synthe_scicos

Scicos Diagram
fr - eng

Simple scicos diagram of an integer-N frequency synthesizer

$\epsfig{file=synthe_scicos_diagr.eps,width=400pt}$

Module

Modnum

Simple scicos diagram of an integer-N frequency synthesizer

This diagram realizes the simulation of a Type-2 integer $\div N$ frequency synthesizer with the continuous time behavior of the Scicos simulator.
A general block diagram of such a subsystem can be illustrated by the following figure.

$\begin{figure}\centering \scalebox{0.9}{% \input{synthe.pstex_t}} \end{figure}$

Figure 1: General block diagram of a $\div N$ frequency synthesizer

Type-2 $\div N$ frequency synthesizer is composed of :

a Local Oscilator (LO) which delivers a low frequency fixed output wave,
a divider $\div R$ ; frequency output of this divider is called update frequency of the Phase Frequency Detector (PFD),
a PFD, nonlinear component realized with digital flip-flops,
a Charge Pump (CP) that converts logic signals coming from PFD to analog signals,
a (low-pass) Loop Filter (LF),
a Voltage Controlled Oscillator (VCO),
a feedback divider $\div N$ .

When it is understand in linear domain, this subsystem doesn't really differs from a classical Phase Locked Loop[1] (PLL). It only adds a frequency divider $\div N$ in a feedback path to convert the high frequency coming from the VCO.

With this feedback divider, the output frequency of the synthesizer is given by :

$\begin{eqnarray} F_{\rm s} = F_{\rm ref} N \end{eqnarray}$

with :

$F_{\rm s}$ the output frequency of the VCO in steady state,
$F_{\rm ref}$ the update frequency of the PFD,
the value of the divider factor of the feedback frequency divider.

Context

//**PFD**//
F_ref = 50e6;
T_ref = 1/F_ref;
//Noise variance of LO
sig_ref=T_ref*0.1/100

//**VCO**//
Fo = 2.045e9;
To = 1 / Fo;
wo=2*%pi * Fo;
kv = 100.5e6; //local sensitivity
//coef for input nonlinear caracteristic
alpha=6.91e9;
beta2=0.15;
//white noise power
j_vco=1e6;

//**feedback divider**//
N=52;

//**output frequency**//
Fd=N*F_ref;

//**sampling clock of VCO**//
Nsampl = 4;
Tsampl = 1/(Fd*Nsampl);
Fsampl = 1 / Tsampl;

//**charge pump**//
Icp = 5e-3;
Ileak=10e-6;

//**loop filter**//
fn=F_ref/180;
phi=%pi/4;
kv=kv*2*%pi
[tau1,tau,tau2]=calcul_3eme_ordre(fn,phi,kv,Icp,N);
s=poly(0,'s');
num=1+tau1*s;
den=tau*s*(1+tau2*s);
kv=kv/(2*%pi)

//**final time simulation**//
Tfin=1000*T_ref