ADF4112BRUZ-REEL View Datasheet(PDF) - Analog Devices

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ADF4112BRUZ-REEL

RF PLL Frequency Synthesizers

Analog Devices 

RESYNCHRONIZING THE PRESCALER OUTPUT

Table 7 (the Reference Counter Latch Map) shows two bits,

DB22 and DB21, which are labeled DLY and SYNC, respectively.

These bits affect the operation of the prescaler.

With SYNC = 1, the prescaler output is resynchronized with the

RF input. This has the effect of reducing jitter due to the

prescaler and can lead to an overall improvement in synthesizer

phase noise performance. Typically, a 1 dB to 2 dB improvement

is seen in the ADF4113. The lower bandwidth devices can show

an even greater improvement. For example, the ADF4110 phase

noise is typically improved by 3 dB when SYNC is enabled.

With DLY = 1, the prescaler output is resynchronized with a

delayed version of the RF input.

ADF4110/ADF4111/ADF4112/ADF4113

If the SYNC feature is used on the synthesizer, some care must

be taken. At some point, (at certain temperatures and output

frequencies), the delay through the prescaler coincides with the

active edge on RF input; this causes the SYNC feature to break

down. It is important to be aware of this when using the SYNC

feature. Adding a delay to the RF signal, by programming

DLY = 1, extends the operating frequency and temperature

somewhat. Using the SYNC feature also increases the value of

the AIDD for the device. With a 900 MHz output, the ADF4113

AIDD increases by about 1.3 mA when SYNC is enabled and by

an additional 0.3 mA if DLY is enabled.

All the typical performance plots in this data sheet, except for

Figure 8, apply for DLY and SYNC = 0, i.e., no resynchroniza-

tion or delay enabled.

Rev. C | Page 21 of 28

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