VHDL-AMS FOR BLOCK LEVEL SIMULATION
43
Signal Source
An independent voltage source drives the voltage controlled oscillator
UUT2. The output of the VCO is a frequency-modulated voltage. It is used
as PLL input.
Phase detector (PD)
The phase detector is realized in a simple manner. The values of the two
input waveforms are multiplied by the gain of the phase detector. Two open
input branches, which are used to measure the input voltages vin
1
and vin
2
,
and an ideal controlled voltage source that drives the output can be used to
model the phase detector:
)
(
)
(
)
(
2
1
t
vin
t
vin
gain
t
vout
Voltage controlled oscillator (VCO)
The frequency of the sinusoidal VCO output voltage depends on the
input voltage vin measured by an open branch. In our simple model we
assume that the frequency is proportional to the input voltage plus center
frequency f
0
. Considering the basic definition that the derivative of the phase
equals the product of frequency and 2 we start with
0
)
(
2
f
t
vin
kf
dt
d
and the initial condition
0
)
0
(
The output voltage results from
)
(
sin
)
(
t
Ampl
t
vout
kf is the VCO gain measured in Hz/V. Ampl is the amplitude of the
output voltage.
Lowpass filter (LP)
The lowpass filter is characterized by its cut-off frequency and gain. The
input voltage vin is measured by an open branch. It controls the voltage vout
of an ideal voltage source. The Laplace transfer function of the lowpass filter
is given by
)
(
)
(
2
1
)
(
s
vin
s
vout
f
s
gain
s
H
c
, i.e.
c
f
s
gain
s
vin
s
vout
2
1
)
(
)
(
.
Summary :
Two open input branches, which are used to measure the input voltages vin 1 and vin 2 , and an ideal controlled voltage source that drives the output can be used to model the phase detector: ) ( ) ( ) ( 2 1 t vin t vin gain t vout Voltage controlled oscillator (VCO) The frequency of the sinusoidal VCO output voltage depends on the input voltage vin measured by an open branch.
Tags :
input,gain,out,phase,output,frequency,detector,source,controlled,open,lowpass,filter,used