Product Specification
PE97022
Page 9 of 14
Document No. 70-0235-04 │ www.psemi.com
©2007-2008 Peregrine Semiconductor Corp. All rights reserved.
Main Counter Chain
Normal Operating Mode
The main counter chain divides the RF input
frequency, F
in
, by an integer derived from the
user-defined values in the “M” and “A” counters. It
is composed of the 10/11 dual modulus prescaler,
modulus select logic, and 9-bit M counter. Setting
Pre_en “low” enables the 10/11 prescaler. Setting
Pre_en “high” allows F
in
to bypass the prescaler
and powers down the prescaler.
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 x (M + 1) + A] (1)
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 x (M + 1) + A] x (f
r
/ (R+1)) (2)
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 x (f
r
/ (R+1)) to
obtain contiguous channels. Programming the M
Counter with the minimum value of “1” will result in
a minimum M Counter divide ratio of “2”.
In Direct Interface Mode, main counter inputs M
7
and M
8
are internally forced low. In this mode, the
M value is limited to 1 ≤ M ≤
127.
Prescaler Bypass Mode
Setting Pre_en “high” allows F
in
to bypass and
power down the prescaler. In this mode, the
10/11 prescaler and A register are not active, 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) x (f
r
/ (R+1)) ) (3)
where 1 ≤ M ≤ 511
In Direct Interface Mode, main counter inputs M
7
and M
8
are internally forced low. In this mode, the
M value is limited to 1 ≤ M ≤
127.
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) (4)
where 0 ≤ R ≤ 63
Note that programming R with “0” will pass the
reference frequency, f
r
, directly to the phase
detector.
In Direct Interface Mode, R Counter inputs R
4
and R
5
are internally forced low (“0”). In this
mode, the R value is limited to 0 ≤ R ≤ 15.
Register Programming
Parallel Interface Mode
Parallel Interface Mode is selected by setting the
Bmode input “low” and the Smode input “low”.
Parallel input data, D[7:0], are latched in a
parallel fashion into one of three 8-bit primary
register sections on the rising edge of M1_WR,
M2_WR, or A_WR per the mapping shown in
Table 7 on page 10. The contents of the
primary register are transferred into a secondary
register on the rising edge of Hop_WR
according to the timing diagram shown in Figure
7. Data is transferred to the counters as shown
in Table 7 on page 10.
The secondary register acts as a buffer to allow
rapid changes to the VCO frequency. This
double buffering for “ping-pong” counter control
is programmed via the FSELP input. When
FSELP is “high”, the primary register contents
set the counter inputs. When FSELP is “low”,
the secondary register contents are utilized.
Parallel input data, D[7:0], are latched into the
enhancement register on the rising edge of
E_WR according to the timing diagram shown in
Figure 6. This data provides control bits as
shown in Table 8 on page 10 with bit
functionality enabled by asserting the Enh input
“low”.
