features descriptio u - analog devices · 2020. 2. 1. · 1 ltc1744 1744f 14-bit, 50msps adc sample...
TRANSCRIPT
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LTC1744
1744f
14-Bit, 50Msps ADC
■ Sample Rate: 50Msps■ 77dB SNR and 87dB SFDR (3.2V Range)■ 73.5dB SNR and 90dB SFDR (2V Range)■ No Missing Codes■ Single 5V Supply■ Power Dissipation: 1.2W■ Selectable Input Ranges: ±1V or ±1.6V■ 150MHz Full Power Bandwidth S/H■ Pin Compatible Family
25Msps: LTC1746 (14 Bit), LTC1745 (12 Bit)50Msps: LTC1744 (14 Bit), LTC1743 (12 Bit)65Msps: LTC1742 (14 Bit), LTC1741 (12 Bit)80Msps: LTC1748 (14 Bit), LTC1747 (12 Bit)
■ 48-Pin TSSOP Package
■ Telecommunications■ Receivers■ Base Stations■ Spectrum Analysis■ Imaging Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
OF
14-BITPIPELINED ADC
14S/H
CIRCUIT
±1V DIFFERENTIAL
ANALOG INPUT
AIN+
AIN–
SENSE
VCM
4.7µF
DIFF AMP
REFLA REFHB
GND
1744 BD
ENC4.7µF
0.1µF0.1µF1µF 1µF
REFHAREFLB
BUFFER
RANGESELECT
2.5VREF
CORRECTIONLOGIC AND
SHIFTREGISTER
OUTPUTLATCHES
CONTROL LOGIC
OVDD
VDD
OGND
0.5V TO 5V
5V
0.1µF
1µF 1µF 1µF
D13
D0CLKOUT
•••
ENC
DIFFERENTIALENCODE INPUT
OEMSBINV
0.1µF
The LTC®1744 is a 50Msps, sampling 14-bit A/D con-verter designed for digitizing high frequency, wide dynamicrange signals. Pin selectable input ranges of ±1V and ±1.6Valong with a resistor programmable mode allow theLTC1744’s input range to be optimized for a wide varietyof applications.
The LTC1744 is perfect for demanding communicationsapplications with AC performance that includes 77dBSNR and 87dB spurious free dynamic range. Ultralow jitterof 0.3psRMS allows undersampling of IF frequencies withexcellent noise performance. DC specs include ±4LSBmaximum INL and no missing codes over temperature.
The digital interface is compatible with 5V, 3V and 2V logicsystems. The ENC and ENC inputs may be driven differen-tially from PECL, GTL and other low swing logic families orfrom single-ended TTL or CMOS. The low noise, high gainENC and ENC inputs may also be driven by a sinusoidalsignal without degrading performance. A separate outputpower supply can be operated from 0.5V to 5V, making iteasy to connect directly to any low voltage DSPs or FIFOs.
The TSSOP package with a flow-through pinout simplifiesthe board layout.
50Msps, 14-Bit ADC with a ±1V Differential Input Range
DESCRIPTIO
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FEATURES
APPLICATIO SU
BLOCK DIAGRA
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LTC1744
1744f
PARAMETER CONDITIONS MIN TYP MAX UNITS
Resolution (No Missing Codes) ● 14 Bits
Integral Linearity Error (Note 6) ● – 4 ±1 4 LSBDifferential Linearity Error ● –1 ±0.5 1.5 LSBOffset Error (Note 7) – 20 ±5 20 mVGain Error External Reference (SENSE = 1.6V) –3 ±1 3 %FSFull-Scale Tempco IOUT(REF) = 0 ±40 ppm/°C
ORDER PARTNUMBER
OVDD = VDD (Notes 1, 2)Supply Voltage (VDD) ................................................ 6VAnalog Input Voltage (Note 3) .... –0.3V to (VDD + 0.3V)Digital Input Voltage (Note 4) ..... –0.3V to (VDD + 0.3V)Digital Output Voltage ................. –0.3V to (VDD + 0.3V)OGND Voltage ..............................................–0.3V to 1VPower Dissipation ............................................ 2000mWOperating Temperature Range
LTC1744C ............................................... 0°C to 70°CLTC1744I ............................................ – 40°C to 85°C
Storage Temperature Range ................. –65°C to 150°CLead Temperature (Soldering, 10 sec).................. 300°C
LTC1744CFWLTC1744IFW
TJMAX = 150°C, θJA = 35°C/W
Consult factory for parts specified with wider operating temperature ranges.
The ● indicates specifications which apply over the full operatingtemperature range, otherwise specifications are at TA = 25°C. (Note 5)
ABSOLUTE MAXIMUM RATINGS
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PACKAGE/ORDER INFORMATION
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101112131415161718192021222324
TOP VIEW
FW PACKAGE48-LEAD PLASTIC TSSOP
484746454443424140393837363534333231302928272625
SENSEVCMGNDAIN
+
AIN–
GNDVDDVDDGND
REFLBREFHA
GNDGND
REFLAREFHB
GNDVDDVDDGNDVDDGND
MSBINVENCENC
OFOGNDD13D12D11OVDDD10 D9D8D7OGNDGNDGNDD6D5D4OVDDD3D2D1D0OGNDCLKOUTOE
CO VERTER CHARACTERISTICS
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SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Analog Input Range (Note 8) 4.75V ≤ VDD ≤ 5.25V ● ±1 to ±1.6 VIIN Analog Input Leakage Current 10 nA
CIN Analog Input Capacitance Sample Mode ENC < ENC 15 pFHold Mode ENC > ENC 8 pF
tACQ Sample-and-Hold Acquisition Time ● 7.5 9.5 ns
tAP Sample-and-Hold Acquisition Delay Time 0 ns
tJITTER Sample-and-Hold Acquisition Delay Time Jitter 0.3 psRMSCMRR Analog Input Common Mode Rejection Ratio 1.0V < (AIN– = AIN+) < 3.5V 80 dB
The ● indicates specifications which apply over the full operating temperature range, otherwisespecifications are at TA = 25°C. (Note 5)A ALOG I PUT
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LTC1744
1744f
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
SNR Signal-to-Noise Ratio 5MHz Input Signal (2V Range) 73.5 dBFS5MHz Input Signal (3.2V Range) ● 75.5 77 dBFS
25MHz Input Signal (2V Range) 72.5 dBFS25MHz Input Signal (3.2V Range) 75.5 dBFS
70MHz Input Signal (2V Range) 70 dBFS70MHz Input Signal (3.2V Range) 71.5 dBFS
SFDR Spurious Free Dynamic Range 5MHz Input Signal (2V Range) 92 dB5MHz Input Signal (3.2V Range) ● 76 87 dB
25MHz Input Signal (2V Range) 87 dB25MHz Input Signal (3.2V Range) 79 dB
70MHz Input Signal (2V Range) 73 dB70MHz Input Signal (3.2V Range) 66 dB
S/(N + D) Signal-to-(Noise + Distortion) Ratio 5MHz Input Signal (2V Range) 73 dBFS5MHz Input Signal (3.2V Range) ● 73 76 dBFS
25MHz Input Signal (2V Range) 72.5 dBFS25MHz Input Signal (3.2V Range) 73.5 dBFS
70MHz Input Signal (2V Range) 68 dBFS70MHz Input Signal (3.2V Range) 64 dBFS
THD Total Harmonic Distortion 5MHz Input Signal, First 5 Harmonics (2V Range) – 90 dB5MHz Input Signal, First 5 Harmonics (3.2V Range) – 85 dB
25MHz Input Signal, First 5 Harmonics (2V Range) – 85 dB25MHz Input Signal, First 5 Harmonics (3.2V Range) – 78 dB
70MHz Input Signal, First 5 Harmonics (2V Range) – 72 dB70MHz Input Signal, First 5 Harmonics (3.2V Range) – 65 dB
IMD Intermodulation Distortion fIN1 = 2.52MHz, fIN2 = 5.2MHz (2V Range) – 90 dBcfIN1 = 2.52MHz, fIN2 = 5.2MHz (3.2V Range) – 80 dBc
Sample-and-Hold Bandwidth RSOURCE = 50Ω 150 MHz
PARAMETER CONDITIONS MIN TYP MAX UNITS
VCM Output Voltage IOUT = 0 2.42 2.5 2.58 V
VCM Output Tempco IOUT = 0 ±30 ppm/°CVCM Line Regulation 4.75V ≤ VDD ≤ 5.25V 3 mV/VVCM Output Resistance 1mA ≤ IOUT ≤ 1mA 4 Ω
The ● indicates specifications which apply over the full operating temperature range,otherwise specifications are at TA = 25°C. AIN = –1dBFS. (Note 5)DY A IC ACCURACY
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(Note 5)I TER AL REFERE CE CHARACTERISTICSU U U
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LTC1744
1744f
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITSfSAMPLE(MAX) Maximum Sampling Frequency ● 50 MHzt1 ENC Low Time (Note 9) ● 9.5 10 1000 nst2 ENC High Time (Note 9) ● 9.5 10 1000 nst3 Aperture Delay of Sample-and-Hold 0 nst4 ENC to Data Delay CL = 10pF (Note 8) ● 1.4 4.5 8 nst5 ENC to CLKOUT Delay CL = 10pF (Note 8) ● 0.5 2.3 5 nst6 CLKOUT to Data Delay CL = 10pF (Note 8) ● 0 2.2 nst7 DATA Access Time After OE ↓ CL = 10pF (Note 8) 10 25 nst8 BUS Relinquish Time (Note 8) 10 25 ns
Data Latency 5 cycles
The ● indicates specifications which apply over the full operating temperaturerange, otherwise specifications are at TA = 25°C. (Note 5)TI I G CHARACTERISTICS
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Note 1: Absolute Maximum Ratings are those values beyond which the lifeof a device may be impaired.Note 2: All voltage values are with respect to ground with GND(unless otherwise noted).Note 3: When these pin voltages are taken below GND or above VDD, theywill be clamped by internal diodes. This product can handle input currentsof greater than 100mA below GND or above VDD without latchup.Note 4: When these pin voltages are taken below GND, they will beclamped by internal diodes. This product can handle input currents of>100mA below GND without latchup. These pins are not clamped to VDD.
Note 5: VDD = 5V, fSAMPLE = 50MHz, differential ENC/ENC = 2VP-P 50MHzsine wave, input range = ±1.6V differential, unless otherwise specified.Note 6: Integral nonlinearity is defined as the deviation of a code from astraight line passing through the actual endpoints of the transfer curve.The deviation is measured from the center of the quantization band.Note 7: Bipolar offset is the offset voltage measured from – 0.5 LSBwhen the output code flickers between 00 0000 0000 0000 and 111111 1111 1111.Note 8: Guaranteed by design, not subject to test.Note 9: Recommended operating conditions.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VDD Positive Supply Voltage 4.75 5.25 V
IDD Positive Supply Current ● 245 300 mA
PDIS Power Dissipation ● 1.2 1.5 W
OVDD Digital Output Supply Voltage 0.5 VDD V
The ● indicates specifications which apply over the full operating temperaturerange, otherwise specifications are at TA = 25°C. (Note 5)POWER REQUIRE E TS
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SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIH High Level Input Voltage VDD = 5.25V ● 2.4 V
VIL Low Level Input Voltage VDD = 4.75V ● 0.8 V
IIN Digital Input Current VIN = 0V to VDD ● ±10 µACIN Digital Input Capacitance MSBINV and OE Only 1.5 pF
VOH High Level Output Voltage OVDD = 4.75V IO = –10µA 4.74 V
IO = –200µA ● 4 VVOL Low Level Output Voltage OVDD = 4.75V IO = 160µA 0.05 V
IO = 1.6mA ● 0.1 0.4 V
IOZ Hi-Z Output Leakage D13 to D0 VOUT = 0V to VDD, OE = High ● ±10 µACOZ Hi-Z Output Capacitance D13 to D0 OE = High (Note 8) ● 15 pF
ISOURCE Output Source Current VOUT = 0V – 50 mA
ISINK Output Sink Current VOUT = 5V 50 mA
The ● indicates specifications which apply over the fulloperating temperature range, otherwise specifications are at TA = 25°C. (Note 5)DIGITAL I PUTS A D DIGITAL OUTPUTS
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LTC1744
1744f
TYPICAL PERFOR A CE CHARACTERISTICS
UW
CODE0 4000 8000 12000 16000
INL
ERRO
R (L
SB)
1744 G01
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
TA = 25°C
CODE0 4000 8000 12000 16000
DNL
ERRO
R (L
SB)
1744 G02
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
TA = 25°C
FREQUENCY (MHz)0
25.37
AMPL
ITUD
E (d
BFS)
1744 G03
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.02 4 6 8 10 12 14 16 18 20 22 24
TA = 25°C
Typical INL, 3.2V Range Typical DNL, 3.2V Range
Nonaveraged, 8192 Point FFT,Input Frequency = 2.5MHz, –1dB,2V Range
Nonaveraged, 8192 Point FFT,Input Frequency = 20MHz, –1dB,2V Range
Nonaveraged, 8192 Point FFT,Input Frequency = 2.5MHz, –1dB,3.2V Range
Nonaveraged, 8192 Point FFT,Input Frequency = 20MHz, –1dB,3.2V Range
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G04
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G05
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G06
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
Averaged, 8192 Point 2-Tone FFT,Input Frequency = 2.5MHz and5.2MHz, 2V Range
Averaged, 8192 Point 2-Tone FFT,Input Frequency = 2.5MHz and5.2MHz, 3.2V Range
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G07
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G08
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
(Note 5)
Averaged, 8192 Point FFT, InputFrequency = 2.5MHz, –6dB,2V Range
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G10
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
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LTC1744
1744f
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Averaged, 8192 Point FFT, InputFrequency = 2.5MHz, –20dB,3.2V Range
Averaged, 8192 Point FFT, InputFrequency = 20MHz, –6dB,2V Range
Averaged, 8192 Point FFT, InputFrequency = 20MHz, –6dB,3.2V Range
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G13
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G14
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G15
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
Averaged, 8192 Point FFT, InputFrequency = 20MHz, –20dB,2V Range
Averaged, 8192 Point FFT, InputFrequency = 20MHz, –20dB,3.2V Range
Averaged, 8192 Point FFT, InputFrequency = 51MHz, –1dB,2V Range
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G16
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
TA = 25°C
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G17
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G18
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
Averaged, 8192 Point FFT, InputFrequency = 2.5MHz, –6dB,3.2V Range
Averaged, 8192 Point FFT, InputFrequency = 2.5MHz, –20dB,2V Range
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G11
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G12
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
(Note 5)
Averaged, 8192 Point FFT, InputFrequency = 51MHz, –6dB,2V Range
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G19
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
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LTC1744
1744f
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Averaged, 8192 Point FFT, InputFrequency = 51MHz, –20dB,2V Range
Averaged, 8192 Point FFT, InputFrequency = 70MHz, – 1dB,2V Range
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G20
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C TA = 25°C
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G21
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
Averaged, 8192 Point FFT, InputFrequency = 70MHz, –6dB,2V Range
Averaged, 8192 Point FFT, InputFrequency = 70MHz, –20dB,2V Range
SNR vs Sample Rate, InputFrequency = 5MHz, –1dB
TA = 25°C
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G22
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
TA = 25°C
FREQUENCY (MHz)0 2 4 6 8 10 12 14 16 18 20 22 24
25.37
AMPL
ITUD
E (d
BFS)
1744 G23
0.5
–10.0
–20.0
–30.0
–40.0
–50.0
–60.0
–70.0
–80.0
–90.0
–100.0
–110.0
–120.0
SAMPLE RATE (Msps)0 20 40 60 80 100
SNR
(dBF
S)
1744 G24
78
77
76
75
74
73
72
71
70
69
68
2V RANGE
3.2V RANGE
TA = 25°C
SFDR vs Sample Rate, InputFrequency = 5MHz, –1dB
SAMPLE RATE (Msps)0 20 40 60 80 100
SFDR
(dBc
)
1744 G25
100
95
90
85
80
75
70
65
60
55
50
2V RANGE
3.2V RANGE
TA = 25°C
(Note 5)
Grounded Input Histogram
CODE8152 8153 8154 8155 8156 8157 8158
COUN
T
1744 G09
40000
35000
30000
25000
20000
15000
10000
5000
0
TA = 25°C
SNR vs Input Frequency andAmplitude, 3.2V Range
INPUT FREQUENCY (MHz)1
SNR
(dBc
)
80
75
70
65
60
55
5010 100
1744 G31
–1dBFS
–6dBFS
–20dBFS
TA = 25°C
INPUT FREQUENCY (MHz)1
SNR
(dBc
)
75
70
65
60
55
5010 100
1744 G30
–1dBFS
–6dBFS
–20dBFS
TA = 25°C
TA = 25°C
SNR vs Input Frequency andAmplitude, 2V Range
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LTC1744
1744f
TYPICAL PERFOR A CE CHARACTERISTICS
UW
(Note 5)
SAMPLE RATE (Msps)0
POW
ER (m
W)
1050
1075
1100
30 50
1744 G35
1025
1000
97510 20 40
1125
1150
1175TA = 25°C
Power Dissipation vs Sample Rate
SFDR vs Input Frequency andAmplitude, 2V Range
SFDR vs Input Frequency andAmplitude, 3.2V Range
INPUT FREQUENCY (MHz)1
SFDR
(dBF
S)
120
110
100
90
80
70
6010 100
1744 G32
–1dBFS
–6dBFS
–20dBFSTA = 25°C
INPUT FREQUENCY (MHz)1
SFDR
(dBF
S)
120
110
100
90
80
70
6010 100
1744 G33
–1dBFS
–6dBFS
–20dBFSTA = 25°C
INPUT FREQUENCY (MHz)1
AMPL
ITUD
E (d
Bc)
–60
–70
–80
–90
–100
–110
–12010 100
1744 G29
TA = 25°C
Worst Harmonic 4th or Higher vsInput Frequency, 3.2V Range, –1dB
INPUT FREQUENCY (MHz)1
AMPL
ITUD
E (d
Bc)
–60
–70
–80
–90
–100
–11010 100
1744 G28
3rd HARMONIC
2nd HARMONIC
TA = 25°C
2nd and 3rd Harmonic vs InputFrequency, 3.2V Range, –1dB
2nd and 3rd Harmonic vs InputFrequency, 2V Range, –1dB
Worst Harmonic 4th or Higher vsInput Frequency, 2V Range, –1dB
INPUT FREQUENCY (MHz)1
AMPL
ITUD
E (d
Bc)
–60
–70
–80
–90
–100
–11010 100
1744 G26
3rd HARMONIC
2nd HARMONIC
TA = 25°C
INPUT FREQUENCY (MHz)1
AMPL
ITUD
E (d
Bc)
–60
–70
–80
–90
–100
–11010 100
1744 G27
TA = 25°C
INPUT AMPLITUDE (dBFS)
SFDR
(dBc
AND
dBF
S)
110
100
90
80
70
60
50
40
1744 G34
–60 –40 –20 0
SFDR dBFS
SFDR dBc
TA = 25°C
SFDR vs Input Amplitude, 2VRange, 5MHz Input Frequency
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LTC1744
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SENSE (Pin 1): Reference Sense Pin. Ground selects±1V. VDD selects ±1.6V. Greater than 1V and less than1.6V applied to the SENSE pin selects an input range of±VSENSE, ±1.6V is the largest valid input range.VCM (Pin 2): 2.5V Output and Input Common Mode Bias.Bypass to ground with 4.7µF ceramic chip capacitor.GND (Pins 3, 6, 9, 12, 13, 16, 19, 21, 36, 37): ADCPower Ground.AIN+ (Pin 4): Positive Differential Analog Input.AIN– (Pin 5): Negative Differential Analog Input.VDD (Pins 7, 8, 17, 18, 20): 5V Supply. Bypass to AGNDwith 1µF ceramic chip capacitor.REFLB (Pin 10): ADC Low Reference. Bypass to Pin 11 with0.1µF ceramic chip capacitor. Do not connect to Pin␣ 14.REFHA (Pin 11): ADC High Reference. Bypass to Pin 10 with0.1µF ceramic chip capacitor, to Pin 14 with a 4.7µF ceramiccapacitor and to ground with 1µF ceramic capacitor.REFLA (Pin 14): ADC Low Reference. Bypass to Pin 15 with0.1µF ceramic chip capacitor, to Pin 11 with a 4.7µF ceramiccapacitor and to ground with 1µF ceramic capacitor.REFHB (Pin 15): ADC High Reference. Bypass to Pin 14 with0.1µF ceramic chip capacitor. Do not connect to Pin␣ 11.
PI FU CTIO S
UUU
MSBINV (Pin 22): MSB Inversion Control. Low invertsthe MSB, 2’s complement output format. High does notinvert the MSB, offset binary output format.ENC (Pin 23): Encode Input. The input sample starts onthe positive edge.ENC (Pin 24): Encode Complement Input. Conversionstarts on the negative edge. Bypass to ground with 0.1µFceramic for single-ended encode signal.OE (Pin 25): Output Enable. Low enables outputs. Logichigh makes outputs Hi-Z.CLKOUT (Pin 26): Data Valid Output. Latch data on therising edge of CLKOUT.OGND (Pins 27, 38, 47): Output Driver Ground.D0-D3 (Pins 28 to 31): Digital Outputs. D0 is the LSB.OVDD (Pins 32, 43): Positive Supply for the Output Driv-ers. Bypass to ground with 0.1µF ceramic chip capacitor.D4-D6 (Pins 33 to 35): Digital Outputs.D7-D10 (Pins 39 to 42): Digital Outputs.D11-D13 (Pins 44 to 46): Digital Outputs. D13 is the MSB.OF (Pin 48): Over/Under Flow Output. High when an overor under flow has occurred.
TYPICAL PERFOR A CE CHARACTERISTICS
UW
(Note 5)
FREQUENCY (MHz)0
AMPL
ITUD
E (d
B)
–60
–30
0.5–10–20
–40–50
–70–80
–100–110
–130–140
8 1624.99
1744 G36
–90
–120
–1502 4 6 10 12 14 18 20 22 24
TA = 25°C
FREQUENCY (MHz)0
AMPL
ITUD
E (d
B)
–60
–30
0.5–10–20
–40–50
–70–80
–100–110
–130–140
8 1624.99
1744 G37
–90
–120
–1502 4 6 10 12 14 18 20 22 24
TA = 25°C
Input = 5MHz, –25dBFS, No DitherInput = 5MHz, –25dBFS,Dither Applied
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10
LTC1744
1744f
OF
14-BITPIPELINED ADC
14S/H
CIRCUIT
±1V DIFFERENTIAL
ANALOG INPUT
AIN+
AIN–
SENSE
VCM
4.7µF
DIFF AMP
REFLA REFHB
GND
1744 BD
ENC4.7µF
0.1µF0.1µF1µF 1µF
REFHAREFLB
BUFFER
RANGESELECT
2.5VREF
CORRECTIONLOGIC AND
SHIFTREGISTER
OUTPUTLATCHES
CONTROL LOGIC
OVDD
VDD
OGND
0.5V TO 5V
5V
0.1µF
1µF 1µF 1µF
D13
D0CLKOUT
•••
ENC
DIFFERENTIALENCODE INPUT
OEMSBINV
0.1µF
t4
1744 TD
t3
t6
t5 t5
N
t1t2
DATA (N – 5)DB13 TO DB0
ANALOGINPUT
ENCODE
DATA
CLKOUT
DATA (N – 4)DB13 TO DB0
DATA (N – 3)DB13 TO DB0
t7 t8
DATA NDB13 TO DB0, OF AND CLKOUT
OE
DATA
TI I G DIAGRAUW W
UU WFU CTIO AL BLOCK DIAGRA
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11
LTC1744
1744f
APPLICATIO S I FOR ATIO
WU UU
2, 3, etc. The 3rd order intermodulation products are 2fa+ fb, 2fb + fa, 2fa – fb and 2fb – fa. The intermodulationdistortion is defined as the ratio of the RMS value of eitherinput tone to the RMS value of the largest 3rd orderintermodulation product.
Spurious Free Dynamic Range (SFDR)
Spurious free dynamic range is the peak harmonic orspurious noise that is the largest spectral componentexcluding the input signal and DC. This value is expressedin decibels relative to the RMS value of a full scale inputsignal.
Input Bandwidth
The input bandwidth is that input frequency at which theamplitude of the reconstructed fundamental is reduced by3dB for a full scale input signal.
Aperture Delay Time
The time from when a rising ENC equals the ENC voltageto the instant that the input signal is held by the sample andhold circuit.
Aperture Delay Jitter
The variation in the aperture delay time from conversion toconversion. This random variation will result in noisewhen sampling an AC input. The signal to noise ratio dueto the jitter alone will be:
SNRJITTER = –20log (2π) • FIN • TJITTER
CONVERTER OPERATION
As shown in Figure 1, the LTC1744 is a CMOS pipelinedmultistep converter. The converter has four pipelinedADC stages; a sampled analog input will result in adigitized value five cycles later, see the Timing Diagramsection. The analog input is differential for improvedcommon mode noise immunity and to maximize the inputrange. Additionally, the differential input drive will reduceeven order harmonics of the sample-and-hold circuit. Theencode input is also differential for improved commonmode noise immunity.
DYNAMIC PERFORMANCE
Signal-to-Noise Plus Distortion Ratio
The signal-to-noise plus distortion ratio [S / (N + D)] is theratio between the RMS amplitude of the fundamental inputfrequency and the RMS amplitude of all other frequencycomponents at the ADC output. The output is band limitedto frequencies above DC to below half the samplingfrequency.
Signal-to-Noise Ratio
The signal-to-noise ratio (SNR) is the ratio between theRMS amplitude of the fundamental input frequency andthe RMS amplitude of all other frequency componentsexcept the first five harmonics and DC.
Total Harmonic Distortion
Total harmonic distortion is the ratio of the RMS sum of allharmonics of the input signal to the fundamental itself. Theout-of-band harmonics alias into the frequency bandbetween DC and half the sampling frequency. THD isexpressed as:
THD LogV V V Vn
V= + + +20 2 3 4
1
2 2 2 2...
where V1 is the RMS amplitude of the fundamental fre-quency and V2 through Vn are the amplitudes of thesecond through nth harmonics. The THD calculated in thisdata sheet uses all the harmonics up to the fifth.
Intermodulation Distortion
If the ADC input signal consists of more than one spectralcomponent, the ADC transfer function nonlinearity canproduce intermodulation distortion (IMD) in addition toTHD. IMD is the change in one sinusoidal input caused bythe presence of another sinusoidal input at a differentfrequency.
If two pure sine waves of frequencies fa and fb are appliedto the ADC input, nonlinearities in the ADC transferfunction can create distortion products at the sum anddifference frequencies of mfa ± nfb, where m and n = 0, 1,
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12
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1744f
APPLICATIO S I FOR ATIO
WU UUFigure 1. Block Diagram
DIFFREFAMP
REFBUF
4.7µF
1µF0.1µF 0.1µF
1µF
INTERNAL CLOCK SIGNALSREFL REFH
DIFFERENTIALINPUT
LOW JITTERCLOCKDRIVER
RANGESELECT
2.5VREFERENCE
5-BITPIPELINEDADC STAGE
FIRST STAGE
4-BITPIPELINEDADC STAGE
SECOND STAGE
4-BITPIPELINEDADC STAGE
THIRD STAGE
4-BITFLASHADC
FOURTH STAGE
ENCREFHAREFLB REFLA REFHB ENC
SHIFT REGISTERAND CORRECTION
OEMSBINV OGND
OF
OVDD 0.5V TO5V
D13
D0
CLKOUT
1744 F01
INPUTS/H
SENSE
VCM
AIN–
AIN+
4.7µF
OUTPUTDRIVERS
CONTROL LOGICAND
CALIBRATION LOGIC
•••
The LTC1744 has two phases of operation, determined bythe state of the differential ENC/ENC input pins. For brev-ity, the text will refer to ENC greater than ENC as ENC highand ENC less than ENC as ENC low.
Each pipelined stage shown in Figure 1 contains an ADC,a reconstruction DAC and an interstage residue amplifier.In operation, the ADC quantizes the input to the stage andthe quantized value is subtracted from the input by theDAC to produce a residue. The residue is amplified andoutput by the residue amplifier. Successive stages operateout of phase so that when the odd stages are outputtingtheir residue, the even stages are acquiring that residueand visa versa.
When ENC is low, the analog input is sampled differentiallydirectly onto the input sample-and-hold capacitors, insidethe “Input S/H” shown in the block diagram. At the instantthat ENC transitions from low to high, the sampled inputis held. While ENC is high, the held input voltage isbuffered by the S/H amplifier which drives the first pipelinedADC stage. The first stage acquires the output of the S/Hduring this high phase of ENC. When ENC goes back low,
the first stage produces its residue which is acquired bythe second stage. At the same time, the input S/H goesback to acquiring the analog input. When ENC goes backhigh, the second stage produces its residue which isacquired by the third stage. An identical process is re-peated for the third stage, resulting in a third stage residuethat is sent to the fourth stage ADC for final evaluation.
Each ADC stage following the first has additional range toaccommodate flash and amplifier offset errors. Resultsfrom all of the ADC stages are digitally delayed such thatthe results can be properly combined in the correctionlogic before being sent to the output buffer.
SAMPLE/HOLD OPERATION AND INPUT DRIVE
Sample Hold Operation
Figure 2 shows an equivalent circuit for the LTC1744CMOS differential sample-and-hold. The differential ana-log inputs are sampled directly onto sampling capacitors(CSAMPLE) through CMOS transmission gates. This directcapacitor sampling results in lowest possible noise for a
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APPLICATIO S I FOR ATIO
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given sampling capacitor size. The capacitors shownattached to each input (CPARASITIC) are the summation ofall other capacitance associated with each input.
During the sample phase when ENC/ENC is low, thetransmission gate connects the analog inputs to the sam-pling capacitors and they charge to and track the differen-tial input voltage. When ENC/ENC transitions from low tohigh the sampled input voltage is held on the samplingcapacitors. During the hold phase when ENC/ENC is highthe sampling capacitors are disconnected from the inputand the held voltage is passed to the ADC core forprocessing. As ENC/ENC transitions from high to low theinputs are reconnected to the sampling capacitors toacquire a new sample. Since the sampling capacitors stillhold the previous sample, a charging glitch proportional to
the change in voltage between samples will be seen at thistime. If the change between the last sample and the newsample is small the charging glitch seen at the input will besmall. If the input change is large, such as the change seenwith input frequencies near Nyquist, then a larger chargingglitch will be seen.
Common Mode Bias
The ADC sample-and-hold circuit requires differentialdrive to achieve specified performance. Each input shouldswing ±0.8V for the 3.2V range or ±0.5V for the 2V range,around a common mode voltage of 2.5V. The VCM outputpin (Pin 2) may be used to provide the common mode biaslevel. VCM can be tied directly to the center tap of atransformer to set the DC input level or as a reference levelto an op amp differential driver circuit. The VCM pin mustbe bypassed to ground close to the ADC with 4.7µF orgreater.
Input Drive Impedance
As with all high performance, high speed ADCs the dy-namic performance of the LTC1744 can be influenced bythe input drive circuitry, particularly the second and thirdharmonics. Source impedance and input reactance caninfluence SFDR. At the falling edge of encode the sample-and-hold circuit will connect the 7pF sampling capacitor tothe input pin and start the sampling period. The samplingperiod ends when encode rises, holding the sampled inputon the sampling capacitor. Ideally the input circuitryshould be fast enough to fully charge the sampling capaci-tor during the sampling period 1/(2FENCODE); however,this is not always possible and the incomplete settling maydegrade the SFDR. The sampling glitch has been designedto be as linear as possible to minimize the effects ofincomplete settling.
For the best performance, it is recomended to have asource impedence of 100Ω or less for each input. Thesource impedence should be matched for the differentialinputs. Poor matching will result in higher even orderharmonics, especially the second.
Figure 2. Equivalent Input Circuit
CSAMPLE7pF
CPARASITIC8pF
CPARASITIC8pF
VDD
LTC1744
AIN+
1744 F02
CSAMPLE7pF
BIAS
VDD
5V
AIN–
ENC
ENC
2V
6k
2V
6k
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14
LTC1744
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APPLICATIO S I FOR ATIO
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Input Drive Circuits
Figure 3 shows the LTC1744 being driven by an RFtransformer with a center tapped secondary. The second-ary center tap is DC biased with VCM, setting the ADC inputsignal at its optimum DC level. Figure 3 shows a 1:1 turnsratio transformer. Other turns ratios can be used if thesource impedence seen by the ADC does not exceed 100Ωfor each ADC input. A disadvantage of using a transformeris the loss of low frequency response. Most small RFtransformers have poor performance at frequencies be-low 1MHz.
frequencies higher than 40MHz, the capacitors may needto be decreased to prevent excessive signal loss.
Reference Operation
Figure 5 shows the LTC1744 reference circuitry consistingof a 2.5V bandgap reference, a difference amplifier andswitching and control circuit. The internal voltage refer-ence can be configured for two pin selectable input rangesof 2V(±1V differential) or 3.2V(±1.6V differential). Tyingthe SENSE pin to ground selects the 2V range; tying theSENSE pin to VDD selects the 3.2V range.
The 2.5V bandgap reference serves two functions: itsoutput provides a DC bias point for setting the commonmode voltage of any external input circuitry; additionally,the reference is used with a difference amplifier to gener-ate the differential reference levels needed by the internalADC circuitry.
1:1 37Ω0.1µF
ANALOGINPUT
VCM
AIN+
AIN–
100Ω 100Ω 18pF
18pF
18pF
1744 F03
4.7µF
37Ω
LTC1744
37Ω
5V
SINGLE-ENDEDINPUT
2.5V ±1/2 RANGE
VCM
AIN+
AIN–
18pF
18pF
18pF
1744 F04a
4.7µF
37Ω
100Ω
500Ω 500Ω
LTC1744
–
+1/2 LT1810
–
+1/2 LT1810
Figure 3. Single-Ended to DifferentialConversion Using a Transformer
Figure 4a. Differential Drive with Op Amps
Figure 4b. Using the LT6600 as a Differential Driver
5V
14
3
GAIN = 402Ω/RINMAXIMUM GAIN = 4
56
2
78
VCM
AIN+
AIN–
18pF
1744 F04b
1µF
49.9Ω
49.9Ω
RIN402Ω
RIN402Ω
0.1µF
0.01µF
LTC1744–
+
–+
LT6600-20VOCM
VMIDVIN
Figure 4a demonstrates the use of operational amplifiersto convert a single ended input signal into a differentialinput signal. The advantage of this method is that itprovides low frequency input response; however, thelimited gain bandwidth of most op amps will limit theSFDR at high input frequencies.
Figure 4b shows the LT6600, a low noise differentialamplifier and lowpass filter, used as an input driver. TheLT6600 provides two functions: it serves as a 4th orderlowpass filter and as a single-ended to differential con-verter. Additionally it can be programmed with one exter-nal resistor to provide a gain from 1 to 4. Three versionsof this device are available having lowpass filter band-widths of 2.5MHz, 10MHz or 20MHz.
The 37Ω resistors and 18pF capacitors on the analoginputs serve two purposes: isolating the drive circuitryfrom the sample-and-hold charging glitches and limitingthe wideband noise at the converter input. For input
-
15
LTC1744
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APPLICATIO S I FOR ATIO
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An external bypass capacitor of 4.7µF or larger is requiredfor the 2.5V reference output, VCM. This provides a highfrequency low impedance path to ground for internal andexternal circuitry. This is also the compensation capacitorfor the reference. It will not be stable without this capacitor.
The difference amplifier generates the high and low refer-ence for the ADC. High speed switching circuits areconnected to these outputs and they must be externallybypassed. Each output has two pins: REFHA and REFHBfor the high reference and REFLA and REFLB for the lowreference. The doubled output pins are needed to reducepackage inductance. Bypass capacitors must be con-nected as shown in Figure 5.
VCM
REFHA
REFLB
SENSETIE TO VDD FOR 3.2V RANGE;
TIE TO GND FOR 2V RANGE;RANGE = 2 • VSENSE FOR
1V < VSENSE < 1.6V
2.5V
REFLA
REFHB
4.7µF
4.7µF
INTERNAL ADCHIGH REFERENCE
BUFFER
0.1µF
1744 F05
LTC1744
4Ω
DIFF AMP
1µF
1µF 0.1µF
INTERNAL ADCLOW REFERENCE
2.5V BANDGAPREFERENCE
1.6V 1V
RANGEDETECT
ANDCONTROL
Figure 5. Equivalent Reference Circuit
VCM
SENSE
2.5V
1.1V
4.7µF14k
1µF11k
1744 F06a
LTC1744
VCM
SENSE
2.5V
5V1.25V64
1, 2
4.7µF
1µF0.1µF
1744 F06b
LTC1744LT1790-1.25
Figure 6a. 2.2V Range ADC Figure 6b. 2.5V Range ADC with an External Reference
Other voltage ranges in between the pin selectable rangescan be programmed with two external resistors as shownin Figure 6a. An external reference can be used by applyingits output directly or through a resistor divider to SENSE.It is not recommended to drive the SENSE pin with a logicdevice since the logic threshold is close to ground andVDD. The SENSE pin should be tied high or low as close tothe converter as possible. If the SENSE pin is drivenexternally, it should be bypassed to ground as close to thedevice as possible with a 1µF ceramic capacitor.
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16
LTC1744
1744f
Input Range
The input range can be set based on the application. Foroversampled signal processing in which the input fre-quency is low (10MHz), the 2V range will have the best SFDR perfor-mance but the SNR will degrade by 3.5dB. See the TypicalPerformance Characteristics section.
APPLICATIO S I FOR ATIO
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Figure 7. Transformer Driven ENC/ENC
VDD
LTC1744
1744 F07
BIAS
VDD
5V
ENC
ENCANALOG INPUT
2V BIAS
2V BIAS
1:40.1µF
CLOCKINPUT
50Ω
6k
6k
TO INTERNALADC CIRCUITS
Driving the Encode Inputs
The noise performance of the LTC1744 can depend on theencode signal quality as much as on the analog input. TheENC/ENC inputs are intended to be driven differentially,primarily for noise immunity from common mode noisesources. Each input is biased through a 6k resistor to a 2Vbias. The bias resistors set the DC operating point fortransformer coupled drive circuits and can set the logicthreshold for single-ended drive circuits.
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17
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1744f
APPLICATIO S I FOR ATIO
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Any noise present on the encode signal will result inadditional aperture jitter that will be RMS summed with theinherent ADC aperture jitter.
In applications where jitter is critical (high input frequen-cies) take the following into consideration:
1. Differential drive should be used.
2. Use as large an amplitude as possible; if transformercoupled use a higher turns ratio to increase theamplitude.
3. If the ADC is clocked with a sinusoidal signal, filter theencode signal to reduce wideband noise.
4. Balance the capacitance and series resistance at bothencode inputs so that any coupled noise will appear atboth inputs as common mode noise.
The encode inputs have a common mode range of 1.8V toVDD. Each input may be driven from ground to VDD forsingle-ended drive.
1744 F08a
ENC2V
VTHRESHOLD = 2VENC
0.1µF
LTC1744
1744 F08b
ENC
ENC
130Ω
3.3V
3.3V130Ω
D0
Q0
Q0
MC100LVELT22
LTC1744
83Ω83Ω
Figure 8a. Single-Ended ENC Drive,Not Recommended for Low Jitter Figure 8b. ENC Drive Using a CMOS-to-PECL Translator
Maximum and Minimum Encode Rates
The maximum encode rate for the LTC1744 is 50Msps. Forthe ADC to operate properly the ENCODE signal shouldhave a 50% (±5%) duty cycle. Each half cycle must haveat least 9.5ns for the ADC internal circuitry to have enoughsettling time for proper operation. Achieving a precise50% duty cycle is easy with differential sinusoidal driveusing a transformer or using symmetric differential logicsuch as PECL or LVDS. When using a single-endedENCODE signal asymmetric rise and fall times can resultin duty cycles that are far from 50%.
At sample rates slower than 50Msps the duty cycle canvary from 50% as long as each half cycle is at least 9.5ns.
The lower limit of the LTC1744 sample rate is determinedby droop of the sample-and-hold circuits. The pipelinedarchitecture of this ADC relies on storing analog signals onsmall valued capacitors. Junction leakage will dischargethe capacitors. The specified minimum operating fre-quency for the LTC1744 is 1Msps.
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18
LTC1744
1744f
DIGITAL OUTPUTS
Digital Output Buffers
Figure 9 shows an equivalent circuit for a single outputbuffer. Each buffer is powered by OVDD and OGND, iso-lated from the ADC power and ground. The additionalN-channel transistor in the output driver allows operationdown to low voltages. The internal resistor in series withthe output makes the output appear as 50Ω to externalcircuitry and may eliminate the need for external dampingresistors.
Output Loading
As with all high speed/high resolution converters thedigital output loading can affect the performance. Thedigital outputs of the LTC1744 should drive a minimalcapacitive load to avoid possible interaction between thedigital outputs and sensitive input circuitry. The outputshould be buffered with a device such as an ALVCH16373CMOS latch. For full speed operation the capacitive loadshould be kept under 10pF. A resistor in series with theoutput may be used but is not required since the ADC hasa series resistor of 43Ω on chip.
Lower OVDD voltages will also help reduce interferencefrom the digital outputs.
Format
The LTC1744 parallel digital output can be selected foroffset binary or 2’s complement format. The format isselected with the MSBINV pin; high selects offset binary.
Overflow Bit
An overflow output bit indicates when the converter isoverranged or underranged. When OF outputs a logic highthe converter is either overranged or underranged.
Output Clock
The ADC has a delayed version of the ENC input availableas a digital output, CLKOUT. The CLKOUT pin can be usedto synchronize the converter data to the digital system.This is necessary when using a sinusoidal ENCODE. Datawill be updated just after CLKOUT falls and can be latchedon the rising edge of CLKOUT.
APPLICATIO S I FOR ATIO
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LTC1744
1744 F09
OVDD
VDD VDD0.1µF
43Ω TYPICALDATAOUTPUT
OGND
OVDD 0.5V TOVDD
PREDRIVERLOGIC
DATAFROM
LATCH
OE
Figure 9. Equivalent Circuit for a Digital Output Buffer
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19
LTC1744
1744f
Output Driver Power
Separate output power and ground pins allow the outputdrivers to be isolated from the analog circuitry. The powersupply for the digital output buffers, OVDD, should be tiedto the same power supply as for the logic being driven. Forexample if the converter is driving a DSP powered by a 3Vsupply then OVDD should be tied to that same 3V supply.OVDD can be powered with any voltage up to 5V. The logicoutputs will swing between OGND and OVDD.
Output Enable
The outputs may be disabled with the output enable pin,OE. OE low disables all data outputs including OF andCLKOUT. The data access and bus relinquish times are tooslow to allow the outputs to be enabled and disabledduring full speed operation. The output Hi-Z state isintended for use during long periods of inactivity.
GROUNDING AND BYPASSING
The LTC1744 requires a printed circuit board with a cleanunbroken ground plane. A multilayer board with an inter-nal ground plane is recommended. The pinout of theLTC1744 has been optimized for a flowthrough layout sothat the interaction between inputs and digital outputs isminimized. Layout for the printed circuit board shouldensure that digital and analog signal lines are separated asmuch as possible. In particular, care should be taken notto run any digital track alongside an analog signal track, anencode signal track or underneath the ADC.
High quality ceramic bypass capacitors should be used atthe VDD, VCM, REFHA, REFHB, REFLA and REFLB pins asshown in the block diagram on the front page of this datasheet. Bypass capacitors must be located as close to thepins as possible. Of particular importance are the capaci-tors between REFHA and REFLB and between REFHB andREFLA. These capacitors should be as close to the deviceas possible (1.5mm or less). Size 0402 ceramic capacitors
are recomended. The large 4.7µF capacitor between REFHAand REFLA can be somewhat further away. The tracesconnecting the pins and bypass capacitors must be keptshort and should be made as wide as possible.
The LTC1744 differential inputs should run parallel andclose to each other. The input traces should be as short aspossible to minimize capacitance and to minimize noisepickup.
An analog ground plane separate from the digital process-ing system ground should be used. All ADC ground pinslabeled GND should connect to this plane. All ADC VDDbypass capacitors, reference bypass capacitors and inputfilter capacitors should connect to this analog plane. TheLTC1744 has three output driver ground pins, labeledOGND (Pins 27, 38 and 47). These grounds should con-nect to the digital processing system ground. The outputdriver supply, OVDD should be connected to the digitalprocessing system supply. OVDD bypass capacitors shouldbypass to the digital system ground. The digital process-ing system ground should connected to the analog planeat ADC OGND (Pin 38).
HEAT TRANSFER
Most of the heat generated by the LTC1744 is transferredfrom the die through the package leads onto the printedcircuit board. In particular, ground pins 12, 13, 36 and 37are fused to the die attach pad. These pins have the lowestthermal resistance between the die and the outside envi-ronment. It is critical that all ground pins are connected toa ground plane of sufficient area. The layout of the evalu-ation circuit shown on the following pages has a low ther-mal resistance path to the internal ground plane by usingmultiple vias near the ground pins. A ground plane of thissize results in a thermal resistance from the die to ambientof 35°C/W. Smaller area ground planes or poorly connectedground pins will result in higher thermal resistance.
APPLICATIO S I FOR ATIO
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DC3
45B
Eval
uatio
n Ci
rcui
t Sch
emat
ic o
f the
LTC
1744
APPLICATIO S I FOR ATIO
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R N1A
33Ω
R633
.2Ω
C4 4.7µ
FC3
10µF
R5 1Ω3 4
1 2
5VU3
LT15
21-3
R N5A
33Ω
R N5B
33Ω
R N5C
33Ω
R N5D
33Ω
R N6A
33Ω
R N6B
33Ω
R N6C
33Ω
R N6D
33Ω
R N7A
33Ω
R N7B
33Ω
R N7C
33Ω
R N7D
33Ω
R N8A
33Ω
R N8B
33Ω
R N1B
33Ω
R N1C
33Ω
R N2A
33Ω
R N2B
33Ω
R N2C
33Ω
R N2D
33Ω
R N3A
33Ω
R N3B
33Ω
R N3C
33Ω
R N3D
33Ω
R N4A
33Ω
R N4B
33Ω
R N4C
33Ω
R N4D
33Ω
C12
0.1µ
F
C10
0.1µ
F
OF
OGND D1
3
D12
D11
OVDD D1
0 D9 D8 D7
OGND GN
D
GND D6 D5 D4
OVDD D3 D2 D1 D0
OGND
CLKO
UT OE
SENS
E
V CM
GND
A IN+
A IN–
GND
V DD
V DD
GND
REFL
B
REFH
A
GND
GND
REFL
A
REFH
B
GND
V DD
V DD
GND
V DD
GND
MSB
INV
ENC
ENC
48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
2OE
2Q8
2Q7
GND
2Q6
2Q5
V CC
2Q4
2Q3
GND
2Q2
2Q1
1Q8
1Q7
GND
1Q6
1Q5
V CC
1Q4
1Q3
GND
1Q2
1Q1
1OE
2LE
2D8
2D7
GND
2D6
2D5
V CC
2D4
2D3
GND
2D2
2D1
1D8
1D7
GND
1D6
1D5
V CC
1D4
1D3
GND
1D2
1D1
1LE
24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
U4P1
74VC
X163
73V
U5LT
C174
4
C19
0.1µ
FC2
00.
1µF
C21
0.1µ
FC2
20.
1µF
1744
TA0
1
C28
0.1µ
F
J232
01S-
40G1
3VU2
10T7
4ALV
C1G8
6JP
2
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
IN TAB
OUT
GND
U1LT
1460
-2.5
V DD
V OUT
C17
4.7µ
FC1
610
µF
E1 5V E2PG
ND
3V
C23
0.1µ
FJP
4JP
3
5V
INPU
TRA
NGE
SELE
CT
TWO
COM
PLEM
ENT
SELE
CT
R Y*
C24*
*18
pF
C25*
*18
pF
C2 4.7µ
FC1
4.7µ
F
5V 5V
*RX,
RY
= IN
PUT
RANG
E SE
T**
DO N
OT IN
STAL
L C2
4, C
25, R
1, R
9 AN
D R1
0
J1ANA
LOG
INPU
T
ENCO
DEIN
PUT
J3 J4
C5 18pF
C29
TBD
R
1**
0Ω
R
10**
0Ω R
9**
10Ω
R8 0Ω
R2 37Ω
T1M
INIC
IRCU
ITS
T1-1
T
R4 100Ω
R3 100Ω
••
R11
50Ω
R22
100Ω
T2M
INIC
IRCU
ITS
T1-1
T
••
R24
2k
R23
3k
R21
100Ω
R7 37Ω
J5
C6 2.2µ
F
C13
0.15
µF
C18
4.7µ
F
C26
0.15
µF
C70.
15µF
C84.
7µF
C9 0.15
µF
C27
0.15
µFC1
50.
15µF
R X*
C14
0.15
µF
C11
1µF
E3 GND
E4 GND
E5 GND
GND
-
21
LTC1744
1744f
Topside Silkscreen
Topside Copper Layer
APPLICATIO S I FOR ATIO
WU UUGround Plane, Layer 2
-
22
LTC1744
1744f
Split Power Plane, Layer 3
Bottom Side Copper, Layer 4
APPLICATIO S I FOR ATIO
WU UU
-
23
LTC1744
1744f
FW Package48-Lead Plastic TSSOP (6.1mm)(Reference LTC DWG # 05-08-1651)
PACKAGE DESCRIPTIO
U
FW48 TSSOP 05020.09 – 0.20(.0035 – .008)
0° – 8°
0.45 – 0.75(.018 – .029)
0.17 – 0.27(.0067 – .0106)
0.50(.0197)
BSC
6.0 – 6.2**(.236 – .244)
7.9 – 8.3(.311 – .327)
1 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
12.4 – 12.6*(.488 – .496)
1.20(.0473)
MAX
0.05 – 0.15(.002 – .006)
2
48 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 2547
C.10-T--C-
MILLIMETERS(INCHES)
DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .152mm (.006") PER SIDEDIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE
NOTE:1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN
3. DRAWING NOT TO SCALE*
**
0.32 ±0.05 0.50 TYP
6.2 ±0.108.1 ±0.10
RECOMMENDED SOLDER PAD LAYOUT
0.95 ±0.10
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
-
24
LTC1744
1744f
LINEAR TECHNOLOGY CORPORATION 2002
LT/TP 0803 1K • PRINTED IN THE USA
PART NUMBER DESCRIPTION COMMENTS
LT®1019 Precision Bandgap Reference 0.05% Max Initial Accuracy, 5ppm/°C Max DriftLTC1196 8-Bit, 1Msps ADC 3V to 5V, SO-8
LTC1405 12-Bit, 5Msps, Sampling ADC with Parallel Output Pin Compatible with the LTC1420
LTC1406 8-Bit, 20Msps ADC Undersampling Capability Up to 70MHz Input
LTC1411 14-Bit, 2.5Msps ADC No Pipeline Delay, 5V, 80dB SINAD
LTC1410 12-Bit, 1.25Msps ADC ±5V, 71dB SINADLTC1412 12-Bit, 3Msps, Sampling ADC with Parallel Output ±5V, No Pipeline Delay, SINAD = 72dB at NyquistLTC1414 14-Bit, 2.2Msps ADC ±5V, No Pipeline Delay, 80dB SINAD, 95dB SFDRLTC1415 Single 5V, 12-Bit, 1.25Msps with Parallel Output 55mW Power Dissipation, 72dB SINAD
LTC1419 14-Bit, 800ksps ADC ±5V, 95dB SFDR, 150mWLTC1420 12-Bit, 10Msps ADC 71dB SINAD and 83dB SFDR at Nyquist
LT1460 Micropower Precision Series Reference 0.075% Accuracy, 10ppm/°C DriftLTC1604/LTC1608 16-Bit, 333ksps/500ksps ADCs 16-Bit, No Missing Codes, 90dB SINAD, –100dB THD
LTC1668 16-Bit, 50Msps DAC 87dB SFDR at 1MHz fOUT, Low Power, Low Cost
LTC1741 12-Bit, 65Msps Low Noise ADC Pin Compatible with the LTC1744
LTC1742 14-Bit, 65Msps Low Noise ADC Pin Compatible with the LTC1744
LTC1743 12-Bit, 50Msps Low Noise ADC Pin Compatible with the LTC1744
LTC1745 12-Bit, 25Msps Low Noise ADC Pin Compatible with the LTC1744
LTC1746 14-Bit, 25Msps Low Noise ADC Pin Compatible with the LTC1744
LTC1747 12-Bit, 80Msps Low Noise ADC Pin Compatible with the LTC1744
LTC1748 14-Bit, 80Msps Low Noise ADC Pin Compatible with the LTC1744
RELATED PARTS
Linear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com