RMX2 Datasheet, PDF (6/12 Pages) Radiometrix Ltd – Narrow Band Direct Interface Multi Channel Transceiver

n = ^fVCO
f _comp
note:
f _comp
=
f _OSC
R
Equation 4
Also, this PLL IC operates with the following R, N, A and M relational expressions.
R = ^fOSC
f _comp
Equation 5
N = INT  ⁿ 
^M 
A = n − (M × N )
INT: Integer portion of a division
Equation 6
Equation 7
As an example, the setting value of RF channel frequency fch 434.6750MHz can be calculated as below.
Conditions:
Constant:
Constant:
Channel center frequency:
Offset frequency:
Reference frequency:
fch = 434.6750MHz
foffset=21.7 MHz
fosc=21.25 MHz
Set 25 kHz for Phase Comparison Frequency fcomp and 64 for Prescaler value M
The frequency of VCO will be:
fvco = fexpect = fch – foffset = 434.675 –21.7 = 412.975MHz
Dividing value “n” is derived from Equation 4
n = fvco / fcomp = 412.975MHz/25kHz = 16519
Value “R” of the Reference Counter is derived from Equation 5.
R = fosc/fcomp = 21.25MHz/25kHz = 850
Value “N” of the programmable counter is derived from Equation 6.
N = INT (n/M) = INT(16519/64) = 258
Value “A“ of the swallow counter is derived from Equation 7.
A = n – (M x N) = 16519 – 64 x 258 = 7
The frequency of RMX2 is locked at a centre frequency fch by inputting the PLL setting values N, A and
R obtained with the above equations as serial data. The above calculations are the same for the other
frequencies.
Method of serial data input to the PLL
After the RF channel table plan is decided, the data needs to be allocated to the ROM table and read
from there or calculated with the software.
Together with this setting data, operation bits that decide operation of the PLL must be sent to the
PLL. The operation bits for setting the PLL are as follows. These values are placed at the head of the
reference counter value and are sent to the PLL.
CS: Charge pump current select bit
CS = 0
±1.5 mA select VCO is optimised to ±1.5 mA
LDS: LD/fout output setting bit
LDS = 0
LD select
Hardware is set to LD output
FC: Phase control bit for the phase comparator
FC = 1
Hardware operates at this phase
Radiometrix Ltd
RMX2-433-10 Data sheet
Page 6/12