AD9230-250EB Analog Devices, Inc., AD9230-250EB Datasheet - Page 15

• Manufacturer Part Number: AD9230-250EB
• Description: 12-bit, 170/210/250 Msps 1.8 V A/d Converter
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
Figure 16. Single-Ended Input Configuration using SPI enabled CML function
CLOCK INPUT CONSIDERATIONS
For optimum performance, the AD9230 the sample clock inputs
(CLK+ and CLK-) should be clocked with a differential signal.
This signal is typically ac-coupled into the CLK+ and CLK- pins
via a transformer or capacitors. These pins are biased internally
and require no additional bias (See Figure X).
Figure X shows one preferred method for clocking the AD9230.
The clock source (low jitter) is converted from single-ended to
differential using an RF transformer. The back-to-back Schottky
diodes across the transformer secondary limit clock excursions
into the AD9230 to approximately 0.8 V p-p differential. This
helps prevent the large voltage swings of the clock from feeding
through to other portions of the AD9230 while preserving the
fast rise and fall times of the signal, which are critical to a low
jitter performance.
If a low jitter clock is available, another option is to ac-couple a
differential PECL signal to the sample clock input pins as shown
in Figure X. The AD9512 (or same family) from offers excellent
jitter performance.
CLK+
1.25Vp-p
2pF
Source
Clock
Figure X. Transformer Coupled Differential Clock
Figure .Equivalent Clock Input Circuit
4 9 . 9
:
1 0 µ F
0 . 1 µ F
AVDD
1.2V
R
0.1uF
CLK+
CLK-
CML
VIN+
VIN-
A D9 230
AVDD
AGND
AD9230
2pF
CLK-
Rev. PrE | Page 15 of 21
PECL
AD9512
Figure X. Differential PECL Sample Clock
150:
150:
0.1uF
0.1uF
CLK+
CLK-
AD9230
AD9230