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Data Sheet

AD9545

Rev. A | Page 47 of 157

REFERENCE DEMODULATOR

REFERENCE DEMODULATOR OVERVIEW

The AD9545 has four reference demodulators, one for each

reference input, REFA, REFAA, REFB, and REFBB. When

enabled, the demodulators extract embedded modulation

events from their associated input carrier clock signal. These

modulation events are essentially phase variations appearing on

the falling edge of certain input clock cycles. The primary intent

of the demodulators is to enable the detection of an embedded

clock signal originating from the output distribution of another

AD9545 (see the Distribution Embedded Output Clock

Modulation section for more detail on embedded clock

modulation).

Figure 45 shows a basic block diagram of the reference

demodulator. Although Figure 45 specifically shows the

demodulator associated with the REFA input, the diagram

applies similarly to the REFAA, REFB, and REFBB inputs. A

reference input configured for differential operation only has

access to one demodulator: Demodulator A for the REFA and

REFAA differential input and Demodulator B for the REFB and

REFBB differential input (see Figure 1).

The input clock signal at a REFx input (where x is A, AA, B, or

BB) passes through the reference receiver and drives the clock

input of the reference divider, the normal signal path when the

REFx input signal does not carry an embedded clock signal.

The output of the receiver also drives the demodulator input.

When enabled, the demodulator extracts the embedded clock

signal and uses it to synchronize the reference divider.

The demodulator expects a reference input signal containing

modulation events as described in the Distribution Embedded

Output Clock Modulation section. In general, the modulation

constitutes a lower frequency clock signal embedded within the

higher frequency carrier. The demodulator extracts the

embedded clock and the polarity of the modulation events

(optional).

The demodulated clock signal is available to the user via a

suitably configured Mx pin.

Seven control functions are associated with each demodulator

accessible via the register map, as follows:

•

Enable

•

Delay

•

Sensitivity

•

Polarity

•

Auto polarity detection

•

Persistence

•

Bandwidth

DEMODULATOR ENABLE

To enable the demodulator use the enable REFx demodulator

bit (where x is A, AA, B, or BB) in Bit D3 of Register 0x0302 to

0 (default) disables the demodulator, while Logic 1 enables it.

Note the demodulator requires at least an 8:1 ratio between the

frequency of the reference input and the frequency of the

embedded modulation events.

POLARITY

REFERENCE

RECEIVER

SENSITIVITY

ENABLE REFA DEMODULATOR PERSIST

ENABLE REFA DEMODULATOR POLARITY

REFA DEMODULATOR SYNC EDGE

ENABLE REFA DEMODULATOR

REFA DEMODULATOR EVENT POLARITY

REFA DEMODULATOR SENSITIVITY

REFA/AA DEMODULATOR BAND SELECT

BANDWIDTH

DEMODULATOR

DEMOD OUT

DEMOD IN

SYNC

AUTO POLARITY DETECT

DEMODULATOR A

POLARITY OUT

PERSISTENCE

REFERENCE

DIVIDER

REFA

ENABLE

SYNC

REFA

TDC

TEXT

= BIT(S) IN THE REGISTER MAP

Figure 45. Reference Demodulator

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