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AD12400KWS Fiches technique(PDF) 15 Page - Analog Devices

No de pièce AD12400KWS
Description  12-Bit 400 MSPS A/D Converter
Download  28 Pages
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Fabricant  AD [Analog Devices]
Site Internet  http://www.analog.com
Logo AD - Analog Devices

AD12400KWS Fiches technique(HTML) 15 Page - Analog Devices

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AD12400
Rev. 0 | Page 15 of 28
THEORY OF OPERATION
The AD12400 uses two high-speed, 12-bit analog-to-digital
converters (ADCs) in a time-interleaved configuration to
double the sample rate, while maintaining a high level of
dynamic range performance. The digital output of each ADC
channel is calibrated using a proprietary digital post processing
technique, Advanced Filter Bank (AFBTM), from VCorp
Technologies. AFB is implemented using a state-of-the-art Field
Programmable Gate Array (FPGA) and provides a wide
bandwidth, wide temperature match for any gain, phase, and
clock timing errors between each ADC channel.
TIME-INTERLEAVING ADCS
When two ADCs are time-interleaved, gain and/or phase
mismatches between each channel will produce an
Image Spur
at fs/2 – fAIN and an Offset Spur as shown in Figure 18. These
mismatches can be the result of any combination of device
tolerance, temperature, and frequency deviations.
.
–120
–110
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
0
0
20
40
60
80
100
120
140
160
180
200
FREQUENCY (MHz)
IMAGE SPUR
1
2
3
4
5
6
N
OFFSET SPUR
X
Figure 18. Image Spur Due to Mismatches between Two Interleaved ADCs
(No AFB Digital Post Processing)
Figure 19 displays the performance of a similar converter with
on-board, AFB post processing implemented. The –44 dBFS
image spur has been reduced to –77 dBFS and as a result, the
dynamic range of this time-interleaved ADC is no longer
limited by the channel matching.
0
20
40
60
80
100
120
140
160
180
200
FREQUENCY (MHz)
–120
–110
–100
–90
–80
–70
–60
–50
–40
–30
–20
–10
0
IMAGE SPUR
OFFSET SPUR
1
2
3
4
5
6
N
X
Figure 19. AD12400 with AFB Digital Post Processing
The relationship between image spur and channel mismatches
is captured in Table 7 for specific conditions.
Table 7. Image Spur vs. Channel Mismatch
Gain Error
(%)
Aperture Delay Error
(ps)
Image Spur
(dBc)
1
15
–40
0.25
2.7
–54
0.2
1.1
–62
0.025
0.5
–70
For a more detailed description of time-interleaving in ADCs
and a design example using the AD12400, refer to “Advanced
Digital Post-Processing Techniques Enhance Performance in
Time Interleaved ADC Systems,” published in the August, 2003
edition of Analog Dialogue. This article can be found at
http://www.analog.com/analogDialogue.


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