ADC16DV160
SNAS488H –AUGUST 2009–REVISED FEBRUARY 2013
www.ti.com
Even though LVDS outputs reduce ground bounce, the positive and negative signal path have to be well
matched, and their traces should be kept as short as possible. It is recommend to place an LVDS repeater
between the ADC16DV160 and digital data receiver block to prevent coupling noise from the receiving block
when the length of the traces are long or the noise level of the receiving block is high.
Capacitive coupling between the typically noisy digital circuitry and the sensitive analog circuitry can lead to poor
performance. The solution is to keep the analog circuitry separated from the digital circuitry, and to keep the
clock line as short as possible.
Since digital switching transients are composed largely of high frequency components, total ground plane copper
weight will have little effect upon the logic-generated noise. Because of the skin effect, the total surface area is
more important than its thickness.
Generally, analog and digital lines should not cross. However whenever it is inevitable, make sure that these
lines are crossing each other at 90° to minimize cross talk. Digital output and output clock signals must be
separated from analog input, references and clock signals unconditionally to ensure the maximum performance
from the ADC16DV160. Any coupling may result in degraded SNR and SFDR performance especially for high IF
applications.
Be especially careful with the layout of inductors and transformers. Mutual inductance can change the
characteristics of the circuit in which they are used. Inductors and transformers should not be placed side by
side, even with just a small part of their bodies beside each other. For instance, place transformers for the analog
input and the clock input at 90° to one another to avoid magnetic coupling. It is recommended to place the
transformers of the input signal path on the top side, and the transformer for the clock signal path on the bottom
side. Every critical analog signal path like analog inputs and clock inputs must be treated as a transmission line
and should have a solid ground return path with a small loop area.
The analog input should be isolated from noisy signal traces to avoid coupling of spurious signals into the input.
Any external component (e.g., a filter capacitor) connected between the converter’s input pins and ground or to
the reference pins and ground should be connected to a very clean point in the ground plane.
All analog circuitry (input amplifiers, filters, reference components, etc.) should be placed in the analog area of
the board. All digital circuitry and dynamic I/O lines should be placed in the digital area of the board. The
ADC16DV160 should be between these two areas. Furthermore, all components in the reference circuitry and
the input signal chain that are connected to ground should be connected together with short traces and enter the
ground plane at a single, quiet point. All ground connections should have a low inductance path to ground.
The ground return current path can be well managed when the supply current path is precisely controlled and the
ground layer is continuous and placed next to the supply layer. This is because of the proximity effect. A ground
return current path with a large loop area will cause electro-magnetic coupling and results in poor noise
performance. Note that even if there is a large plane for a current path, the high-frequency return current path is
not spread evenly over the large plane, but only takes the path with lowest impedance. Instead of a large plane,
using a thick trace for supplies makes it easy to control the return current path. It is recommended to place the
supply next to the GND layer with a thin dielectric for a smaller ground return loop. Proper location and size of
decoupling capacitors provides a short and clean return current path.
SUPPLIES AND THEIR SEQUENCE
There are three supplies for the ADC16DV160: one 3.0V supply VA3.0 and two 1.8V supplies VA1.8 and VDR. It is
recommended to separate VDR from VA1.8 supplies, any coupling from VDR to the rest of the supplies and analog
signals could cause lower SFDR and noise performance. When VA1.8 and VDR are both from the same supply
source, coupling noise can be mitigated by adding a ferrite-bead on the VDR supply path.
Different decoupling capacitors can be used to provide current over wide frequency range. The decoupling
capacitors should be located close to the point of entry and close to the supply pins with minimal trace length. A
single ground plane is recommended because separating ground under the ADC16DV160 could cause an
unexpected long return current path.
The VA3.0 supply must turn on before VA1.8 and/or VDR reaches a diode turn-on voltage level. If this supply
sequence is reversed, an excessive amount of current will flow through the VA3.0 supply. The ramp rate of the
VA3.0 supply must be kept less than 60 V/mS (i.e., 60 μS for 3.0V supply) in order to prevent excessive surge
current through ESD protection devices.
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