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ADS2806Y Schematic ( PDF Datasheet ) - Burr-Brown Corporation

Teilenummer ADS2806Y
Beschreibung Dual/ 12-Bit/ 32MHz Sampling ANALOG-TO-DIGITAL CONVERTER
Hersteller Burr-Brown Corporation
Logo Burr-Brown Corporation Logo 




Gesamt 19 Seiten
ADS2806Y Datasheet, Funktion
ADS2806
ADS2806
SBAS178B – DECEMBER 2000 – REVISED MAY 2002
Dual, 12-Bit, 32MHz Sampling
ANALOG-TO-DIGITAL CONVERTER
FEATURES
q SPURIOUS-FREE DYNAMIC RANGE:
73dB at 10MHz fIN
q HIGH SNR: 67dB (2Vp-p), 69dB (3Vp-p)
q INTERNAL OR EXTERNAL REFERENCE
q LOW DLE: ±0.4LSB
q FLEXIBLE INPUT RANGE: 2Vp-p to 3Vp-p
q TQFP-64 POWER PACKAGE
DESCRIPTION
The ADS2806 is a dual, high-speed, high dynamic range,
12-bit pipelined Analog-to-Digital Converter (ADC). This con-
verter includes a high-bandwidth track-and-hold that gives
excellent spurious performance up to and beyond the Nyquist
rate. The differential nature of this track-and-hold and ADC
circuitry minimizes even-order harmonics and gives excel-
lent common-mode noise immunity. The track-and-hold can
also be operated single-ended.
The ADS2806 provides for setting the full-scale range of the
converter without any external reference circuitry. The internal
+VS
APPLICATIONS
q COMMUNICATIONS IF PROCESSING
q COMMUNICATIONS BASESTATIONS
q TEST EQUIPMENT
q MEDICAL IMAGING
q VIDEO DIGITIZING
q CCD DIGITIZING
reference can be disabled allowing low drive, external refer-
ences to be used for improved tracking in multichannel systems.
The ADS2806 provides an over-range indicator flag to
indicate an input signal that exceeds the full-scale input
range of the converter. This flag can be used to reduce the
gain of front end gain control circuitry. There is also an
output enable pin to allow for multiplexing and testability on
a PC board.
The ADS2806 employs digital error correction techniques to
provide excellent differential linearity for demanding imag-
ing applications. The ADS2806 is available in a TQFP-64
power package.
OEA OVRA
ADS2806
VIN INA
T&H
INA
(Opt.)
12-Bit
Pipelined
A/D
Error
Correction
Logic
3-State
Outputs
D12A
D1A
INT/EXT
FSSEL
Internal
Reference
Timing
Circuitry
CLK
VIN INB
T&H
INB
(Opt.)
CM
12-Bit
Pipelined
A/D
Error
Correction
Logic
3-State
Outputs
D12B
D1B
Optional External
Reference
OEB OVRB
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
www.ti.com
Copyright © 2000, Texas Instruments Incorporated






ADS2806Y Datasheet, Funktion
TYPICAL CHARACTERISTICS
At TA = full specified temperature range, VS = +5V, differential input range = 2V to 3V for each input, sampling rate = 32MSPS, unless otherwise noted.
0
20
40
60
80
100
120
0
SPECTRAL PERFORMANCE
(Differential, 2Vp-p)
fIN = 1MHz
SFDR = 73.5dBFS
SNR = 67.4dBFS
4 8 12
Frequency (MHz)
16
SPECTRAL PERFORMANCE
(Differential, 2Vp-p)
0
fIN = 10MHz
20
SFDR = 73.1dBFS
SNR = 66dBFS
40
60
80
100
120
0
4 8 12
Frequency (MHz)
16
0
20
40
60
80
100
120
0
SPECTRAL PERFORMANCE
(Differential, 3Vp-p)
fIN = 1MHz
SFDR = 71.3dBFS
SNR = 69.2dBFS
4 8 12
Frequency (MHz)
16
SPECTRAL PERFORMANCE
(Differential, 3Vp-p)
0
fIN = 10MHz
20 SFDR = 70.8dBFS
SNR = 67.9dBFS
40
60
80
100
120
0
4 8 12
Frequency (MHz)
16
2-TONE INTERMODULATION DISTORTION
0
f1 = 9MHz (7dBFS)
20 f2 = 10MHz (7dBFS)
IMD(3) = 74.6dBc
40
60
80
100
120
0
4 8 12
Frequency (MHz)
16
DYNAMIC PERFORMANCE vs CLOCK
80
REF = 2V
78 fIN = 3.5MHz
76
SFDR
74
72
70
68 SNR
66
64
62
60
24 26 28 30 32 34
Frequency (MHz)
36
6 ADS2806
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SBAS178B

6 Page









ADS2806Y pdf, datenblatt
top and bottom references (REFT, REFB) provide an output
voltage of +3.0V and +2.0V, respectively. The CM output of
the ADS2806 is used to bias the inputs of the driving
amplifiers. Using the OPA2681 on a single +5V supply, its
ideal common-mode point is +2.5V, which coincides with
the recommended common-mode input level for the
ADS2806, thus eliminating the need for coupling capacitors
between the amplifiers and the converter.
The addition of a small series resistor (RS) between the
output of the op amps and the input of the ADS2806 will be
beneficial in almost all interface configurations. It will de-
couple the op amps output from the capacitive load and
avoid gain peaking that can result in increased noise. For
best spurious and distortion performance, the resistor value
should be kept below 100. Furthermore, the series resis-
tor, in combination with the shunt capacitor, establishes a
passive low-pass filter limiting the bandwidth for the wideband
noise, thus improving the SNR. The spurious-free dynamic
range of this single-supply front end is limited by the 2nd-
harmonic distortion. An improvement of several dB may be
realized by adding a pull-down resistor (RP) at the output of
each amplifier. This pulls a DC bias current out of the output
stage of the amplifier. It is set to approximately 5mA, see
Figure 3, but will vary depending on the amplifier used.
Single-Ended, AC-Coupled, Dual-Supply Interface
The circuit provided in Figure 4 shows typical connections
for using the ADS2806 in a single-ended input configura-
tion. The bias requirements for AC-coupling are provided by
a single resistor to the CM output lead. The single-ended
mode of operation should be considered for ease of inter-
face complexity and applications where the dynamic perfor-
mance can be compromised. The series resistor RS, along
with the shunt capacitance, provide the means to adjust the
bandwidth and optimize the performance towards good
signal-to-noise ratio. In addition, the amplifier configuration
can be easily modified for an anti-aliasing filter based on a
2nd-order Sallen-Key or Multiple-Feedback topology.
The interface example, shown in Figure 4, operates with the
full-scale range of the ADS2806 set to 2Vp-p, leaving
sufficient headroom for the output of the OPA642 to drive
the converter and maintain low signal distortion.
+5V
VIN
OPA642
5V
RF
402
RG
402
RS
16.5
0.1µF
68pF
IN
1.82k
CM
IN
0.1µF
One Channel of Two
1/2
ADS2806Y
FIGURE 4. AC-Coupling the Dual-Supply Amplifier OPA642 to the ADS2806 for a 2Vp-p Full-Scale Input Range.
12 ADS2806
www.ti.com
SBAS178B

12 Page





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