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LTC1748 14-Bit, 80Msps Low Noise ADC
FEATURES
s s s s s s s s s
DESCRIPTIO
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Sample Rate: 80Msps 76.3dB SNR and 90dB SFDR (3.2V Range) 72.6dB SNR and 90dB SFDR (2V Range) No Missing Codes Single 5V Supply Power Dissipation: 1.4W Selectable Input Ranges: 1V or 1.6V 240MHz 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
The LTC (R)1748 is an 80Msps, sampling 14-bit A/D converter designed for digitizing high frequency, wide dynamic range signals. Pin selectable input ranges of 1V and 1.6V along with a resistor programmable mode allow the LTC1748's input range to be optimized for a wide variety of applications. The LTC1748 is perfect for demanding communications applications with AC performance that includes 76.3dB SNR and 90dB spurious free dynamic range. Ultralow jitter of 0.15psRMS allows undersampling of IF frequencies with excellent noise performance. DC specs include 3LSB INL and no missing codes. The digital interface is compatible with 5V, 3V, 2V and LVDS logic systems. The ENC and ENC inputs may be driven differentially from PECL, GTL and other low swing logic families or from single-ended TTL or CMOS. The low noise, high gain ENC and ENC inputs may also be driven by a sinusoidal signal without degrading performance. A separate output power supply can be operated from 0.5V to 5V, making it easy to connect directly to any low voltage DSPs or FIFOs. The TSSOP package with a flow-through pinout simplifies the board layout.
APPLICATIO S
s s s s s
Telecommunications Receivers Cellular Base Stations Spectrum Analysis Imaging Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
BLOCK DIAGRA
AIN+ 1V DIFFERENTIAL ANALOG INPUT
80Msps, 14-Bit ADC with a 2V Differential Input Range
OVDD 0.1F OF D13 D0 CLKOUT 0.5V TO 5V 0.1F CORRECTION LOGIC AND SHIFT REGISTER 14
AIN-
S/H AMP
14-BIT PIPELINED ADC
SENSE BUFFER RANGE SELECT
DIFF AMP 1F GND CONTROL LOGIC
1748 BD
VCM 4.7F
2.35VREF
REFLB 0.1F 1F
REFHA 4.7F
REFLA
REFHB ENC
ENC
0.1F 1F
DIFFERENTIAL ENCODE INPUT
U
OUTPUT LATCHES * * * OGND VDD 1F 5V 1F MSBINV OE
W
U
1748fa
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LTC1748
ABSOLUTE MAXIMUM RATINGS
OVDD = VDD (Notes 1, 2)
PACKAGE/ORDER INFORMATION
TOP VIEW SENSE VCM GND AIN+ AIN- GND VDD VDD GND REFLB REFHA GND GND REFLA REFHB GND VDD VDD GND VDD GND MSBINV ENC ENC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 FW PACKAGE 48-LEAD PLASTIC TSSOP 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 OF OGND D13 D12 D11 OVDD D10 D9 D8 D7 OGND GND GND D6 D5 D4 OVDD D3 D2 D1 D0 OGND CLKOUT OE
Supply Voltage (VDD) ............................................. 5.5V Analog 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 1V Power Dissipation ............................................ 2000mW Operating Temperature Range LTC1748C ............................................... 0C to 70C LTC1748I ............................................ - 40C to 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LTC1748CFW LTC1748IFW
TJMAX = 150C, JA = 35C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
CO VERTER CHARACTERISTICS
PARAMETER Resolution (No Missing Codes) Integral Linearity Error Differential Linearity Error Offset Error Gain Error Full-Scale Tempco Offset Tempco Input Referred Noise (Transition Noise)
The q indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5)
CONDITIONS
q
(Note 6)
q
(Note 7) External Reference (SENSE = 1.6V) Internal Reference External Reference (SENSE = 1.6V) SENSE = 1.6V
MIN 14 -3 -1 - 35 - 3.5
TYP 0.75 0.5 8 1 40 20 20 0.82
MAX 3 1.5 35 3.5
UNITS Bits LSB LSB mV %FS ppm/C ppm/C V/C LSBRMS
A ALOG I PUT
SYMBOL VIN IIN CIN tACQ tAP tJITTER CMRR
The q indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5)
PARAMETER Analog Input Range (Note 8) Analog Input Leakage Current Analog Input Capacitance Sample-and-Hold Acquisition Time Sample-and-Hold Acquisition Delay Time Sample-and-Hold Acquisition Delay Time Jitter Analog Input Common Mode Rejection Ratio CONDITIONS 4.75V VDD 5.25V 0 < AIN+, AIN- < VDD Sample Mode ENC < ENC Hold Mode ENC > ENC MIN
q q
TYP 1 to 1.6 8 4 5 0 0.15 80
MAX 1
-1
q
6
1.5V < (AIN- = AIN+) < 3V
UNITS V A pF pF ns ns psRMS dB
1748fa
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WW
W
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LTC1748
DY A IC ACCURACY
SYMBOL SNR PARAMETER Signal-to-Noise Ratio
SFDR
S/(N + D)
THD
IMD
I TER AL REFERE CE CHARACTERISTICS
PARAMETER VCM Output Voltage VCM Output Tempco VCM Line Regulation VCM Output Resistance CONDITIONS IOUT = 0 IOUT = 0 4.75V VDD 5.25V 1mA IOUT 1mA
U
WU U
TA = 25C, AIN = -1dBFS (Note 5)
CONDITIONS 5MHz Input Signal (2V Range) 5MHz Input Signal (3.2V Range) 30MHz Input Signal (2V Range) 30MHz Input Signal (3.2V Range) 70MHz Input Signal (2V Range) 70MHz Input Signal (3.2V Range) 140MHz Input Signal (2V Range) 250MHz Input Signal (2V Range) MIN 75 74 TYP 72.6 76.3 72.5 76.1 72.2 75.4 71.4 68.9 90 90 94 90 80 85 88 94 85 76 94 77 93 64 89 74.5 72.4 76.0 72.3 75.6 71 71 -90 -90 -90 -85 -78 -74 97 93 240 MAX UNITS dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dB dBc dBc MHz
Spurious Free Dynamic Range
5MHz Input Signal (2V Range) 5MHz Input Signal (3.2V Range) (2nd and 3rd) 5MHz Input Signal (3.2V Range) (Other) 30MHz Input Signal (2V Range) 30MHz Input Signal (3.2V Range) (2nd and 3rd) 30MHz Input Signal (3.2V Range) (Other) 70MHz Input Signal (2V Range) 70MHz Input Signal (3.2V Range) (2nd and 3rd) 70MHz Input Signal (3.2V Range) (Other) 140MHz Input Signal (2VRange) (2nd and 3rd) 140MHz Input Signal (2V Range) (Other) 250MHz Input Signal (2V Range) (2nd and 3rd) 250MHz Input Signal (2V Range) (Other)
Signal-to-(Noise + Distortion) Ratio
5MHz Input Signal (2V Range) 5MHz Input Signal (3.2V Range) 30MHz Input Signal (2V Range) 30MHz Input Signal (3.2V Range) 70MHz Input Signal (2V Range) 70MHz Input Signal (3.2V Range)
Total Harmonic Distortion
5MHz Input Signal, First 5 Harmonics (2V Range) 5MHz Input Signal, First 5 Harmonics (3.2V Range) 30MHz Input Signal, First 5 Harmonics (2V Range) 30MHz Input Signal, First 5 Harmonics (3.2V Range) 70MHz Input Signal, First 5 Harmonics (2V Range) 70MHz Input Signal, First 5 Harmonics (3.2V Range)
Intermodulation Distortion Sample-and-Hold Bandwidth
fIN1 = 2.52MHz, fIN2 = 5.2MHz (2V Range) fIN1 = 2.52MHz, fIN2 = 5.2MHz (3.2V Range) RSOURCE = 50
U
(Note 5)
MIN 2.30 TYP 2.35 30 3 4 MAX 2.40 UNITS V ppm/C mV/V
1748fa
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LTC1748 DIGITAL I PUTS A D DIGITAL OUTPUTS
SYMBOL VIH VIL IIN CIN VOH VOL IOZ COZ ISOURCE ISINK PARAMETER High Level Input Voltage Low Level Input Voltage Digital Input Current Digital Input Capacitance High Level Output Voltage Low Level Output Voltage Hi-Z Output Leakage D13 to D0 Hi-Z Output Capacitance D13 to D0 Output Source Current Output Sink Current CONDITIONS VDD = 5.25V, MSBINV and OE VDD = 4.75V, MSBINV and OE VIN = 0V to VDD MSBINV and OE Only OVDD = 4.75V OVDD = 4.75V VOUT = 0V to VDD, OE = High OE = High (Note 8) VOUT = 0V VOUT = 5V IO = -10A IO = - 200A IO = 160A IO = 1.6mA
q q q q q q q
The q indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5)
MIN 2.4 0.8 10 1.5 4.74 4 4.74 0.05 0.1 0.4 10 15 - 50 50 TYP MAX UNITS V V A pF V V V V A pF mA mA
POWER REQUIRE E TS
SYMBOL VDD IDD PDIS OVDD PARAMETER Positive Supply Voltage Positive Supply Current Power Dissipation Digital Output Supply Voltage
The q indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5)
CONDITIONS q q 0.5 MIN 4.75 280 1.4 TYP MAX 5.25 310 1.55 VDD UNITS V mA W V
TI I G CHARACTERISTICS
SYMBOL t0 t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 t12 PARAMETER ENC Period ENC High ENC Low Aperture Delay ENC to CLKOUT Falling ENC to CLKOUT Rising For 80Msps 50% Duty Cycle ENC to DATA Delay ENC to DATA Delay (Hold Time) ENC to DATA Delay (Setup Time) For 80Msps 50% Duty Cycle CLKOUT to DATA Delay (Hold Time), 80Msps 50% Duty Cycle CLKOUT to DATA Delay (Setup Time), 80Msps 50% Duty Cycle DATA Access Time After OE BUS Relinquish Data Latency
The q indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. (Note 5)
CONDITIONS (Note 9) (Note 8) (Note 8) (Note 8) CL = 10pF (Note 8) CL = 10pF (Note 8) CL = 10pF (Note 8) CL = 10pF (Note 8) (Note 8) CL = 10pF (Note 8) CL = 10pF (Note 8) (Note 8) CL = 10pF (Note 8) CL = 10pF (Note 8) (Note 8) q q q 5.3 6 2.1 10 10 5 25 25 q q q 7.25 2 1.4 q 1 q q q MIN 12.5 6 6 0 2.4 t1 + t 4 8.65 4.9 3.4 t0 - t 6 7.6 10.5 10.25 7.2 4.7 4 TYP MAX 2000 1000 1000 UNITS ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns cycles
1748fa
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LTC1748
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: All voltage values are with respect to GND (unless otherwise noted). Note 3: When these pin voltages are taken below GND or above VDD, they will be clamped by internal diodes. This product can handle input currents of greater than 100mA below GND or above VDD without latchup. Note 4: When these pin voltages are taken below GND, they will be clamped 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 = 80MHz, differential ENC/ENC = 2VP-P 80MHz sine wave, input range = 1.6V differential, unless otherwise specified. Note 6: Integral nonlinearity is defined as the deviation of a code from a straight 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 LSB when the output code flickers between 00 0000 0000 0000 and 11 1111 1111 1111. Note 8: Guaranteed by design, not subject to test. Note 9: Recommended operating conditions.
TYPICAL PERFOR A CE CHARACTERISTICS
INL, 3.2V Range
2.5 2.0 1.5 1.0 TA = 25C 1.0 0.8 0.6
AMPLITUDE (dBFS)
ERROR (LSB)
0.5 0 -0.5 -1.0 -1.5 -2.0 -2.5 0 4096 8192 12288 OUTPUT CODE 16384
1748 G01
ERROR (LSB)
8192 Point FFT, Input Frequency = 15.068MHz, -10dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
-50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
AMPLITUDE (dBFS)
UW
1748 G04
DNL, 3.2V Range
TA = 25C
8192 Point FFT, Input Frequency = 15.068MHz, -1dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120
0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 0 4096 12288 8192 OUTPUT CODE 16384
1748 G02
0
5
10
15 20 25 30 FREQUENCY (MHz)
35
40
1748 G03
8192 Point FFT, Input Frequency = 15.068MHz, -20dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40
8192 Point FFT, Input Frequency = 30.068MHz, -1dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
1748 G05
1748 G06
1748fa
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LTC1748 TYPICAL PERFOR A CE CHARACTERISTICS
8192 Point FFT, Input Frequency = 30.068MHz, -10dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
-50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
AMPLITUDE (dBFS)
8192 Point FFT, Input Frequency = 40.64MHz, -10dB, 3.2V Range
0 TA = 25C -10 -20
AMPLITUDE (dBFS) AMPLITUDE (dBFS)
-50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
-50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
AMPLITUDE (dBFS)
-30 -40
8192 Point FFT, Input Frequency = 50.64MHz, -10dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
-50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
AMPLITUDE (dBFS)
6
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1748 G07
8192 Point FFT, Input Frequency = 30.068MHz, -20dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40
8192 Point FFT, Input Frequency = 40.64MHz, -1dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
1748 G08
1748 G09
8192 Point FFT, Input Frequency = 40.64MHz, -20dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40
8192 Point FFT, Input Frequency = 50.64MHz, -1dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
1748 G10
1748 G11
1748 G12
8192 Point FFT, Input Frequency = 50.64MHz, -20dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40
8192 Point FFT, Input Frequency = 69.1MHz, -1dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
1748 G13
1748 G14
1748 G15
1748fa
LTC1748 TYPICAL PERFOR A CE CHARACTERISTICS
8192 Point FFT, Input Frequency = 69.1MHz, -10dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
-50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
AMPLITUDE (dBFS)
8192 Point 2-Tone FFT, Input Frequency = 25MHz and 30MHz, -7dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
SFDR dBc AND dBFS
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
SFDR vs 30MHz Input Level
120 110 100 90 80 70 60 50 40 30 20 10 0 -80 -70 -60 -50 -40 -30 -20 -10 INPUT LEVEL (dBFS) 0 dBc TA = 25C dBFS
SFDR dBc AND dBFS
SFDR dBc AND dBFS
70 60 50 40 30 20 10 0 -80 -70 -60 -50 -40 -30 -20 -10 INPUT LEVEL (dBFS) 0 dBc
SFDR dBc AND dBFS
UW
1748 G16 1748 G19
8192 Point FFT, Input Frequency = 69.1MHz, -20dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120
8192 Point 2-Tone FFT, Input Frequency = 5MHz and 7MHz, -7dB, 3.2V Range
TA = 25C
0
5
10
15 20 25 30 FREQUENCY (MHz)
35
40
1748 G17
1748 G18
8192 Point 2-Tone FFT, Input Frequency = 65MHz and 70MHz, -7dB, 3.2V Range
0 TA = 25C -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 0 5 10 15 20 25 30 FREQUENCY (MHz) 35 40
SFDR vs 15MHz Input Level
120 110 100 90 80 70 60 50 40 30 20 10 0 -80 -70 -60 -50 -40 -30 -20 -10 INPUT LEVEL (dBFS) 0 dBc dBFS TA = 25C
1748 G20
1748 G21
SFDR vs 50.3MHz Input Level
120 TA = 25C 110 100 90 80 dBFS
SFDR vs 70.3MHz Input Level
120 TA = 25C 110 100 90 80 70 60 50 40 30 20 10 0 -80 -70 -60 -50 -40 -30 -20 -10 INPUT LEVEL (dBFS) 0 dBc dBFS
1748 G22
1748 G23
1748 G24
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LTC1748 TYPICAL PERFOR A CE CHARACTERISTICS
SFDR vs Input Frequency and Amplitude, 3.2V Range, 2nd and 3rd Harmonic
100 95 90 -6dB SFDR (dBFS) TA = 25C
-20dB -10dB
SFDR (dBFS)
85 80 -1dB 75 70 65 60 0 20 80 60 INPUT FREQUENCY (MHz) 40 100
1748 G25
80 75
COUNT
SNR vs Input Frequency 3.2V Range
78.0 77.5 77.0 SNR (dBFS) TA = 25C 77.0 76.8 76.6
76.2 76.0 75.8 75.6 75.4 15MHz 30MHz 50MHz 70MHz -60 -40 INPUT LEVEL -20 0
1748 G29
76.0 75.5 75.0 74.5 74.0 0 20 80 60 INPUT FREQUENCY (MHz) 40 100
1748 G28
SFDR (dBFS)
SNR (dBFS)
76.5
SNR vs Sample Rate, 5MHz Input, -1dB, 3.2V Range
78 77 76 TA = 25C
100 95 90
SFDR (dBFS)
SNR (dBFS)
SNR (dBFS)
75 74 73 72 0 20 40 60 80 SAMPLE RATE (Msps) 100
1748 G31
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SFDR vs Input Frequency and Amplitude, 2V Range, 2nd and 3rd Harmonic
100 95 90 -6dB 85 -1dB TA = 25C
18000
Shorted Input Histogram
TA = 25C 16000 14000 12000 10000 8000 6000
-20dB -10dB
70 65 60 0 20 80 60 INPUT FREQUENCY (MHz) 40 100
1748 G26
4000 2000 0 8147 8148 8149 8150 8151 8152 8153 CODE
1748 G27
SNR vs Input Level and Frequency 3.2V Range
TA = 25C 100 95 90 85 80 75 70 65 60
SFDR vs Sample Rate, 5MHz Input, -1dB, 3.2V Range
TA = 25C
76.4
75.2 -80
0
20
40 80 60 SAMPLE RATE (Msps)
100
1748 G30
High Input Frequency SFDR, -1dB, 2V Range
73.0
High Input Frequency SNR, -1dB, 2V Range
72.5 72.0 71.5 71.0 70.5 70.0 69.5 69.0
4TH OR HIGHER HARMONIC
85 80 75 2ND OR 3RD HARMONIC 70 65 60 0 50 100 200 150 INPUT FREQUENCY (MHz) 250
1748 G33
68.5 0 200 50 150 100 INPUT FREQUENCY (MHz) 250
1748 G34
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LTC1748 TYPICAL PERFOR A CE CHARACTERISTICS
Offset and Gain Error vs Temperature
8 6 GAIN ERROR 300 290
SUPPLY CURRENT (mA)
4
ERROR (LSB)
2 0 -2 -4 -6 -8 - 50 -30 -10 50 30 10 TEMPERATURE (C) 70 90
1748 G35
PI FU CTIO S
SENSE (Pin 1): Reference Sense Pin. Ground selects 1V. VDD selects 1.6V. Greater than 1V and less than 1.6V applied to the SENSE pin selects an input range of VSENSE, 1.6V is the largest valid input range. VCM (Pin 2): 2.35V Output and Input Common Mode Bias. Bypass to ground with 4.7F ceramic chip capacitor. GND (Pins 3, 6, 9, 12, 13, 16, 19, 21, 36, 37): ADC Power 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 AGND with 1F ceramic chip capacitors at Pin 8 and Pin 18. REFLB (Pin 10): ADC Low Reference. Bypass to Pin 11 with 0.1F ceramic chip capacitor. Do not connect to Pin 14. REFHA (Pin 11): ADC High Reference. Bypass to Pin 10 with 0.1F ceramic chip capacitor, to Pin 14 with a 4.7F ceramic capacitor and to ground with 1F ceramic capacitor. REFLA (Pin 14): ADC Low Reference. Bypass to Pin 15 with 0.1F ceramic chip capacitor, to Pin 11 with a 4.7F ceramic capacitor and to ground with 1F ceramic capacitor. REFHB (Pin 15): ADC High Reference. Bypass to Pin 14 with 0.1F ceramic chip capacitor. Do not connect to Pin 11. MSBINV (Pin 22): MSB Inversion Control. Low inverts the MSB, 2's complement output format. High does not invert the MSB, offset binary output format. ENC (Pin 23): Encode Input. The input sample starts on the positive edge. ENC (Pin 24): Encode Complement Input. Conversion starts on the negative edge. Bypass to ground with 0.1F ceramic for single-ended ENCODE signal. OE (Pin 25): Output Enable. Low enables outputs. Logic high makes outputs Hi-Z. OE should not exceed the votlage on OVDD. CLKOUT (Pin 26): Data Valid Output. Latch data on the rising edge of CLKOUT. OGND (Pins 27, 38, 47): Output Driver Ground. D0-D3 (Pins 28 to 31): Digital Outputs. OVDD (Pins 32, 43): Positive Supply for the Output Drivers. Bypass to ground with 0.1F 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. OF (Pin 48): Over/Under Flow Output. High when an over or under flow has occurred.
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Supply Current vs Sample Rate
TA = 25C
280 270 260 250 240 230 0 20 40 60 80 100
1748 G32
OFFSET ERROR
SAMPLE RATE (Msps)
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LTC1748 TI I G DIAGRA
N ANALOG INPUT t3 t1 ENC t7 DATA t6 CLKOUT t4 t5 OE t11 DATA t12 DATA N DB13 TO DB0, OF AND CLKOUT t10 t9 t8 DATA (N - 5) DB13 TO DB0 DATA (N - 4) DB13 TO DB0 DATA (N - 3) t2 t0
*
APPLICATIO S I FOR ATIO
DYNAMIC PERFORMANCE Signal-to-Noise Plus Distortion Ratio
The signal-to-noise plus distortion ratio [S/(N + D)] is the ratio between the RMS amplitude of the fundamental input frequency and the RMS amplitude of all other frequency components at the ADC output. The output is band limited to frequencies above DC to below half the sampling frequency. Signal-to-Noise Ratio The signal-to-noise ratio (SNR) is the ratio between the RMS amplitude of the fundamental input frequency and the RMS amplitude of all other frequency components except the first five harmonics and DC. Total Harmonic Distortion Total harmonic distortion is the ratio of the RMS sum of all harmonics of the input signal to the fundamental itself. The out-of-band harmonics alias into the frequency band between DC and half the sampling frequency. THD is expressed as:
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1748 TD
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THD = 20Log
V22 + V32 + V 42 + ...Vn2 V1
where V1 is the RMS amplitude of the fundamental frequency and V2 through Vn are the amplitudes of the second through nth harmonics. The THD calculated in this data sheet uses all the harmonics up to the fifth. Intermodulation Distortion If the ADC input signal consists of more than one spectral component, the ADC transfer function nonlinearity can produce intermodulation distortion (IMD) in addition to THD. IMD is the change in one sinusoidal input caused by the presence of another sinusoidal input at a different frequency. If two pure sine waves of frequencies fa and fb are applied to the ADC input, nonlinearities in the ADC transfer function can create distortion products at the sum and difference frequencies of mfa nfb, where m and n = 0, 1, 2, 3, etc. The 3rd order intermodulation products are 2fa + fb, 2fb + fa, 2fa - fb and 2fb - fa. The intermodulation distortion is defined as the ratio of the RMS value of either input tone to the RMS value of the largest 3rd order intermodulation product.
1748fa
LTC1748
APPLICATIO S I FOR ATIO
Spurious Free Dynamic Range (SFDR)
Spurious free dynamic range is the peak harmonic or spurious noise that is the largest spectral component excluding the input signal and DC. This value is expressed in decibels relative to the RMS value of a full scale input signal. Input Bandwidth The input bandwidth is that input frequency at which the amplitude of the reconstructed fundamental is reduced by 3dB for a full scale input signal. Aperture Delay Time The time from when a rising ENC equals the ENC voltage to the instant that the input signal is held by the sample and hold circuit. Aperture Delay Jitter The variation in the aperture delay time from conversion to conversion. This random variation will result in noise
AIN+ AIN- INPUT S/H FIRST PIPELINED ADC STAGE (5 BITS) SECOND PIPELINED ADC STAGE (4 BITS) THIRD PIPELINED ADC STAGE (4 BITS) FOURTH PIPELINED ADC STAGE (4 BITS)
VCM 4.7F
2.35V REFERENCE SHIFT REGISTER AND CORRECTION
RANGE SELECT
REFL SENSE REF BUF
DIFF REF AMP
REFLB REFHA 4.7F 0.1F 1F
Figure 1. Functional Block Diagram
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when sampling an AC input. The signal to noise ratio due to the jitter alone will be: SNRJITTER = -20log (2) * FIN * TJITTER CONVERTER OPERATION The LTC1748 is a CMOS pipelined multistep converter. The converter has four pipelined ADC stages; a sampled analog input will result in a digitized value five cycles later, see the Timing Diagram section. The analog input is differential for improved common mode noise immunity and to maximize the input range. Additionally, the differential input drive will reduce even order harmonics of the sample-and-hold circuit. The encode input is also differential for improved common mode noise immunity. The LTC1748 has two phases of operation, determined by the state of the differential ENC/ENC input pins. For brevity, the text will refer to ENC greater than ENC as ENC high and 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.
REFH INTERNAL CLOCK SIGNALS OVDD 0.5V TO 5V OF D13 CONTROL LOGIC AND CALIBRATION LOGIC OUTPUT DRIVERS DIFFERENTIAL INPUT LOW JITTER CLOCK DRIVER D0 CLKOUT
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REFLA REFHB 0.1F 1F
ENC
ENC
MSBINV
OE
OGND
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LTC1748
APPLICATIO S I FOR ATIO
In operation, the ADC quantizes the input to the stage and the quantized value is subtracted from the input by the DAC to produce a residue. The residue is amplified and output by the residue amplifier. Successive stages operate out of phase so that when the odd stages are outputting their residue, the even stages are acquiring that residue and visa versa. When ENC is low, the analog input is sampled differentially directly onto the input sample-and-hold capacitors, inside the "Input S/H" shown in the block diagram. At the instant that ENC transitions from low to high, the sampled input is held. While ENC is high, the held input voltage is buffered by the S/H amplifier which drives the first pipelined ADC stage. The first stage acquires the output of the S/H during this high phase of ENC. When ENC goes back low, the first stage produces its residue which is acquired by the second stage. At the same time, the input S/H goes back to acquiring the analog input. When ENC goes back high, the second stage produces its residue which is acquired by the third stage. An identical process is repeated for the third stage, resulting in a third stage residue that is sent to the fourth stage ADC for final evaluation. Each ADC stage following the first has additional range to accommodate flash and amplifier offset errors. Results from all of the ADC stages are digitally synchronized such that the results can be properly combined in the correction logic before being sent to the output buffer. SAMPLE/HOLD OPERATION AND INPUT DRIVE Sample/Hold Operation Figure 2 shows an equivalent circuit for the LTC1748 CMOS differential sample-and-hold. The differential analog inputs are sampled directly onto sampling capacitors (CSAMPLE) through CMOS transmission gates. This direct capacitor sampling results in lowest possible noise for a given sampling capacitor size. The capacitors shown attached to each input (CPARASITIC) are the summation of all other capacitance associated with each input. During the sample phase when ENC/ENC is low, the transmission gate connects the analog inputs to the sampling capacitors and they charge to, and track the differential input voltage. When ENC/ENC transitions from low to
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LTC1748 VDD CSAMPLE 4pF CPARASITIC 4pF CSAMPLE 4pF CPARASITIC 4pF 5V AIN+ VDD AIN- BIAS 2V 6k ENC ENC 6k 2V
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Figure 2. Equivalent Input Circuit
high the sampled input voltage is held on the sampling capacitors. During the hold phase when ENC/ENC is high the sampling capacitors are disconnected from the input and the held voltage is passed to the ADC core for processing. As ENC/ENC transitions from high to low the inputs are reconnected to the sampling capacitors to acquire a new sample. Since the sampling capacitors still hold the previous sample, a charging glitch proportional to the change in voltage between samples will be seen at this time. If the change between the last sample and the new sample is small the charging glitch seen at the input will be small. If the input change is large, such as the change seen with input frequencies near Nyquist, then a larger charging glitch will be seen. Common Mode Bias The ADC sample-and-hold circuit requires differential drive to achieve specified performance. Each input should swing 0.8V for the 3.2V range or 0.5V for the 2V range, around a common mode voltage of 2.35V. The VCM output pin (Pin 2) may be used to provide the common mode bias level. VCM can be tied directly to the center tap of a transformer to set the DC input level or as a reference level to an op amp differential driver circuit. The VCM pin must be bypassed to ground close to the ADC with a 4.7F or greater capacitor.
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LTC1748
APPLICATIO S I FOR ATIO
Input Drive Impedance
As with all high performance, high speed ADCs the dynamic performance of the LTC1748 can be influenced by the input drive circuitry, particularly the second and third harmonics. Source impedance and input reactance can influence SFDR. At the falling edge of encode the sampleand-hold circuit will connect the 4pF sampling capacitor to the input pin and start the sampling period. The sampling period ends when encode rises, holding the sampled input on the sampling capacitor. Ideally the input circuitry should be fast enough to fully charge the sampling capacitor during the sampling period 1/(2FENCODE); however, this is not always possible and the incomplete settling may degrade the SFDR. The sampling glitch has been designed to be as linear as possible to minimize the effects of incomplete settling. For the best performance, it is recomended to have a source impedence of 100 or less for each input. The S/H circuit is optimized for a 50 source impedance. If the source impedance is less than 50, a series resistor should be added to increase this impedance to 50. The source impedence should be matched for the differential inputs. Poor matching will result in higher even order harmonics, especially the second. Input Drive Circuits Figure 3 shows the LTC1748 being driven by an RF transformer with a center tapped secondary. The secondary center tap is DC biased with VCM, setting the ADC input signal at its optimum DC level. Figure 3 shows a 1:1 turns ratio transformer. Other turns ratios can be used if the
VCM 4.7F
0.1F ANALOG INPUT 100 1:1
25 100 25
12pF
25 AIN+ 25 AIN-
12pF
12pF
Figure 3. Single-Ended to Differential Conversion Using a Transformer
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source impedence seen by the ADC does not exceed 100 for each ADC input. A disadvantage of using a transformer is the loss of low frequency response. Most small RF transformers have poor performance at frequencies below 1MHz. Figure 4 demonstrates the use of operational amplifiers to convert a single ended input signal into a differential input signal. The advantage of this method is that it provides low frequency input response; however, the limited gain bandwidth of most op amps will limit the SFDR at high input frequencies. The 25 resistors and 12pF capacitors on the analog inputs serve two purposes: isolating the drive circuitry from the sample-and-hold charging glitches and limiting the wideband noise at the converter input. For input frequencies higher than 100MHz, the capacitors may need to be decreased to prevent excessive signal loss. Reference Operation Figure 5 shows the LTC1748 reference circuitry consisting of a 2.35V bandgap reference, a difference amplifier and switching and control circuit. The internal voltage reference can be configured for two pin selectable input ranges of 2V(1V differential) or 3.2V(1.6V differential). Tying the SENSE pin to ground selects the 2V range; tying the SENSE pin to VDD selects the 3.2V range. The 2.35V bandgap reference serves two functions: its output provides a DC bias point for setting the common
VCM 4.7F 5V SINGLE-ENDED INPUT 2.35V 1/2 RANGE 12pF 25 25 AIN+ LTC1748 12pF
LTC1748
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+
1/2 LT1810
-
100
+
1/2 LT1810
25
25 AIN- 12pF
-
500
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500
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Figure 4. Differential Drive with Op Amps
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LTC1748
APPLICATIO S I FOR ATIO
mode voltage of any external input circuitry; additionally, the reference is used with a difference amplifier to generate the differential reference levels needed by the internal ADC circuitry. An external bypass capacitor is required for the 2.35V reference output, VCM. This provides a high frequency low impedance path to ground for internal and external circuitry. This is also the compensation capacitor for the reference. It will not be stable without this capacitor. The difference amplifier generates the high and low reference for the ADC. High speed switching circuits are connected to these outputs and they must be externally bypassed. Each output has two pins: REFHA and REFHB for the high reference and REFLA and REFLB for the low reference. The doubled output pins are needed to reduce package inductance. Bypass capacitors must be connected as shown in Figure 5. Other voltage ranges in between the pin selectable ranges can be programmed with two external resistors as shown in Figure 6a. An external reference can be used by applying its output directly or through a resistor divider to SENSE. It is not recommended to drive the SENSE pin with a logic device since the logic threshold is close to ground and
LTC1748 2.35V VCM 4.7F 1.6V RANGE DETECT AND CONTROL SENSE 1V 4 2.35V BANDGAP REFERENCE
TIE TO VDD FOR 3.2V RANGE; TIE TO GND FOR 2V RANGE; RANGE = 2 * VSENSE FOR 1V < VSENSE < 1.6V 1F
REFLB 0.1F REFHA
BUFFER INTERNAL ADC HIGH REFERENCE
4.7F DIFF AMP 1F REFLA 0.1F REFHB INTERNAL ADC LOW REFERENCE
1748 F05
Figure 5. Equivalent Reference Circuit
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VDD. The SENSE pin should be tied high or low as close to the converter as possible. If the SENSE pin is driven externally, it should be bypassed to ground as close to the device as possible with a 1F ceramic capacitor. Input Range The input range can be set based on the application. For oversampled signal processing in which the input frequency is low (<10MHz), the largest input range will provide the best signal-to-noise performance while maintaining excellent SFDR. For high input frequencies (> 40MHz), the 2V range will have the best SFDR performance for the 2nd and 3rd harmonics, but the SNR will degrade by 3.5dB. See the Typical Performance Characteristics section. Driving the Encode Inputs The noise performance of the LTC1748 can depend on the encode signal quality as much as on the analog input. The ENC/ENC inputs are intended to be driven differentially, primarily for noise immunity from common mode noise sources. Each input is biased through a 6k resistor to a 2V bias. The bias resistors set the DC operating point for transformer coupled drive circuits and can set the logic threshold for single-ended drive circuits.
2.35V VCM 4.7F 12.5k 1.1V 11k SENSE 1F LTC1748
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Figure 6a. 2.2V Range ADC
VCM 4.7F 4 6 1.25V SENSE 1F LTC1748
2.35V
5V 0.1F
LT1790-1.25 1, 2
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Figure 6b. 2.5V Range ADC with External Reference
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LTC1748
APPLICATIO S I FOR ATIO
ANALOG INPUT 0.1F CLOCK INPUT 50 1:4
ENC
ENC
Figure 7. Transformer Driven ENC/ENC
3.3V MC100LVELT22 3.3V 130 Q0 130 ENC LTC1748
VTHRESHOLD = 2V
ENC
D0
2V ENC 0.1F
LTC1748
Q0 83
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Figure 8a. Single-Ended ENC Drive, Not Recommended for Low Jitter
Any noise present on the encode signal will result in additional aperture jitter that will be RMS summed with the inherent ADC aperture jitter. In applications where jitter is critical (high input frequencies) take the following into consideration: 1. Differential drive should be used. 2. Use as large an amplitude as possible; if transformer coupled use a higher turns ratio to increase the amplitude. 3. If the ADC is clocked with a sinusoidal signal, filter the encode signal to reduce wideband noise. 4. Balance the capacitance and series resistance at both encode inputs so that any coupled noise will appear at both inputs as common mode noise.
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LTC1748 5V BIAS 2V BIAS 6k TO INTERNAL ADC CIRCUITS VDD VDD 2V BIAS 6k
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ENC 83
Figure 8b. ENC Drive Using a CMOS-to-PECL Translator
The encode inputs have a common mode range of 1.8V to VDD. Each input may be driven from ground to VDD for single-ended drive. Maximum and Minimum Encode Rates The maximum encode rate for the LTC1748 is 80Msps. For the ADC to operate properly the encode signal should have a 50% (4%) duty cycle. Each half cycle must have at least 6ns for the ADC internal circuitry to have enough settling time for proper operation. Achieving a precise 50% duty cycle is easy with differential sinusoidal drive using a transformer or using symmetric differential logic such as PECL or LVDS. When using a single-ended encode signal asymmetric rise and fall times can result in duty cycles that are far from 50%.
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LTC1748
APPLICATIO S I FOR ATIO
At sample rates slower than 80Msps the duty cycle can vary from 50% as long as each half cycle is at least 6ns. The lower limit of the LTC1748 sample rate is determined by droop of the sample-and-hold circuits. The pipelined architecture of this ADC relies on storing analog signals on small valued capacitors. Junction leakage will discharge the capacitors. The specified minimum operating frequency for the LTC1748 is 1Msps. DIGITAL OUTPUTS
Digital Output Buffers Figure 9 shows an equivalent circuit for a single output buffer. Each buffer is powered by OVDD and OGND, isolated from the ADC power and ground. The additional N-channel transistor in the output driver allows operation down to low voltages. The internal resistor in series with the output makes the output appear as 50 to external circuitry and may eliminate the need for external damping resistors. Output Loading As with all high speed/high resolution converters the digital output loading can affect the performance. The digital outputs of the LTC1748 should drive a minimal capacitive load to avoid possible interaction between the digital outputs and sensitive input circuitry. The output should be buffered with a device such as an ALVCH16373 CMOS latch. For full speed operation the capacitive load should be kept under 10pF. A resistor in series with the
VDD
DATA FROM LATCH OE
PREDRIVER LOGIC
Figure 9. Equivalent Circuit for a Digital Output Buffer
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output may be used but is not required since the ADC has a series resistor of 43 on chip. Lower OVDD voltages will also help reduce interference from the digital outputs. Format The LTC1748 parallel digital output can be selected for offset binary or 2's complement format. The format is selected with the MSBINV pin; high selects offset binary. Overflow Bit An overflow output bit indicates when the converter is overranged or underranged. When OF outputs a logic high the converter is either overranged or underranged. Output Clock The ADC has a delayed version of the ENC input available as a digital output, CLKOUT. The CLKOUT pin can be used to synchronize the converter data to the digital system. This is necessary when using a sinusoidal encode. Data will be updated just after CLKOUT falls and can be latched on the rising edge of CLKOUT. Output Driver Power Separate output power and ground pins allow the output drivers to be isolated from the analog circuitry. The power supply for the digital output buffers, OVDD, should be tied to the same power supply as for the logic being driven. For example if the converter is driving a DSP powered by a 3V supply then OVDD should be tied to that same 3V supply.
LTC1748 VDD OVDD 0.5V TO VDD 0.1F OVDD 43 TYPICAL DATA OUTPUT OGND
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LTC1748
APPLICATIO S I FOR ATIO
OVDD can be powered with any voltage up to 5V. The logic outputs 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 and CLKOUT. The data access and bus relinquish times are too slow to allow the outputs to be enabled and disabled during full speed operation. The output Hi-Z state is intended for use during long periods of inactivity. The voltage on OE can swing between GND and OVDD. OE should not be driven above OVDD. GROUNDING AND BYPASSING The LTC1748 requires a printed circuit board with a clean unbroken ground plane. A multilayer board with an internal ground plane is recommended. The pinout of the LTC1748 has been optimized for a flowthrough layout so that the interaction between inputs and digital outputs is minimized. Layout for the printed circuit board should ensure that digital and analog signal lines are separated as much as possible. In particular, care should be taken not to run any digital track alongside an analog signal track or underneath the ADC. High quality ceramic bypass capacitors should be used at the VDD, VCM, REFHA, REFHB, REFLA and REFLB pins as shown in the block diagram on the front page of this data sheet. Bypass capacitors must be located as close to the pins as possible. Of particular importance are the capacitors between REFHA and REFLB and between REFHB and REFLA. These capacitors should be as close to the device as possible (1.5mm or less). Size 0402 ceramic capacitors are recomended. The large 4.7F capacitor between REFHA and REFLA can be somewhat further away. The traces connecting the pins and bypass capacitors must be kept short and should be made as wide as possible.
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The LTC1748 differential inputs should run parallel and close to each other. The input traces should be as short as possible to minimize capacitance and to minimize noise pickup. An analog ground plane separate from the digital processing system ground should be used. All ADC ground pins labeled GND should connect to this plane. All ADC VDD bypass capacitors, reference bypass capacitors and input filter capacitors should connect to this analog plane. The LTC1748 has three output driver ground pins, labeled OGND (Pins 27, 38 and 47). These grounds should connect to the digital processing system ground. The output driver supply, OVDD should be connected to the digital processing system supply. OVDD bypass capacitors should bypass to the digital system ground. The digital processing system ground should be connected to the analog plane at ADC OGND (Pin 38). HEAT TRANSFER Most of the heat generated by the LTC1748 is transferred from the die through the package leads onto the printed circuit board. In particular, ground pins 12, 13, 36 and 37 are fused to the die attach pad. These pins have the lowest thermal resistance between the die and the outside environment. It is critical that all ground pins are connected to a ground plane of sufficient area. The layout of the evaluation circuit shown on the following pages has a low thermal resistance path to the internal ground plane by using multiple vias near the ground pins. A ground plane of this size results in a thermal resistance from the die to ambient of 35C/W. Smaller area ground planes or poorly connected ground pins will result in higher thermal resistance.
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Evaluation Circuit Schematic of the LTC1748
5V R5 1 3 IN TAB GND JP2 C28 0.1F J2 3201S-40G1 CLKOUT 2 C4 4.7F C23 0.1F CLKOUT R9 33 OUT 4 U2 10T74ALVC1G86 3V 1 3V R8 0 R1** 0 R2 24.9 1 C8 4.7F 2 VCM OGND 2D8 2Q8 2Q7 GND 2Q6 2Q5 VCC 2Q4 2Q3 GND 2Q2 2Q1 1Q8 1D7 39 40 C10 0.1F 41 42 43 44 29 28 D0 OGND CLKOUT ENC OE 27 26 ENC 25 E1 5V 45 46 47 48 GND 1D6 1D5 VCC 1D4 1D3 GND 1D2 1D1 1LE 1Q7 GND 1Q6 1Q5 VCC 1Q4 1Q3 GND 1Q2 1Q1 1OE 15 14 13 12 1D8 11 10 9 8 7 6 5 4 3 2 1 RN8C 33 RN8A 33 RN8B 33 RN7C 33 RN7D 33 RN6C 33 RN6D 33 RN7A 33 RN7B 33 38 16 17 18 RN6A 33 RN6B 33 19 RN5D 33 20 RN5C 33 21 22 RN5B 33 2D7 GND 2D6 2D5 VCC 2D4 2D3 GND 2D2 2D1 D13 D12 D11 OVDD D10 D9 D8 D7 OGND GND GND D6 D5 D4 OVDD D3 D2 D1 30 31 32 33 34 35 36 37 37 36 38 35 39 34 40 33 41 32 42 31 43 C12 0.1F 30 44 29 45 28 46 27 GND AIN+ AIN- GND VDD VDD GND REFLB REFHA GND GND REFLA REFHB GND VDD VDD GND VDD GND MSBINV 47 23 26 3 C13 0.1F 4 5 C18 R B 4.7F 24.9 6 7 8 RX* C26 0.1F 10 11 C8 4.7F C9 0.1F 14 15 R22 100 C27 0.1F 17 18 C14 4.7F 19 20 21 22 23 24 5V JP3 JP4 RY* C16 10F E4 PGND C19 0.1F C20 0.1F C21 0.1F C22 0.1F
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LTC1748
J3 ANALOG INPUT SENSE OF 2LE 2OE RN5A 33 48 24 25 R4 100 R7 24.9 R10** 0 C25 12pF C5 12pF
R3 100
*
*
APPLICATIO S I FOR ATIO
J4 OPTIONAL - INPUT
9
C7 0.1F 13
12
ENCODE INPUT
T2 MINICIRCUITS T1-1T
J5
*
16
R21 100 JP5 OPTIONAL XTAL CLK C15 0.1F
*
C11 1F
1
C30 5V 0.1F 14
C31 0.1F
4
Y1
11
7
8
R6 200 C32 30pF
C2 0.1F
JP1
C17 0.1F
E3 GND
E4 GND
E5 GND
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*RX, RY = OPTIONAL INPUT RANGE SET **DO NOT INSTALL R1 AND R10
INPUT TWOS RANGE COMPLEMENT SELECT SELECT
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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
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C29 1F
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U3 LT1521-3 C3 10F RA 24.9 C24 12pF U5 LTC1748 U4 P174VCX16373V C1 2F
J1 OPTIONAL +INPUT
T1 MINICIRCUITS T1-1T
LTC1748
APPLICATIO S I FOR ATIO
Silkscreen Top
Layer 2 GND Plane
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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Layer 1 Component Side Layer 3 Power Plane Layer 4 Solder Side
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LTC1748
PACKAGE DESCRIPTIO
0.95 0.10
8.1 0.10
6.2 0.10 7.9 - 8.3 (.311 - .327)
0.32 0.05
0.50 TYP 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 1.20 (.0473) MAX 0 - 8 -C-T.10 C 0.05 - 0.15 (.002 - .006)
FW48 TSSOP 0502
RECOMMENDED SOLDER PAD LAYOUT 6.0 - 6.2** (.236 - .244)
0.09 - 0.20 (.0035 - .008)
0.45 - 0.75 (.018 - .029)
NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 3. DRAWING NOT TO SCALE *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .152mm (.006") PER SIDE **DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE
RELATED PARTS
PART NUMBER LTC1405 LTC1406 LTC1411 LTC1412 LTC1414 LTC1420 LTC1461 LTC1666 LTC1667 LTC1668 LTC1741 LTC1742 LTC1743 LTC1744 LTC1745 LTC1746 LTC1747 LT(R)1807 DESCRIPTION 12-Bit, 5Msps Sampling ADC with Parallel Output 8-Bit, 20Msps ADC 14-Bit, 2.5Msps ADC 12-Bit, 3Msps, Sampling ADC 14-Bit, 2.2Msps ADC 12-Bit, 10Msps ADC Micropower Precision Series Reference 12-Bit, 50Msps DAC 14-Bit, 50Msps DAC 16-Bit, 50Msps DAC 12-Bit, 65Msps ADC 14-Bit, 65Msps ADC 12-Bit, 50Msps ADC 14-Bit, 50Msps ADC 12-Bit, 25Msps ADC 14-Bit, 25Msps ADC 12-Bit, 80Msps ADC 325MHz, Low Distortion Dual Op Amp COMMENTS Pin Compatible with the LTC1420 Undersampling Capability up to 70MHz 5V, No Pipeline Delay, 80dB SINAD 5V, No Pipeline Delay, 72dB SINAD 5V, 81dB SINAD and 95dB SFDR 71dB SINAD and 83dB SFDR at Nyquist 0.04% Max Initial Accuracy, 3ppm/C Drift Pin Compatible with the LTC1668, LTC1667 Pin Compatible with the LTC1668, LTC1666 16-Bit, No Missing Codes, 90dB SINAD, -100dB THD Pin Compatible with the LTC1748 Pin Compatible with the LTC1748 Pin Compatible with the LTC1748 Pin Compatible with the LTC1748 Pin Compatible with the LTC1748 Pin Compatible with the LTC1748 Pin Compatible with the LTC1748 Rail-to-Rail Input and Output
1748fa LT/TP 1103 1K REV A * PRINTED IN THE USA
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
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FW Package 48-Lead Plastic TSSOP (6.1mm)
(Reference LTC DWG # 05-08-1651)
12.4 - 12.6* (.488 - .496) 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 0.50 (.0197) BSC 0.17 - 0.27 (.0067 - .0106)
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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