LTC1748 Linear Technology, LTC1748 Datasheet

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LTC1748

Manufacturer Part Number
LTC1748
Description
14-Bit 80Msps Low Noise ADC
Manufacturer
Linear Technology
Datasheet

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FEATURES
BLOCK DIAGRA
APPLICATIO S
, LTC and LT are registered trademarks of Linear Technology Corporation.
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
Telecommunications
Receivers
Cellular Base Stations
Spectrum Analysis
Imaging Systems
ANALOG INPUT
DIFFERENTIAL
4.7 F
1V
SENSE
U
A
A
V
IN
IN
CM
+
2.35V
SELECT
RANGE
W
REF
BUFFER
80Msps, 14-Bit ADC with a 2V Differential Input Range
AMP
S/H
DIFF AMP
0.1 F
REFLB
1 F
PIPELINED ADC
14-BIT
14-Bit, 80Msps Low Noise ADC
REFHA
DESCRIPTIO
The LTC
verter designed for digitizing high frequency, wide dy-
namic 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 0.15ps
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.
4.7 F
REFLA
1 F
®
0.1 F
RMS
1748 is an 80Msps, sampling 14-bit A/D con-
REFHB
ENCODE INPUT
DIFFERENTIAL
allows undersampling of IF frequencies with
CORRECTION
LOGIC AND
REGISTER
ENC
SHIFT
CONTROL LOGIC
ENC
U
14
MSBINV
LATCHES
OUTPUT
OE
GND
OV
OGND
V
1748 BD
www.DataSheet4U.com
DD
DD
OF
D13
D0
CLKOUT
0.1 F
1 F
1 F
0.1 F
LTC1748
1 F
0.5V
TO 5V
5V
1748fa
1

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LTC1748 Summary of contents

Page 1

... 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 ...

Page 2

... Digital Output Voltage ................. – 0. OGND Voltage ..............................................– 0. Power Dissipation ............................................ 2000mW Operating Temperature Range LTC1748C ............................................... LTC1748I ............................................ – Storage Temperature Range ................. – 150 C Lead Temperature (Soldering, 10 sec).................. 300 VERTER CHARACTERISTICS temperature range, otherwise specifications are at T ...

Page 3

... Input Signal, First 5 Harmonics (3.2V Range 2.52MHz 5.2MHz (2V Range) IN1 IN2 f = 2.52MHz 5.2MHz (3.2V Range) IN1 IN2 SOURCE (Note 5) CONDITIONS OUT OUT 4.75V V 5.25V DD 1mA I 1mA OUT LTC1748 www.DataSheet4U.com MIN TYP MAX UNITS 72 76 76.1 dB 72.2 dB 75.4 dB 71 ...

Page 4

... LTC1748 U U DIGITAL I PUTS A D DIGITAL OUTPUTS operating temperature range, otherwise specifications are at T SYMBOL PARAMETER V High Level Input Voltage IH V Low Level Input Voltage IL I Digital Input Current IN C Digital Input Capacitance IN V High Level Output Voltage OH V Low Level Output Voltage ...

Page 5

... FREQUENCY (MHz) LTC1748 www.DataSheet4U.com = 5V 80MHz, differential ENC/ENC = 2V SAMPLE 8192 Point FFT, Input Frequency = 15.068MHz, –1dB, 3.2V Range –10 –20 –30 –40 –50 –60 –70 –80 – ...

Page 6

... LTC1748 W U TYPICAL PERFOR A CE CHARACTERISTICS 8192 Point FFT, Input Frequency = 30.068MHz, –10dB, 3.2V Range –10 –20 –30 –40 –50 –60 –70 –80 –90 –100 –110 –120 FREQUENCY (MHz) 1748 G07 8192 Point FFT, Input Frequency = 40.64MHz, – ...

Page 7

... INPUT LEVEL (dBFS) 1748 G23 LTC1748 www.DataSheet4U.com 8192 Point 2-Tone FFT, Input Frequency = 5MHz and 7MHz, –7dB, 3.2V Range –10 –20 –30 –40 –50 –60 –70 –80 –90 – ...

Page 8

... LTC1748 W U TYPICAL PERFOR A CE CHARACTERISTICS SFDR vs Input Frequency and Amplitude, 3.2V Range, 2nd and 3rd Harmonic 100 –20dB 95 –10dB 90 –6dB 85 80 –1dB 100 INPUT FREQUENCY (MHz) 1748 G25 SNR vs Input Frequency 3.2V Range 78 77.5 77.0 76.5 76.0 75.5 75.0 74.5 74 ...

Page 9

... DD ers. Bypass to ground with 0.1 F 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. LTC1748 www.DataSheet4U.com Supply Current vs Sample Rate ...

Page 10

... LTC1748 DIAGRA • N ANALOG INPUT ENC t 7 DATA t 6 CLKOUT DATA U U 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 ...

Page 11

... 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 brev- ity, the text will refer to ENC greater than ENC as ENC high and ENC less than ENC as ENC low ...

Page 12

... 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 ana- log inputs are sampled directly onto sampling capacitors (C ) through CMOS transmission gates ...

Page 13

... Poor matching will result in higher even order harmonics, especially the second. Input Drive Circuits Figure 3 shows the LTC1748 being driven transformer with a center tapped secondary. The second- ary center tap is DC biased with V CM signal at its optimum DC level ...

Page 14

... See the Typical Performance Charac- teristics 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 ...

Page 15

... DD 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 ...

Page 16

... 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 ...

Page 17

... 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 envi- ronment ...

Page 18

... LTC1748 U U APPLICATIO S I FOR ATIO www.DataSheet4U.com 1748fa ...

Page 19

... 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 Layer 4 Solder Side LTC1748 www.DataSheet4U.com Layer 1 Component Side Layer 3 Power Plane 19 1748fa ...

Page 20

... 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 www.linear.com www.DataSheet4U.com 7.9 – ...

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