PE97632DIE Datasheet, PDF (9/16 Pages) Peregrine Semiconductor – 3.5 GHz Delta-Sigma Modulated Fractional-N Frequency Synthesizer for Low Phase Noise Applications

PE97632 DIE
Product Specification
Main Counter Chain
Normal Operating Mode
Setting the Pre_en control bit “low” enables the
÷10/11 prescaler. The main counter chain then
divides the RF input frequency (F_IN) by an integer
or fractional number derived from the values in the
“M” and “A” counters and the DSM input word K.
The accumulator size is 18 bit, so the fractional
value is fixed from the ratio K/2¹⁸. There is an
additional bit in the DSM that acts like an extra bit
(19^th bit). This bit is enabled by asserting the pin
RAND_SEL to “high”. Enabling this bit has the
benefit of reducing the spurious levels. However,
a small frequency offset will occur. This positive
frequency offset is calculated with the following
equation.
f_offset = [F_R / (R+1)] / 2¹⁹
(1)
All of the following equations do not take into
account this frequency offset. If this offset is
important to a specific frequency plan, appropriate
account needs to be taken.
In the normal mode, the output from the main
counter chain (f_p) is related to the VCO frequency
(F_IN) by the following equation:
f_P = F_IN / [10 × (M+1) + A + K/2¹⁸]
(2)
where A ≤ M + 1, 1 ≤ M ≤ 511
When the loop is locked, F_IN is related to the
reference frequency (F_R) by the following
equation:
F_IN = [10 × (M+1) + A + K/2¹⁸] × [F_R / (R+1)] (3)
where A ≤ M + 1, 1 ≤ M ≤ 511
A consequence of the upper limit on A is that F_IN
must be greater than or equal to 90 × [F_R / (R+1)]
to obtain contiguous channels. The A counter can
accept values as high as 15, but in typical
operation it will cycle from 0 to 9 between
increments in M.
Programming the M counter with the minimum
allowed value of “1” will result in a minimum M
counter divide ratio of “2”.
Document No. DOC-01626-3 │ www.psemi.com
Prescaler Bypass Mode (*)
Setting the frequency control register bit Pre_en
“high” allows F_IN to bypass the ÷10/11 prescaler.
In this mode, the prescaler and A counter are
powered down, and the input VCO frequency is
divided by the M counter directly. The following
equation relates F_IN to the reference frequency F_R:
F_IN = (M+1) × [F_R / (R+1)]
(4)
where 1 ≤ M ≤ 511
(*) Only integer mode
In frequency bypass mode, neither A counter or K
counter is used. Therefore, only integer-N
operation is possible.
Reference Counter
The reference counter chain divides the reference
frequency, F_R, down to the phase detector
comparison frequency, f_c.
The output frequency of the 6-bit R counter is
related to the reference frequency by the following
equation:
f_c = F_R / (R+1)
(5)
where 0 ≤ R ≤ 63
Note that programming R with “0” will pass the
reference frequency, F_R, directly to the phase
detector.
Register Programming
Serial Interface Mode
While the E_WR input is “low” and the S_WR
input is “low”, serial input data (SDATA input), B₀
to B₂₀, are clocked serially into the primary register
on the rising edge of SCLK, MSB (B₀) first. The
LSB is used as address bit. When “0”, the
contents from the primary register are transferred
into the secondary register on the rising edge of
either S_WR according to the timing diagrams
shown in Figure 4. When “1”, data is transferred to
the auxiliary register according to the same timing
diagram. The secondary register is used to
program the various counters, while the auxiliary
register is used to program the DSM.
Data are transferred to the counters as shown in
Table 8.
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