Datasheet

AD9515 Data Sheet
Rev. A | Page 18 of 28
FUNCTIONAL DESCRIPTION
OVERALL
The AD9515 provides for the distribution of its input clock on
one or both of its outputs. OUT0 is an LVPECL output. OUT1
can be set to either LVDS or CMOS logic levels. Each output
has its own divider that can be set for a divide ratio selected
from a list of integer values from 1 (bypassed) to 32.
OUT1 includes an analog delay block that can be set to add an
additional delay of 1.5 ns, 5 ns, or 10 ns full scale, each with
16 levels of fine adjustment.
CLK, CLKB—DIFFERENTIAL CLOCK INPUT
The CLK and CLKB pins are differential clock input pins.
This input works up to 1600 MHz. The jitter performance is
degraded by a slew rate below 1 V/ns. The input level should be
between approximately 150 mV p-p to no more than 2 V p-p.
Anything greater can result in turning on the protection diodes
on the input pins.
See Figure 23 for the CLK equivalent input circuit. This
input is fully differential and self-biased. The signal should be
ac-coupled using capacitors. If a single-ended input must be
used, this can be accommodated by ac coupling to one side of
the differential input only. The other side of the input should be
bypassed to a quiet ac ground by a capacitor.
2.5k
5k
5k
2.5k
CLKB
CLK
V
S
CLOCK INPUT
STAGE
05597-021
Figure 23. Clock Input Equivalent Circuit
SYNCHRONIZATION
Power-On SYNC
A power-on sync (POS) is issued when the V
S
power supply is
turned on to ensure that the outputs start in synchronization.
The power-on sync works only if the V
S
power supply transi-
tions the region from 2.2 V to 3.1 V within 35 ms. The POS can
occur up to 65 ms after V
S
crosses 2.2 V. Only outputs which are
not divide = 1 are synchronized.
CLK
OUT
0V
3.3V
2.2V
3.1V
V
S
CLOCK FREQUENCY
IS EXAMPLE ONLY
DIVIDE = 2
PHASE = 0
< 65ms
INTERNAL SYNC NODE
35ms
MAX
05597-094
Figure 24. Power-On Sync Timing
SYNCB
If the setup configuration of the AD9515 is changed during
operation, the outputs can become unsynchronized. The
outputs can be re-synchronized to each other at any time.
Synchronization occurs when the SYNCB pin is pulled low and
released. The clock outputs (except where divide = 1) are forced
into a fixed state (determined by the divide and phase settings)
and held there in a static condition, until the SYNCB pin is
returned to high. Upon release of the SYNCB pin, after four
cycles of the clock signal at CLK, all outputs continue clocking
in synchronicity (except where divide = 1).
When divide = 1 for an output, that output is not affected by
SYNCB.
CLK
S
YNCB
OUT
3 CLK CYCLES 4 CLK CYCLES
EXAMPLE: DIVIDE  8
PHASE = 0
EXAMPLE DIVIDE
RATIO PHASE = 0
05597-093
Figure 25. SYNCB Timing with Clock Present
4 CLK CYCLES
CLK
OUT
SYNCB
DEPENDS ON PREVIOUS STATE AND DIVIDE RATIO
§§§
§
DEPENDS ON PREVIOUS STATE
EXAMPLE DIVIDE
RATIO PHASE = 0
MIN 5ns
05597-092
Figure 26. SYNCB Timing with No Clock Present
The outputs of the AD9515 can be synchronized by using the
SYNCB pin. Synchronization aligns the phases of the clock
outputs, respecting any phase offset that has been set on an
output’s divider.
SYNCB
05597-022
Figure 27. SYNCB Equivalent Input Circuit