AD12401-360KWS Analog Devices Inc, AD12401-360KWS Datasheet - Page 18

• Manufacturer Part Number: AD12401-360KWS
• Description: IC,A/D CONVERTER,DUAL,12-BIT,MODULE
• Manufacturer: Analog Devices Inc

Specifications of AD12401-360KWS

• Number Of Bits: 12
• Sampling Rate (per Second): 360M
• Data Interface: Parallel
• Number Of Converters: 2
• Power Dissipation (max): 6.8W
• Voltage Supply Source: Analog and Digital
• Operating Temperature: 0°C ~ 60°C
• Package / Case: Module
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AD12401
THEORY OF OPERATION
The AD12401 uses two high speed, 12-bit 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 postprocessing technique, Advanced Filter
Bank (AFB). AFB is implemented using a state-of-the-art field
programmable gate array (FPGA) and provides a wide
bandwidth and 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 produce an image spur at
f
mismatches can be the result of any combination of device
tolerance, temperature, and frequency deviations.
Figure 20 shows the performance of a similar converter with
on-board AFB postprocessing 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.
S
/2 − f
Figure 19. Image Spur due to Mismatches Between Two Interleaved ADCs
AIN
–100
–110
–120
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–40
–50
–60
–70
–80
–90
and an offset spur, as shown in Figure 19. These
0
0
Figure 20. AD12401 with AFB Digital Postprocessing
0
0
20
20
X
X
(No AFB Digital Postprocessing)
40
40
5
IMAGE SPUR
IMAGE SPUR
60
60
2
2
FREQUENCY (MHz)
FREQUENCY (MHz)
5
80
80
100
100
3
3
120
120
4
OFFSET SPUR
OFFSET SPUR
140
140
4
160
160
1
1
180
180
6
6
N
200
N
200
Rev. A | Page 18 of 28
The relationship between image spur and channel mismatches
is captured in Table 10 for specific conditions.
Table 10. Image Spur vs. Channel Mismatch
Gain Error (%)
1
0.25
0.2
0.025
For a more detailed description of time-interleaving in ADCs and a
design example using the AD12401, see
Processing Techniques Enhance Performance in Time-Interleaved
ADC
the Analog Dialogue (www.analog.com/analogDialogue).
ANALOG INPUT
The AD12401 analog input is ac-coupled using a proprietary
transformer front-end circuit that provides 1 dB of gain flatness
over the first Nyquist zone and a −3 dB bandwidth of 480 MHz.
This front-end circuit provides a VSWR of 1.5 (50 Ω) over the
first Nyquist zone, and the typical full-scale input is 3.2 V p-p.
The Mini-Circuits® HELA-10 amplifier module can be used to
drive the input at these power levels.
CLOCK INPUT
The AD12401 requires a 400 MSPS ENCODE that is divided by 2
and distributed to each ADC channel, 180° out of phase from
each other. Internal ac-coupling and bias networks provide the
framework for flexible clock input requirements that include
single-ended sine wave, single-ended PECL, and differential
PECL. While the AD12401 is tested and calibrated using a
single-ended sine wave, properly designed PECL circuits that
provide fast slew rates (>1 V/ns) and minimize ringing result in
comparable dynamic range performance.
Aperture jitter and harmonic content are two major factors to
consider when designing the input clock circuit for the AD12401.
The relationship between aperture jitter and SNR can be
characterized using the following equation. The equation
assumes a full-scale, single-tone input signal.
SNR =
where:
f
t
N = ADC resolution (bits).
ε = ADCDNL (LSB).
V
−
A
JRMS
NOISErms
20
= input frequency.
log
= aperture jitter.
Systems, which was published in the August, 2003 edition of
⎡
⎢
⎢
⎢
⎣
= ADC input noise (LSB rms).
(
20
π
×
f
A
Aperture Delay Error (ps)
15
2.7
1.1
0.5
×
0
t
JRMS
)
2
+
1
1
5 .
×
⎛
⎜
⎝
1
2
+
N
Advanced Digital Post-
ε
⎞
⎟
⎠
2
+
⎛
⎜
⎜
⎝
2
Image Spur (dBc)
–40
–54
–62
–70
2
×
2
V
N
NOISErms
⎞
⎟
⎟
⎠
2
⎤
⎥
⎥
⎥
⎦