![](http://datasheet.mmic.net.cn/Intersil/ISLA222P13IRZ_datasheet_101393/ISLA222P13IRZ_31.png)
ISLA222P
31
FN7853.1
June 17, 2011
A/D Evaluation Platform
Intersil offers an A/D Evaluation platform which can be used to
evaluate any of Intersil’s high speed A/D products. The platform
consists of a FPGA based data capture motherboard and a family
of A/D daughtercards. This USB based platform allows a user to
quickly evaluate the A/D’s performance at a user’s specific
application frequency requirements. More information is
available at
Layout Considerations
Split Ground and Power Planes
Data converters operating at high sampling frequencies require
extra care in PC board layout. Many complex board designs
benefit from isolating the analog and digital sections. Analog
supply and ground planes should be laid out under signal and
clock inputs. Locate the digital planes under outputs and logic
pins. Grounds should be joined under the chip.
Clock Input Considerations
Use matched transmission lines to the transformer inputs for the
analog input and clock signals. Locate transformers and
terminations as close to the chip as possible.
Exposed Paddle
The exposed paddle must be electrically connected to analog
ground (AVSS) and should be connected to a large copper plane
using numerous vias for optimal thermal performance.
Bypass and Filtering
Bulk capacitors should have low equivalent series resistance.
Tantalum is a good choice. For best performance, keep ceramic
bypass capacitors very close to device pins. Longer traces will
increase inductance, resulting in diminished dynamic
performance and accuracy. Make sure that connections to
ground are direct and low impedance. Avoid forming ground
loops.
LVDS Outputs
Output traces and connections must be designed for 50
Ω (100Ω
differential) characteristic impedance. Keep traces direct and
minimize bends where possible. Avoid crossing ground and
power-plane breaks with signal traces.
LVCMOS Outputs
Output traces and connections must be designed for 50
Ω
characteristic impedance.
Unused Inputs
Standard logic inputs (RESETN, CSB, SCLK, SDIO and SDO) which
will not be operated do not require connection to ensure optimal
A/D performance. These inputs can be left floating if they are not
used. Tri-level inputs (NAPSLP) accept a floating input as a valid
state, and therefore should be biased according to the desired
functionality.
Definitions
Analog Input Bandwidth is the analog input frequency at which
the spectral output power at the fundamental frequency (as
determined by FFT analysis) is reduced by 3dB from its full-scale
low-frequency value. This is also referred to as Full Power
Bandwidth.
Aperture Delay or Sampling Delay is the time required after the
rise of the clock input for the sampling switch to open, at which
time the signal is held for conversion.
Aperture Jitter is the RMS variation in aperture delay for a set of
samples.
Clock Duty Cycle is the ratio of the time the clock wave is at logic
high to the total time of one clock period.
Differential Non-Linearity (DNL) is the deviation of any code width
from an ideal 1 LSB step.
FIGURE 49. VCM_OUT OUTPUT
Equivalent Circuits (Continued)
VCM
AVDD
0.94V
+
–