AD9289 Analog Devices, AD9289 Datasheet - Page 19

• Manufacturer Part Number: AD9289
• Description: Quad 8-Bit, 65 MSPS, Serial LVDS A/D Converter
• Manufacturer: Analog Devices

Specifications of AD9289

• Resolution (bits): 8bit
• # Chan: 4
• Sample Rate: 65MSPS
• Interface: Ser
• Analog Input Type: Diff-Uni
• Ain Range: 1 V p-p,2 V p-p
• Adc Architecture: Pipelined
• Pkg Type: CSP

External Reference Operation
The use of an external reference may be necessary to enhance
the gain accuracy of the ADC or improve thermal drift
characteristics. Figure 36 shows the typical drift characteristics
of the internal shared reference in both 1 V and 0.5 V modes.
–0.05
–0.10
–0.15
–0.20
–0.25
0.15
0.10
0.05
0
–40
–20
Figure 36. Typical VREF Drift
0
TEMPERATURE (°C)
20
40
V
REF
= 0.5V
V
60
REF
= 1.0V
80
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When the SENSE pin is tied to AVDD, the internal reference is
disabled, allowing the use of an external reference. An internal
reference buffer loads the external reference with an equivalent
7 kΩ load. The internal buffer still generates the positive and
negative full-scale references, REFT_A and REFT_B and
REFB_A and REFB_B , for the ADC core. The input span is
always twice the value of the reference voltage; therefore, the
external reference must be limited to a maximum of 1 V.
Power and Ground Recommendations
When connecting power to the AD9289, it is recommended that
two separate 3.0 V supplies be used. One for analog (AVDD)
and one for digital (DRVDD). If only one supply is available
then it should be routed to the AVDD first and tapped off and
isolated with a ferrite bead or filter choke with decoupling
capacitors proceeding. One may want to use several different
decoupling capacitors to cover both high and low frequencies.
These should be located close the point of entry at the pc board
level as well as close to the parts with minimal trace length.
A single pc board ground plane should be sufficient when using
the AD9289. With proper decoupling and smart partitioning of
the pc board’s analog, digital, and clock sections, optimum
performance is easily achieved.
AD9289