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PDF LTC1420IGN Data sheet ( Hoja de datos )
| Número de pieza | LTC1420IGN | |
| Descripción | 12-Bit/ 10Msps/ Sampling ADC | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s 10Msps Sample Rate
s Single 5V Supply or ±5V Supplies
s Integral Nonlinearity Error <0.35LSB
s Differential Nonlinearity <0.25LSB
s 71dB S/(N + D) and 83dB SFDR at Nyquist
s 100MHz Full-Power Bandwidth Sampling
s ±2.048V, ±1.024V and ±0.512V Bipolar Input Range
s Input PGA
s Out-of-Range Indicator
s True Differential Inputs with 75dB CMRR
s Power Dissipation: 250mW
s 28-Pin Narrow SSOP Package
U
APPLICATIO S
s Telecommunications
s Digital Signal Processing
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.
LTC1420
12-Bit, 10Msps,
Sampling ADC
DESCRIPTIO
The LTC®1420 is a 10Msps, 12-bit sampling A/D converter
that draws only 250mW from either single 5V or dual ±5V
supplies. This easy-to-use device includes a high dynamic
range sample-and-hold, a precision reference and a PGA
input circuit.
The LTC1420 has a flexible input circuit that allows full-
scale input ranges of ±2.048V ±1.024V and ±0.512V. The
input common mode voltage is arbitrary, though a 2.5V
reference is provided for single supply applications. The
input PGA has a digitally selectable 1x or 2x gain.
Maximum DC specs include ±1LSB INL and ±1LSB DNL
over temperature. Outstanding AC performance includes
71dB S/(N + D) and 83dB SFDR at the Nyquist input
frequency of 5MHz.
The unique differential input sample-and-hold can acquire
single-ended or differential input signals up to its 100MHz
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.
TYPICAL APPLICATIO
5V
+ 1 +AIN
VIN
– 2 –AIN
28
GAIN
S/H
3 VCM
1µF
MODE SELECT
4 SENSE
5 VREF
1µF
5V 5V
1µF 1µF
7 23
VDD VDD
1µF
22
OVDD
OPTIONAL 3V
LOGIC SUPPLY
PIPELINED 12-BIT ADC
DIGITAL CORRECTION
LOGIC
2.5V
REFERENCE
2.048V
OF 27
D11 (MSB) 10
OUTPUT
BUFFERS
D0 (LSB) 20
DIGITAL
OUTPUT
CLK 26 10MHz CLK
VSS
25
1µF 0V OR –5V
GND GND
68
GND
24
OGND
21
1420 TA01
1.00
0.75
0.50
0.25
0
–0.25
–0.50
–0.75
–1.00
0
Typical INL Curve
1024
2048
CODE
3072
4096
1420 TA02
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC1420
S/(N+D) vs Input Frequency
and Amplitude
75
VIN = 0dB
70
VIN = –6dB
65
DUAL SUPPLIES
60 ±2.048V RANGE
GAIN = 1×
55
VIN = –20dB
50
0.1
1 10
INPUT FREQUENCY (MHz)
100
1420 G01
S/(N+D) vs Input Frequency
and Amplitude
75
SINGLE SUPPLY
70
VIN = 0dB
±1.024V RANGE
GAIN = 2×
VIN = –6dB
65
60
55
50
0.1
VIN = –20dB
1 10
INPUT FREQUENCY (MHz)
100
1420 G02
SFDR vs Input Frequency,
Differential Input
–50
DUAL SUPPLIES
–55 ±2.048V RANGE
–60
GAIN = 1×
AIN = 0dBFS
–65
–70
–75
–80
–85
–90
–95
–100
0.1
1 10
INPUT FREQUENCY (MHz)
100
1420 F07
Spurious-Free Dynamic Range
vs Input Amplitude
100
dBFS
90
80
dBc
70
60
50
40
–50
DUAL SUPPLIES
±2.048V RANGE
GAIN = 1×
fIN = 5MHz
–40 –30 –20 –10
INPUT AMPLITUDE (dBFS)
0
1420 G03
Spurious-Free Dynamic Range
vs Input Amplitude
100
dBFS
90
80
dBc
70
60
50
40
–50
SINGLE SUPPLY
±1.024V RANGE
GAIN = 2×
fIN = 5MHz
–40 –30 –20 –10
INPUT AMPLITUDE (dBFS)
0
1420 G05
SFDR vs Input Frequency,
Differential Input
–50
SINGLE SUPPLY
–55 ±1.024V RANGE
–60
GAIN = 2×
AIN = 0dBFS
–65
–70
–75
–80
–85
–90
–95
–100
0.1
1 10
INPUT FREQUENCY (MHz)
100
1420 F08
Distortion vs Input Frequency
–50
DUAL SUPPLIES
–55 ±2.048V RANGE
GAIN = 1×
–60 AIN = 0dBFS
–65
–70
–75
–80
THD
–85
3RD 2ND
–90
–95
0
1 10
INPUT FREQUENCY (MHz)
100
1420 G04
Distortion vs Input Frequency
–50
SINGLE SUPPLY
–55 ±1.024V RANGE
GAIN = 2×
–60 AIN = 0dBFS
–65
–70
–75
–80
THD 3RD
–85
2ND
–90
–95
0
1 10
INPUT FREQUENCY (MHz)
100
1420 G06
Grounded Input Histogram
VREF = 4.096V 410554
GAIN = 1×
1570
N–1
N
CODE
1572
N+1
1420 F09
5
5 Page 
LTC1420
APPLICATIONS INFORMATION
Differential Operation
The THD and SFDR performance of the LTC1420 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 LTC1420 on the printed
circuit board.
MINI CIRCUITS
T1-1T
15Ω
VIN 470pF
15Ω
1µF
5V
+AIN
LTC1420
–AIN
VCM VSS
1420 F08a
Figure 8a. Single Supply Transformer Coupled Input
MINI CIRCUITS
T1-1T
15Ω
VIN 470pF
15Ω
5V
+AIN
LTC1420
–AIN
1µF
VCM VSS
1420 F08b
–5V
Figure 8b. Dual Supply Transformer Coupled Input
Choosing an Input Amplifier
Choosing an input amplifier is easy if a few requirements
are taken into consideration. First, to limit the magnitude
of the voltage spike seen by the amplifier from charging
the sampling capacitor, choose an amplifier that has a low
output impedance (<100Ω) at the closed-loop bandwidth
frequency. For example, if an amplifier is used in a gain of
1 and has a unity-gain bandwidth of 100MHz, then the
output impedance at 100MHz must be less than 100Ω.
The second requirement is that the closed-loop bandwidth
must be greater than 100MHz to ensure adequate small-
signal settling for full throughput rate. If slower op amps
are used, more settling time can be provided by increasing
the time between conversions.
The best choice for an op amp to drive the LTC1420 will
depend on the application. Generally applications fall into
two categories: AC applications where dynamic specifica-
tions are most critical and time domain applications where
DC accuracy and settling time are most critical.
Input Filtering
The noise and the distortion of the input amplifier and
other circuitry must be considered since they will add to
the LTC1420 noise and distortion. The small-signal band-
width of the sample-and-hold circuit is 100MHz. Any noise
or distortion products that are present at the analog inputs
will be summed over this entire bandwidth. Noisy input
circuitry should be filtered prior to the analog inputs to
minimize noise. A simple 1-pole RC filter is sufficient for
many applications.
For example, Figure 9 shows a 470pF capacitor from + AIN
to – AIN and a 30Ω source resistor to limit the input
bandwidth to 11.3MHz. The 470pF capacitor also acts as
a charge reservoir for the input sample-and-hold and
isolates the amplifier driving VIN from the ADC’s small
current glitch. In undersampling applications, an input
capacitor this large may prohibitively limit the input band-
width. If this is the case, use as large an input capacitance
as possible. High quality capacitors and resistors should
be used since these components can add distortion. NPO
and silver mica type dielectric capacitors have excellent
linearity. Carbon surface mount resistors can generate
distortion from self-heating and from damage that may
occur during soldering. Metal film surface mount resis-
tors are much less susceptible to both problems.
30Ω
VIN
470pF
+AIN
LTC1420
–AIN
Figure 9. RC Input Filter
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC1420IGN.PDF ] | |
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