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5
the transistor level is not required. Later on in the design process, models
can be replaced by more detailed descriptions. The interface of the blocks
will not be changed in this procedure. Only the description of their working
mechanisms will become more complicated. That means we have to use pin-
compatible models from the beginning.
5.3.1
Mathematical models of basic blocks
The behavior of a PLL can be illustrated using a simple description.
Instead of circuit models of the basic building blocks we use behavioral
descriptions of
Signal source described by a series connection of a voltage source and a
voltage-controlled oscillator
Phase detector realized by a multiplier
Ideal first order lowpass filter
Voltage controlled oscillator
The output of the signal source is a frequency-modulated signal.
Demodulation is carried out by the PLL [PeD91], [Kam92]. Figure 5-2
represents the schematic of the PLL.
VCO
PD
TP
VCO
N_IN
FM
PD_OUT
OUT_PLL
VCO_OUT
UUT2
UUT3
UUT4
UUT5
Figure 5-2. PLL circuit
The blocks may be realized by ideal voltage-controlled voltage sources.
Parameters of the models are introduced in the following. The FM input
signal is demodulated by the PLL. The output voltage should follow the
input voltage.
Summary :
Instead of circuit models of the basic building blocks we use behavioral descriptions of Signal source described by a series connection of a voltage source and a voltage-controlled oscillator Phase detector realized by a multiplier Ideal first order lowpass filter Voltage controlled oscillator The output of the signal source is a frequency-modulated signal.
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oltage,models,pll,signal,blocks,source,oscillator,input,figure,basic,output,realized,circuit