
Data Sheet
AD9613
Rev. C | Page 25 of 36
AD8376
AD9613
1H
1nF
VPOS
VCM
15pF
68nH
2.5k║2pF
301
165
5.1pF
3.9pF
180nH
1000pF
NOTES
1. ALL INDUCTORS ARE COILCRAFT 0603CS COMPONENTS
WITH THE EXCEPTION OF THE 1H CHOKE INDUCTORS (0603LS).
2. FILTER VALUES SHOWN FOR A 20MHz BANDWIDTH FILTER
CENTERED AT 140MHz.
180nH
220nH
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054
Figure 50. Differential Input Configuration Using the AD8376 (Filter Values Shown for a 20 MHz Bandwidth Filter Centered at 140 MHz)
VOLTAGE REFERENCE
A stable and accurate voltage reference is built into the AD9613.
The full-scale input range can be adjusted by varying the reference
voltage via SPI. The input span of the ADC tracks reference
voltage changes linearly.
CLOCK INPUT CONSIDERATIONS
For optimum performance, the AD9613 sample clock inputs,
CLK+ and CLK, should be clocked with a differential signal. The
signal is typically ac-coupled into the CLK+ and CLK pins via
a transformer or via capacitors. These pins are biased internally
floated, the CLK pin is pulled low to prevent spurious clocking.
09637-
055
AVDD
CLK+
4pF
CLK–
0.9V
Figure 51. Simplified Equivalent Clock Input Circuit
Clock Input Options
The AD9613 has a very flexible clock input structure. Clock
input can be a CMOS, LVDS, LVPECL, or sine wave signal.
Regardless of the type of signal being used, clock source jitter
section.
the AD9613 (at clock rates of up to 625 MHz). A low jitter clock
source is converted from a single-ended signal to a differential
signal using an RF balun or RF transformer.
The RF balun configuration is recommended for clock frequencies
between 125 MHz and 625 MHz, and the RF transformer is
recommended for clock frequencies from 10 MHz to 200 MHz.
The back-to-back Schottky diodes across the transformer secondary
limit clock excursions into the AD9613 to approximately 0.8 V p-p
differential. This limit helps prevent the large voltage swings of
the clock from feeding through to other portions of the AD9613,
while preserving the fast rise and fall times of the signal, which are
critical to low jitter performance.
390pF
SCHOTTKY
DIODES: HSMS2822
CLOCK
INPUT
50
100
CLK–
CLK+
ADC
Mini-Circuits
ADT1-1WT, 1:1Z
XFMR
09637-
056
Figure 52. Transformer Coupled Differential Clock (Up to 200 MHz)
390pF
25
390pF
CLOCK
INPUT
CLK–
CLK+
SCHOTTKY
DIODES:
HSMS2822
ADC
09637-
057
Figure 53. Balun-Coupled Differential Clock (Up to 625 MHz)
If a low jitter clock source is not available, another option is to
ac-couple a differential PECL signal to the sample clock input
ADCLK925 clock drivers offer excellent jitter performance.
100
0.1F
240
PECL DRIVER
50k
CLK–
CLK+
CLOCK
INPUT
CLOCK
INPUT
AD95xx
ADC
09637-
058
Figure 54. Differential PECL Sample Clock (Up to 625 MHz)