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PDF ADS800 Data sheet ( Hoja de datos )
| Número de pieza | ADS800 | |
| Descripción | 12-Bit/ 40MHz Sampling ANALOG-TO-DIGITAL CONVERTER | |
| Fabricantes | Burr-Brown Corporation | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de ADS800 (archivo pdf) en la parte inferior de esta página. Total 14 Páginas | ||
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®
ADS800U
ADS800E
ADS800
TM 12-Bit, 40MHz Sampling
ANALOG-TO-DIGITAL CONVERTER
FEATURES
q LOW POWER: 390mW
q INTERNAL REFERENCE
q WIDEBAND TRACK/HOLD: 65MHz
q SINGLE +5V SUPPLY
q PACKAGE: 28-Lead SOIC and
28-Lead SSOP
APPLICATIONS
q IF AND BASEBAND DIGITIZATION
q DIGITAL COMMUNICATIONS
q ULTRASOUND IMAGING
q GAMMA CAMERAS
q TEST INSTRUMENTATION
q CCD IMAGING
Copiers
Scanners
Cameras
q VIDEO DIGITIZING
IN
IN
REFT
CM
REFB
DESCRIPTION
The ADS800 is a low power, monolithic 12-bit, 40MHz
analog-to-digital converter utilizing a small geometry
CMOS process. This COMPLETE converter includes
a 12-bit quantizer, wideband track/hold, reference and
three-state outputs. It operates from a single +5V
power supply and can be configured to accept either
differential or single-ended input signals.
The ADS800 employs digital error correction to pro-
vide excellent Nyquist differential linearity perfor-
mance for demanding imaging applications. Its low
distortion, high SNR and high oversampling capability
give it the extra margin needed for telecommunications,
test instrumentation and video applications.
This high performance A/D converter is specified over
temperature for AC and DC performance at a 40MHz
sampling rate. The ADS800 is available in 28-lead
SOIC and SSOP packages.
CLK
MSBI
OE
Timing
Circuitry
T/H
+3.25V
Pipeline
A/D
Error
Correction
Logic
3-State
Outputs
12-Bit
Digital
Data
+1.25V
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111
Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
©1995 Burr-Brown Corporation
PDS-1286E
Printed in U.S.A. November, 1996
1 page  
TYPICAL PERFORMANCE CURVES
At TA = +25°C, VS = +5V, Sampling Rate = 40MHz, with a 50% duty cycle clock having a 2ns rise/fall time, unless otherwise noted.
0
–20
–40
–60
–80
–100
–120
0
SPECTRAL PERFORMANCE
fIN = 500kHz
5 10 15
Frequency (MHz)
20
0
–20
–40
–60
–80
–100
–120
0
SPECTRAL PERFORMANCE
fIN = 1MHz
5 10 15
Frequency (MHz)
20
0
–20
–40
–60
–80
–100
–120
0
SPECTRAL PERFORMANCE
fIN = 5MHz
5 10 15
Frequency (MHz)
20
0
–20
–40
–60
–80
–100
–120
0
SPECTRAL PERFORMANCE
fIN = 12MHz
5 10 15
Frequency (MHz)
20
0
–20
–40
–60
–80
–100
–120
0
SPECTRAL PERFORMANCE
fIN = 1MHz
fS = 10MHz
1.0 2.0 3.0 4.0
Frequency (MHz)
5.0
0
–20
–40
–60
–80
–100
–120
0.0
TWO-TONE INTERMODULATION
f1 = 12.5MHz
f2 = 12.0MHz
5.0 10.0
Frequency (MHz)
15.0
20.0
®
5 ADS800
5 Page 
APPLICATIONS
DRIVING THE ADS800
The ADS800 has a differential input with a common-mode
of +2.25V. For AC-coupled applications, the simplest way to
create this differential input is to drive the primary winding
of a transformer with a single-ended input. A differential
output is created on the secondary if the center tap is tied to
the common-mode voltage of +2.25V per Figure 5. This
transformer-coupled input arrangement provides good high
frequency AC performance. It is important to select a trans-
former that gives low distortion and does not exhibit core
saturation at full scale voltage levels. Since the transformer
does not appreciably load the ladder, there is no need to
buffer the common-mode (CM) output in this instance. In
general, it is advisable to keep the current draw from the CM
output pin below 0.5µA to avoid nonlinearity in the internal
reference ladder. A FET input operational amplifier such as
the OPA130 can provide a buffered reference for driving
external circuitry. The analog IN and IN inputs should be
bypassed with 22pF capacitors to minimize track/hold glitches
and to improve high input frequency performance.
Figure 6 illustrates another possible low cost interface circuit
which utilizes resistors and capacitors in place of a trans-
former. Depending on the signal bandwidth, the component
values should be carefully selected in order to maintain the
AC Input
Signal
22 CM
0.1µF
22pF
26 IN
ADS800
Mini-Circuits
T T1-6-KK81
or equivalent
22pF
27 IN
FIGURE 5. AC-Coupled Single-Ended to Differential Drive
Circuit Using a Transformer.
performance outlined in the data sheet. The input capacitors,
CIN, and the input resistors, RIN, create a high-pass filter with
the lower corner frequency at fC = 1/(2πRINCIN). The corner
frequency can be reduced by either increasing the value of
RIN or CIN. If the circuit operates with a 50Ω or 75Ω
impedance level, the resistors are fixed and only the value of
the capacitor can be increased. Usually AC-coupling capaci-
tors are electrolytic or tantalum capacitors with values of
1µF or higher. It should be noted that these large capacitors
become inductive with increased input frequency, which
could lead to signal amplitude errors or oscillation. To
maintain a low AC-coupling impedance throughout the sig-
nal band, a small value (e.g. 1µF) ceramic capacitor could be
added in parallel with the polarized capacitor.
Capacitors CSH1 and CSH2 are used to minimize current
glitches resulting from the switching in the input track and
hold stage and to improve signal-to-noise performance. These
capacitors can also be used to establish a low-pass filter and
effectively reduce the noise bandwidth. In order to create a
real pole, resistors RSER1 and RSER2 were added in series with
each input. The cut-off frequency of the filter is determined
by fC = 1/(2πRSER•(CSH+CADC)) where RSER is the resistor in
series with the input, CSH is the external capacitor from the
input to ground, and CADC is the internal input capacitance of
the A/D converter (typically 4pF).
Resistors R1 and R2 are used to derive the necessary common
mode voltage from the buffered top and bottom references.
The total load of the resistor string should be selected so that
the current does not exceed 1mA. Although the circuit in
Figure 6 uses two resistors of equal value so that the common
mode voltage is centered between the top and bottom refer-
ence (+2.25V), it is not necessary to do so. In all cases the
center point, VCM, should be bypassed to ground in order to
provide a low impedance AC ground.
If the signal needs to be DC coupled to the input of the
ADS800, an operational amplifier input circuit is required.
In the differential input mode, any single-ended signal must
be modified to create a differential signal. This can be
CIN
0.1µF
RIN1
25Ω
RIN2
25Ω
CIN
0.1µF
*RSER1
49.9Ω
R3
1kΩ
C2
0.1µF
*RSER2
49.9Ω
NOTE: * indicates optional component.
FIGURE 6. AC-Coupled Differential Input Circuit.
R1
(6kΩ)
CSH1
22pF
VCM
C1
0.1µF
IN
+3.25V
Top Reference
ADS8xx
R2
(6kΩ)
CSH2
22pF
IN
C3
0.1µF
+1.25V
Bottom Reference
11 ADS800
®
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet ADS800.PDF ] | |
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