PS2500 2.2 GHz Fractional-N Frequency Synthesizer
- 6 -
Philsar Semiconductor Inc.
146 Colonnade Road S.
Nepean, Ontario, Canada
K2E 7Y1
Tel: 613-274-0922
Fax: 613-274-0915
www.philsar.com
PMP-001-DS2 V1.2
Synthesizer Register Programming
In the following equations,
Fractional-N Applications
The desired division ratio for the Main and Auxiliary Synthesizer is given by:
Nfractional = FVCO / Fdiv_ref
where Nfractional must be between 37.5 and 537.5 for the auxiliary.
The value to be programmed in the Main or Auxiliary Divider Register is given by:
Nreg = Round
1 [N
fractional] - 32
When in fractional mode, allowed values for Nreg are from 6 to 505 inclusive.
The value to be programmed in the Main or Auxiliary Dividend Register(s) is given by:
dividend = Round [divider x (Nfractional - Nreg - 32)]
where the divider is either 1024 in 10-bit mode or 262144 in 18-bit mode. Therefore, the dividend is a
signed binary value either 10 or 18 bits long.
Nfractional
Desired VCO division ratio in fractional-N applications. This number is a real number
and can be interpreted as the reference frequency (Fref) multiplying factor such that
the resulting frequency is equal to the desired VCO frequency.
Ninteger
Desired VCO division ratio in integer-N applications. This number is an integer and
can be interpreted as the reference frequency (Fref) multiplying factor such that the
resulting frequency is equal to the desired VCO frequency.
Nreg
9-bit unsigned input value to the divider ranging from 0 to 511(Integer-N mode) and
from 6 to 505 (Fractional-N mode)
divider
262144 when the
∆Σ modulator is in 18-bit mode, 1024 when the ∆Σ is in 10-bit
mode
dividend
When in 18-bit mode, 18-bit signed input value to the
∆Σ modulator, ranging from
-131072 to +131071 providing 262144 steps, each of Fdiv_ref / 2
18 (Hz).
or
when in 10-bit mode, 10-bit signed input value to the
∆Σ modulator, ranging from
-512 to +511 providing 1024 steps, each of Fdiv_ref / 2
10 Hz.
FVCO
Desired VCO frequency (either Fvco_main or Fvco_aux).
Fdiv_ref
Divided reference frequency presented to the phase detector (either Fref_main or
Fref_aux).
1.
Where the Round function rounds the number to the nearest integer.
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