Total
Throughput Effective
Converters
(14-Bit
Multiplexed Needed for
Converter Architecture Resolution) Throughput Application
AD7865
SAR
416 kSPS
416 kSPS
8
AD7722
Sigma-Delta
220 kSPS
2.3 kSPS
16
AD9240
Pipelined
10 MSPS
10 MSPS
1
Of the three converters, only the AD9240 has the throughput
needed to convert all 16 channels. The AD7865 has sufficient
throughput for 2 inputs per converter. To use the AD7865 in this
application, 8 converters would be needed. The AD7722 would
4
Analog Dialogue 33-8 (1999)
need to be used in a converter-per-channel implementation; thus
16 converters would be required.
Summary
While not exhaustive, the following table summarizes and ranks
(in a generalized sense) the relative advantages of flash, pipelined,
SAR, and sigma-delta architectures. A rank of 1 in a performance
category indicates that the architecture is inherently better than
the others for that category. An * indicates that the architecture
has the capability or characteristic listed.
Sigma-
C
haracteristic
Flash Pipelined SAR Delta
Throughput
1
2
3
4
Resolution (ENOB)
4
3
2
1
Latency
1
3
2
4
Suitability for converting multiple
signals per ADC
1
2
1
3
Capability to convert non-periodic
multiplexed signals
1
2
1
3
Simplified anti-aliasing
*
Can undersample
*
*
*
Can increase resolution through
averaging (with dither noise)
*
*
*
ACKNOWLEDGMENT
The author is indebted to Alain Guery and Mike Coln for providing
valuable direction, and for providing the figures shown.
REFERENCES
Analog-Digital Conversion Handbook
, The Engineering Staff
of Analog Devices, Inc. Englewood Cliffs, NJ: Prentice Hall,
1986. ISBN 0-13-032848-0. Available from Analog Devices:
Phone (781) 461-3392.
Practical Analog Design Techniques
, edited by Walt Kester. Norwood,
MA: Analog Devices, Inc., 1995. ISBN 0-916550-16-8. Available
from Analog Devices: Phone (781) 461-3392. Also available free
on the Internet as
PDF chapters
. http://www.analog.com/support/
standard_linear/seminar_material/index.html
High Speed Design Techniques
, edited by Walt Kester. Norwood, MA:
Analog Devices, Inc., 1996. ISBN 0-916550-17-6. Available from
Analog Devices: Phone (781) 461-3392. Also available free on the
Internet as
PDF chapters
. http://www.analog.com/support/
standard_linear/seminar_material/index.html
Linear Design Seminar
, edited by Walt Kester. Norwood, MA:
Analog Devices, Inc., 1995. ISBN 0-916550-15-X. Available from
Analog Devices: Phone (781) 461-3392.
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