AD9260 Analog Devices, AD9260 Datasheet - Page 35

• Manufacturer Part Number: AD9260
• Description: 16-Bit High Speed Oversampled A/D Converter
• Manufacturer: Analog Devices

Specifications of AD9260

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 2.5MSPS
• Interface: Par
• Analog Input Type: Diff-Uni
• Ain Range: 4 V p-p
• Adc Architecture: Sigma-Delta
• Pkg Type: QFP

the AD9260 is referenced DVDD while the output drivers are
referenced to DRVDD. Also note that the SNR performance
of the AD9260 remains independent of the digital or driver
supply setting.
The decoupling shown in Figure 75, a 0.1 µF ceramic chip
capacitor, is appropriate for a reasonable capacitive load on the
digital outputs (typically 20 pF on each pin). Applications
involving greater digital loads should consider increasing the
digital decoupling proportionally, and/or using external
buffers/latches.
A complete decoupling scheme will also include large tantalum
or electrolytic capacitors on the PCB to reduce low frequency
ripple to negligible levels. Refer to the AD9260/EB schematic
and layouts in Figure 80 to Figure 84 for more information
regarding the placement of decoupling capacitors.
An alternative layout and decoupling scheme is shown in Figure
76. This layout and decoupling scheme is well suited for
applications in which multiple AD9260s are located on the
same PC board and/or the AD9260 is part of a multicard
mixed-signal system in which grounds are tied back at the
system supplies (i.e., star ground configuration). In this case,
the AD9260 is treated as an analog component in which its
analog (i.e., AVDD) and digital (DVDD and DRVDD) supplies
are derived from the systems +5 V analog supply and all of the
AD9260’s ground pins are tied directly to the analog ground
plane which resides directly underneath the IC.
Referring to Figure 76, each supply pin is directly decoupled to
their respective ground pin or analog ground plane via a
ceramic 0.1 µF chip capacitor. Surface mount ferrite beads are
used to isolate the analog (AVDD), digital (DVDD), and driver
0.1µF
Figure 75. Digital Supply Decoupling
3
1
DVDD
DVSS
AD9260
DRVDD
DRVSS
6
5
0.1µF
Rev. C | Page 35 of 44
supplies (DRVDD) of the AD9260 from the +5 V power bus.
Properly selected ferrite beads can provide more than 40 dB of
isolation from high frequency switching transients originating
from AD9260 supply pins. Further noise immunity from noise
is provided by the inherent power supply rejection of the
AD9260 as shown in Figure 70. If digital operation at 3 V is
desirable for power savings and or to provide for a 3 V digital
logic interface, a 5 V to 3 V linear regulator can be used to drive
DVDD and/or DRVDD. A more complete discussion on this
layout and decoupling scheme can be found in Chapter 7, pages
7-27 to 7-55 of the High speed Design Techniques seminar
book, which is available at:
www.analog.com/support/frames/lin_frameset.hml
V
A
10µF
INSERT 5/3 VOLT LINEAR REGULATOR
FOR 3 OR 3.3V DIGITAL OPERATION
BEAD CORE*
Figure 76. High Frequency Supply Rejection
FERRITE
0.1µF
0.1µF
0.1µF
0.1µF
DVDD
AVDD
AVSS
AVSS
AVDD
AVSS
DVSS
AVDD
AD9260
BITS 1–16,
DRVDD
DRVSS
DAV
CLK
SAMPLING CLOCK
GENERATOR
0.1µF
AD9260
BUFFER
LATCH
V
A