •1
1 RR
Amp B CM–INB •RR
1 RRVOCM •
11 RR
RRRFRG
Gain2
Amplifier Outputs
The Amplifiers A and B output from the collectors of pull-down NPNs in combination with high-side cur-rent boosting NPN emitters. The pull-down NPN circuit includes degeneration resistors. Fully linear, non-satu-rated operation requires that the NPN collector voltage be 0.8V or higher. As a result, operation without compro-mised stability must be to 0.8V output voltages or higher. This requirement is at variance with the electrical table VSWINGMIN; again, VSWINGMIN uses input overdrive in a static condition, whereas full-speed operation demands non-saturated, full Beta transistors.
The following table shows examples of operating condi-tion voltages. The boldface numbers indicate examples that do one or more of the following:
• Amplifier input voltage is at the minimum suggested as noted above.
• Output voltage low level is 0.8V as noted above.
• Output voltage high level is at 3.5V (data sheet VSWINGMAX).
Table 1.
Gain 2 2
VOCM 1.3 2.5
–INA/–INB 1.3 3
+INA/+INB 1.8 2
VINDIFF 0.5 –1
RR 1 1
Amp CM A 1.55 2.25
Amp CM B 1.3 2.75
+VOUT 1.8 1.5
–VOUT 0.8 3.5
Application (Demo) Boards
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 stan-dard 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.
APPLICATIONS INFORMATION
LT1993-2
19Rev B
For more information www.analog.com
TYPICAL APPLICATION
LT1993-2
20Rev B
For more information www.analog.com
3.00 ±0.10(4 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1.45 ±0.05(4 SIDES)
NOTE:1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2)2. DRAWING NOT TO SCALE3. ALL DIMENSIONS ARE IN MILLIMETERS4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE5. EXPOSED PAD SHALL BE SOLDER PLATED6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
PIN 1TOP MARK(NOTE 6)
0.40 ±0.10
BOTTOM VIEW—EXPOSED PAD
1.45 ± 0.10(4-SIDES)
0.75 ±0.05 R = 0.115TYP
0.25 ±0.05
1
PIN 1 NOTCH R = 0.20 TYPOR 0.25 × 45° CHAMFER
15 16
2
0.50 BSC
0.200 REF
2.10 ±0.053.50 ±0.05
0.70 ±0.05
0.00 – 0.05
(UD16) QFN 0904
0.25 ±0.050.50 BSC
PACKAGE OUTLINE
UD Package16-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1691 Rev Ø)
PACKAGE DESCRIPTION
LT1993-2
21Rev B
For more information www.analog.com
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
REVISION HISTORYREV DATE DESCRIPTION PAGE NUMBER
B 09/18 Adding operating description for VOCM and output. 17, 18
(Revision history begins at Rev B)
LT1993-2
22Rev B
For more information www.analog.com ANALOG DEVICES, INC. 2005-2018
D17142-0-9/18(B)www.analog.com
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
•• C20, 0.1µF
••
VCC
C144.7µF
C151µF
• •
J6TEST IN
J7TEST OUT
J3VOCM
• •
3
1
241
5
VCC
VCCC10
0.01µFC9
1000pF
19932 TA02
13
14
15
16
11 10 912
VCC
VCCGND
SW1
2 3 41
8
7
6
5
R8[1]
R1024.9Ω
R60Ω
R180Ω
R50Ω
R7[1]
R924.9Ω
R1275Ω
R160Ω
R15[1] +6dB
R1175Ω
+6dB
C180.01µF
NOTES: UNLESS OTHERWISE SPECIFIED,[1] DO NOT STUFF.
C40.1µF
C30.1µF
C20.1µF
C10.1µF
T11:4 Z-RATIO
MINI-CIRCUITSTCM 4-19
MINI-CIRCUITSTCM 4-19
MINI-CIRCUITSTCM 4-19
T21:4 Z-RATIO
C171000pF
C130.01µF
C121000pF
R22[1]
R21[1]
C70.01µF
–INA
–INB
+INB
+INA
VEEC VCCB VEEB
VOCM VCCAVCCC VEEA
–OUTFILTERED
–OUT
+OUTFILTERED
+OUT
ENABLE
TP1ENABLE
R140Ω
J4–OUT
J5+OUT
R13[1]
5
4
2
2
1 3
3
R4[1]
R3[1]
R20Ω
J1–IN
J2+IN
R11Ω
0dB
R2011k
R1914k
R170Ω
VCCVCC
TP2VCC
C50.1µF
C60.1µF
T44:1
5
43
1
2
TP3GND
LT1993-2
1
2
1
2
1
2
1
21
21
C210.1µF
21
1T31:45
4
2
3
C19, 0.1µF
21 21
21
21
2
1
2
1
2
1
2
1
2
1
C8[1]
L1[1]
2
1
C11[1]
1
2
2
1
1
1
C220.1µF
2
1
C16[1]
1
2
21
21
+10.8dB
0dBMINI-
CIRCUITSTCM 4-19
Demo Circuit DC800A Schematic(AC Test Circuit)
RELATED PARTS
TYPICAL APPLICATION