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PDF LTC1740 Data sheet ( Hoja de datos )
| Número de pieza | LTC1740 | |
| Descripción | 14-Bit 6Msps Sampling ADC | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s 6Msps Sample Rate
s 79dB S/(N + D) and 91dB SFDR at 2.5MHz fIN
s Single 5V Supply or ±5V Supplies
s Integral Nonlinearity Error: < 1LSB
s Differential Nonlinearity: < 0.5LSB
s 80MHz Full-Power Bandwidth Sampling
s ±2.5V and ±1.25V Bipolar Input Ranges
s 2.5V Signal Ground Available
s Out-of-Range Indicator
s True Differential Inputs with 75dB CMRR
s Power Dissipation: 245mW
s 36-Pin SSOP Package (0.209 Inch Width)
U
APPLICATIO S
s Telecommunications
s Multiplexed Data Acquisition Systems
s High Speed Data Acquisition
s Spectral Analysis
s Imaging Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTC1740www.DataSheet4U.com
14-Bit, 6Msps,
Sampling ADC
DESCRIPTIO
The LTC®1740 is a 6Msps, 14-bit sampling A/D converter
that draws only 245mW from either a single 5V or dual
±5V supplies. This easy-to-use device includes a high
dynamic range sample-and-hold and a programmable
precision reference.
The LTC1740 has a flexible input circuit that allows differ-
ential full-scale input ranges of ±2.5V and ±1.25V with the
internal reference, or any full-scale input range up to
±2.5V with an external reference. The input common
mode voltage is arbitrary, though a 2.5V reference is
provided for single supply applications.
DC specifications include 1LSB typical INL, 0.5LSB typical
DNL and no missing codes over temperature. Outstanding
AC performance includes 79dB S/(N␣ +␣ D) and 91dB SFDR
at an input frequency of 2.5MHz.
The unique differential input sample-and-hold can acquire
single-ended or differential input signals up to its 80MHz
bandwidth. The 75dB common mode rejection allows
users to eliminate ground loops and common mode noise
by measuring signals differentially from the source. A
separate output logic supply allows direct connection to
3V components.
BLOCK DIAGRA
5V 5V
3V TO 5V
+
VIN 1000pF
–
1µF
1µF
1µF 1µF
+AIN
1
89
VDD VDD
32 33
VDD VDD
–AIN
2
VCM
3
S/H
PIPELINED 14-BIT ADC
MODE SELECT
SENSE
4
5 VREF
DIGITAL CORRECTION
LOGIC
2.5V
REFERENCE
2.250V
1µF
19
OVDD
OF
36
D13 (MSB)
12
OUTPUT
BUFFERS
D7
18
D6
20
DIGITAL
OUTPUT
D0 (LSB)
26
BUSY
27
CLK
35
6MHz CLK
VSS VSS
30 29
GND GND GND GND GND OGND OGND
6 7 10 34 31 11 28 1740 TA01
1µF 0V OR –5V
4096-Point FFT
0
fSMPL = 6MHz
fIN = 2.5MHz, 5VP-P
–20 5V SUPPLY
–40
–60
–80
–100
–120
0
0.5 1.0 1.5 2.0 2.5 3.0
FREQUENCY (MHz)
1740 TA02
1740f
1
1 page  
WU
TI I G 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 ground with GND and OGND
wired together (unless otherwise noted).
Note 3: When these pin voltages are taken below VSS or above VDD, they
will be clamped by internal diodes. This product can handle input currents
greater than 100mA below VSS or above VDD without latchup.
Note 4: VDD = 5V, VSS = –5V or 0V, fSAMPLE = 6MHz, tr = tf = 5ns unless
otherwise specified.
Note 5: Linearity, offset and full-scale specifications apply for a
single-ended +AIN input with – AIN tied to VCM for single supply and 0V for
dual supply.
LTC1740www.DataSheet4U.com
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 –0.5LSB
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
Typical INL at 6Msps
2.0
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
0
4096
8192
CODE
12288 16384
1740 G01
S/(N + D) vs Input Frequency
and Amplitude
80
VIN = 0dBFS
75
VIN = –6dBFS
70
65
VIN = –20dBFS
60
SINGLE SUPPLY
55 5V INPUT RANGE
DIFFERENTIAL INPUT
6Msps
50
0.1
1
10
INPUT FREQUENCY (MHz)
100
1740 G04
Typical DNL at 6Msps
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
0
4096
8192
CODE
12288 16384
1740 G02
SFDR and THD
vs Input Frequency
95
90
SFDR
85
–THD
80
75
70
65 DUAL SUPPLIES
60 5V INPUT RANGE
AIN = 0dBFS
55 DIFFERENTIAL INPUT
6Msps
50
0.1 1 10
INPUT FREQUENCY (MHz)
100
1740 G05
S/(N + D) vs Input Frequency
and Amplitude
80
VIN = 0dBFS
75
VIN = –6dBFS
70
65
VIN = –20dBFS
60
DUAL SUPPLIES
55 5V INPUT RANGE
DIFFERENTIAL INPUT
6Msps
50
0.1
1
10
INPUT FREQUENCY (MHz)
100
1740 G03
SFDR and THD
vs Input Frequency
95
90
SFDR
85
–THD
80
75
70
65 SINGLE SUPPLY
60 5V INPUT RANGE
AIN = 0dBFS
55 DIFFERENTIAL INPUT
6Msps
50
0.1 1 10
INPUT FREQUENCY (MHz)
100
1740 G06
1740f
5
5 Page 
APPLICATIO S I FOR ATIO
5V
0V VIN
+AIN
LTC1740
–AIN
VCM VSS
1µF
1405 F04
–5V
Figure 4. DC Coupling a Ground Centered Signal
(Dual Supply System)
2.5V VIN
5V
+AIN
LTC1740
–AIN
VCM VSS
1µF
1740 F05
LTC1740www.DataSheet4U.com
5V
C
0V VIN
+AIN
LTC1740
RR
C
–AIN
VCM VSS
1µF
1740 F07
Figure 7. AC Coupling to the LTC1740. Note That the Input Signal
Can Almost Always Be Directly Coupled with Better Performance
MINI CIRCUITS
T1-1T
15Ω
VIN 1000pF
15Ω
1µF
5V
+AIN
LTC1740
–AIN
VCM VSS
1740 F08a
Figure 5. DC Coupling a Signal Centered Around
2.5V (Single Supply System)
2.500V
0V
5V
VIN
1.25V
1µF
5V
+AIN
LTC1740
–AIN
VREF
SENSE
VSS
1740 F06
Figure 6. DC Coupling a 0V to 2.5V Signal
AC Coupling the Input
The analog inputs to the LTC1740 can also be AC coupled
through a capacitor, though in most cases it is simpler to
directly couple the input to the ADC. Figure 7 shows an
example where the input signal is centered around ground
and the ADC operates from a single 5V supply. Note that
the performance would improve if the ADC was operated
from a dual supply and the input was directly coupled (as
in Figure 4). With AC coupling the DC resistance to ground
should be roughly matched for AIN+ and AIN– to maintain
offset accuracy.
Figure 8a. Single Supply Transformer Coupled Input
MINI CIRCUITS
T1-1T
15Ω
VIN 1000pF
15Ω
1µF
5V
+AIN
LTC1740
–AIN
VCM VSS
1740 F08b
–5V
Figure 8b. Dual Supply Transformer Coupled Input
Differential Operation
The THD and SFDR performance of the LTC1740 can be
improved by using a center tap RF transformer to drive the
inputs differentially. Though the signal can no longer be
DC coupled, the improvement in dynamic performance
makes this an attractive solution for some applications.
Typical connections for single and dual supply systems
are shown in Figures 8a and 8b. Good choices for trans-
formers are the Mini Circuits T1-1T (1:1 turns ratio) and
T4-6T (1:4 turns ratio). For best results the transformer
should be located close to the LTC1740 on the printed
circuit board.
1740f
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC1740.PDF ] | |
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