Download Exercise 2

Exercise 2
Parametric and Noise Analyses
I.
Parametric Analysis
1. Variable appearance
In Virtuoso Schematic Composer window do the draft from above.
The transistor nmos4 is real and you can find it in PRIMLIB library
for AMS 0.35 m CMOS technology. The length and width values are
set by default - w=10 m and l=0.3 m. The initial voltage sources (vdc),
which you use in simulation, are set in library analogLib. In the box
DC voltage of the input source, that gives the gate-source voltage, set
the variable Vgate. Copy that variable in ADE window (Analog Design
Environment) - go to Variables => Copy from cellview and set its
value by command Edit in the same menu.
2. DC settings
In order to set DC analysis, go to Analyses => Choose and check dc.
To take the final characteristics of MOS transistor you need the drainsource voltage range, so set this voltage source as a Component
parameter and put the values to be in the range of 0 to 3.3V.
In CADENCE system the voltage values on pins are kept by default. If
you wish to visualize the current values, you should save them
previously in Outputs => Save All and check the option Select all
DC/Transient terminal currents (if you use SpectreS simulator).
3. Setting Parametric Analysis
You can set the parametric analysis from menu Tools => Parametric
analysis. As an inconstant parameter set gate-source voltage with
variable Vgate. Let its value be in range 0 to 2.5V with 5 divisions.
4. Starting Simulation
From the same form go to menu Analyses => Start
5. Results visualizing
In order to visualize the output current when the simulation is over go
to menu Results => Direct Plot and choose dc. In Schematic editor
window select the drain transistor’s pin (fig. 2). The same result is if
you set the output current before the simulation is started: Outputs 
To Be Plotted  Select On Schematic.
In parametric analysis as variables you can set the transistors’
parameters width (w) and length (l) as well as frequency, temperature
and etc.
II. Noise Figure
To examine the noise figure use the schema shown below. It is necessary to
put sources which are used for noise examination (ports) on both input and
output. Those are psin from analogLib library. In the form for setting
parameters the only thing you have to fill is the number of the port which
should be a whole positive digit. For example: PORT0 - 1, and for PORT1 –
2. The coils (ind) and capacitors (cap) are ideal elements and you can take
them from analogLib. It is better to set to them high values – for the
capacity (mF ÷ F) and for the induction (mH ÷ H).
1. Setting Shared Parameters analysis (sp)
In ADE choose Analyses  Choose  sp. You should set the frequency
range for noise examination and the very noise sources as well – input
and output ports.
2. NF visualization
From menu Results choose Direct plot  S-parameter. In sp analysis
window check NF parameter. The result can be presented as an amplitude
value or to be kept in dB. Start the schematic drawing with pressing the
button Plot.
3. NF visualization and noise distribution on each elements included in the
circuit
Print  Noise Summary
Choose: Frequency spot: 2GHz
Filter  include: all types
Truncate&Sort: 10
In order to examine the NF factor in variety of gate voltages start the
parametrical analysis as you choose Vgate as a variable. The results for full
frequency range are shown on figure A and for high frequencies only the
results are shown on figure B.
Fig. A. MOS transistor NF factor for full frequency range
Fig. B. MOS transistor NF factor for high frequencies
NF analyses show the level of circuit stability regarding the interferential
electrical signals which can be not only with extraneous origin, but also
generated from the schematic elements.