AD9515SLASHPCB datasheet(18/28 Pages) AD

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AD9515

Rev. 0 | 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

CLKB

CLK

CLOCK INPUT

STAGE

Figure 23. Clock Input Equivalent Circuit

SYNCHRONIZATION

Power-On SYNC

A power-on sync (POS) is issued when the VS power supply is

turned on to ensure that the outputs start in synchronization.

The power-on sync works only if the VS 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 VS crosses 2.2 V. Only outputs which are

not divide = 1 are synchronized.

CLK

OUT

3.3V

2.2V

3.1V

CLOCK FREQUENCY

IS EXAMPLE ONLY

DIVIDE = 2

PHASE = 0

< 65ms

INTERNAL SYNC NODE

35ms

MAX

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

SYNCB

OUT

3 CLK CYCLES

4 CLK CYCLES

EXAMPLE: DIVIDE

≥ 8

PHASE = 0

EXAMPLE DIVIDE

RATIO PHASE = 0

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

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

Figure 27. SYNCB Equivalent Input Circuit

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