48 Chapter
5
branch. The branch current is zero. The second input branch is declared in
the same way. The third quantity statement presents the output voltage
source branch. It connects the terminal OUTP and the electrical reference
node. The branch voltage is VOUT and the branch current IOUT. The value
of the branch current depends on the interconnection of the phase detector
with other models. The relationship that has to be fulfilled by the branch
voltages and currents is given by the simultaneous statement
VOUT ==
GAIN*VIN1*VIN2;
Thus, the VHDL-AMS model represents the mathematical
model description given in Section 5.3.1.
Voltage controlled oscillator
INP
OUTP
VIN VOUT
Figure 5-5.
Structure of the basic VCO model
The VCO model is written in a similar way to the phase detector. The
entity declaration was already shown in Section 5.3.2. The architecture
contains an additional declaration for PHI that is neither a branch current nor
a branch voltage. Furthermore the initial condition is considered during
operating point analysis (DOMAIN equals QUIESCENT_DOMAIN).
PHI'DOT is the time derivative of PHI. The SIN function and the
mathematical constants can be found in the package MATH_REAL that is
introduced with the first two lines of the following code:
library IEEE;
use IEEE.MATH_REAL.all;
architecture BASIC of VCO is
quantity VIN
across INP; -- open input branch
quantity VOUT across IOUT through OUTP; -- output branch
quantity PHI : REAL; -- free quantity PHI
begin
if DOMAIN = QUIESCENT_DOMAIN use
PHI == PHI0; -- initial condition
else
PHI'DOT == MATH_2_PI*(KF*VIN + F0); -- see VCO description
end use;
VOUT == AMPL*SIN(PHI); -- see VCO description
end architecture BASIC;
Summary :
48 Chapter 5 branch. The branch voltage is VOUT and the branch current IOUT. The relationship that has to be fulfilled by the branch voltages and currents is given by the simultaneous statement VOUT == GAIN*VIN1*VIN2; The architecture contains an additional declaration for PHI that is neither a branch current nor a branch voltage.
Tags :
out,quantity,phi,current,model,oltage,outp,basic,description,use,architecture,domain,condition