CHAPTER 1 - Fundamentals of Electrical Circuits
26
Figure 1.5-13 Voltage and current across the capacitor at 2GHz
Figure 1.5-12 and Figure 1.5-13 show voltage and current waveforms for the capacitor at 1GHz and 2
GHz respectively. The markers also show the maximum amplitudes of current and voltage and the
time stamps at which such amplitudes are reached. Let us start with the 1GHz case.
At 1 GHz the period of the signal is
Also,
from Figure 1.5-12 the between the two markers is
is therefore a quarter of
and
hence a quarter of a full 360ι period i.e. 90ι. The phase shift
between voltage and current is therefore 90⁰. In other words the current leads the voltage by 90⁰.
Let us now look at the relative amplitudes of voltage and current
Now
let us calculate the capacitor impedance from (1.5-6)(b)
This
last equation demonstrates that the modulus of the impedance calculated algebraically is
indeed the ratio of
and and that the represents the phase relationship between
voltage and current.
0 0.2 0.4 0.6 0.8 1
Time (ns)
Graph 1
-0.1
-0.05
0
0.05
0.1
-20
-10
0
10
20
p2
p1
0.1189 ns
19.94 mA
0.2434 ns
0.07932 V
Vtime(M_PROBE.VP1,1)[*] (L, V)
Schematic 1
Itime(M_PROBE.VP1,1)[*] (R, mA)
Schematic 1
p1: Freq = 2000 MHz
p2: Freq = 2000 MHz
Conquer Radio Frequency
26 www.cadence.com/go/awr
