Radio Frequency Integrated Circuit Design - Webs

300 Radio Frequency Integrated Circuit Design
R ′cap = 2�1 + C 2
C 1� 2
3.83 pF
R cap = 2�1 +
4.72 pF� 2
3.1 k� = 20.3 k�
Thus, the total parallel resonator resistance is R p = 843�.
V tank ≈ 2I bias� C 1
C 1 + C 2� R p
I bias = V tank
2R � p C 1 + C 2 1.6V
C � =
1 2(843�)�
4.72 pF + 3.83 pF
4.72 pF
�
= 1.71 mA
The next thing to do is to size the transistors used in the tank. Transistors
were chosen to be 25 �m.
We can also estimate the phase noise of this oscillator.
The re of the transistor at this bias is
re = v T
IC
= 25 mV
= 14.8�
1.69 mA
Since this value will seriously affect our estimate, we also take into account
5� for parasitic emitter resistance (this value can be determined with a dc
simulation).
R re tank = 2�1 + C 1
C 2� 2
4.72 pF
re = 2�1 +
3.78 pF� 2
19.8� = 200�
This can be added to the existing losses of the overall resonator resistance
of 843� to give 162�.
Now we can compute the Q:
Q = R tank√ C total
L
= 162� √ 1.18 pF
4nH
We need to estimate the available power:
PS =
2
V tank (1.6V)2
= = 7.9 mW
2R tank 2(162�)
= 2.78
We can now estimate the phase noise of the oscillator. We will assume
that the phase noise due to K VCO is not important.