2. Analysis Tools
• Three major types of analysis:
– DC analysis
– AC analysis
– Transient analysis
3. A Quick Tour of the Analysis
EWB does this…
When you choose… DC
Analysis
AC
Analysis
Transient
DC Operating Point Yes
AC Frequency 1st
2nd
Transient 1st
2nd
Fourier Yes
Noise 1st
2nd
Distortion 1st
2nd
Parameter Sweep Optional
Sweep
Optional
Sweep
Optional
Sweep
Temperature Sweep Optional
Sweep
Optional
Sweep
Optional
Sweep
4. A Quick Tour of the Analysis
EWB does this…
When you choose… DC
Analysis
AC
Analysis
Transient
Pole Zero Yes
Transfer Function Yes
DC Sensitive Yes
AC Sensitive 1st
2nd
Monte Carlo Optional Optional Optional
Worst Case Optional Optional Optional
5. DC Operating Point Analysis
• To determines the DC operating point of a circuit.
• Results are DC node voltages and branch currents.
Setting for DC analysis:
– AC sources are zeroed out.
– Steady state is assumed:
• Capacitors are open circuits.
• Inductors are short circuits.
– Assumptions:
Digital components (such as IC’s) are treated as large resistances to
ground.
7. Setting DC Operating Point analysis parameters
• There is no analysis parameters to be set.
• User able to select which voltages or branches to
analyze.
Available voltage
nodes
Available Current
branches
Selected
variable for
analysis
8. DC Operating Point analysis result
Volt
Ampere
Direct measurement to
the original circuit would
not obtain these results.
9. Example: Colpitts Oscillator
When running DC Operating Point
Analysis, Multisim reduces the
circuit like below:
Output voltage
Collector Current
10. AC Frequency Analysis
• To determines how the circuit behave to a range of
frequency.
Setting for AC analysis:
• The DC operating point is first obtained for non-linear
circuit.
• All input sources are considered to be sinusoidal.
• The frequency of the sources is ignored.
• The AC simulation is done based on a sweep over a range
of frequencies.
11. AC Frequency Analysis
• Assumptions:
Analogue circuits, small signal.
Digital components are treated as large resistances to
ground.
• The result is displayed on two graphs:
– Gain versus Frequency
– Phase versus Frequency
Similar to using Bode
Plotter for measurement
14. Result
What can you comment for this frequency
range?
Is this a
distortion?
Gain
versus
frequency
Phase
versus
frequency
15. Transient Analysis
• Also called Time-domain analysis.
• Closely simulates the phenomena seen in the real circuit
by means of an oscilloscope.
• To determines how the circuit behave over time.
• A simulation consists usually of a time sweep starting at
time, t = 0.
• The result of the transient analysis is a graph of voltage
versus time.
18. Result
Input voltage signal (Vin)
Output voltage signal (Vout)
What can you comment on the circuit response time?
19. Fourier Analysis
• A method to analyze complex periodic waveforms.
• It permits any complex periodic waveforms to be
resolved into sine or cosine waves and a DC component.
• This permits further analysis and allows you to determine
the effect of combining the waveform with other signals.
20. Fourier Analysis
• The Fourier analysis is basically the same as
spectrum analyzer.
• The only difference is, the spectrum analyzer runs
continuously, reflecting any changes in the
harmonics of the input waveform, whereas the
Fourier analysis performs the analysis only within a
specified period of time.
21. Setting
• Do not worry about setting the frequency resolution.
When not sure what to do, just press the “estimate”
button to have the software estimate for you.
22. Estimate
• The software estimated the fundamental frequency of our complex
waveform to be 5 kHz.
• Isn’t our lowest frequency 10 kHz? Well, yes, but that is not the
fundamental frequency. The fundamental frequency should be the
lowest common factor of all the frequencies. In this case, precisely
5 kHz.
23. Number of harmonics
• In our case, we need at least 10 harmonics to show the
50 kHz harmonic. (Our fundamental is 5 kHz, so 50 kHz
is the 10th
harmonic.) But we will set the number of
harmonic to 20, assuming we do not know the answer.
24. Stopping time
• As mentioned before, fourier analysis is only performed
for a fixed period of time. So, we need to specify that
period of time as well. Let us make our setting as 0.01
s:
25. Specifying output
• You need to also specify the output node of your
circuit. In this case, node 5.
26. Results of Fourier analysis:
Need to scroll down to show
the third component (which is
the 10th
harmonic)
27. Noise Analysis
• Noise is any undesired voltage or current appearing in the
output.
• One common result of noise is “snowy” television
reception caused by fluctuations across all frequencies of
TV signal.
• Multisim can model 3 kinds of noise:
– Thermal noise
– Shot noise
– Flicker noise
28. Noise Analysis
• Thermal noise
– Is temperature dependent and caused by the thermal
interaction between free electrons and vibrating ions in a
conductor.
– Its frequency content is spread equally throughout the
spectrum.
29. Noise Analysis
• Shot noise
– Cause by the discrete-particle nature of the current carriers in
all forms of semiconductors.
– The major cause of transistor noise.
– The equation for shot noise in a diode is given as below.
– For other devices such as transistors, no valid formula is
available. Provided in manufacturer’s data sheet.
30. Noise Analysis
• Flicker noise
– Also known as excess noise, pink noise or 1/f noise.
– Present in BJT and FET and occurs at frequencies below 1kHz.
– It is inversely proportional to frequency and directly
proportional to temperature and DC current levels.
34. Distortion Analysis
• Distortion analysis is a type of transient analysis that
applies a single frequency sinusoidal signal to the input
source and measures the resulting distortion in the
specified output.
• Signal distortions are usually the result of gain non
linearity or phase non uniformity in a circuit. Nonlinear
gain causes harmonic distortion, while non uniform
phase causes inter modulation distortion.
• Distortion analysis is useful for investigating small
amounts of distortion that are normally un-resolvable in
transient analysis.
38. DC sweep analysis
• To quickly determines the DC operating point of your
circuit by simulating it across a range of values for 1 or
2 DC sources.
• The effect is the same as simulating the circuit using DC
operating point analysis several times with different
values.
42. Sensitivity analysis (DC and AC)
• Sensitivity analysis help to identify the components
which affect a circuit’s DC bias point the most.
• This will focus efforts on reducing the sensitivity of the
circuit to component variations (or drifting).
• It may provide evidence that a design is too
conservative and that less expensive components, with
more variation may be used.
46. Parameter Sweep Analysis
• A function that able to perform 3 types of sweeps:
– DC operating point analysis
– Transient analysis
– AC frequency analysis
• You will find that some components have more
parameters to perform a sweep. While others, such as
inductors has only inductance available as a parameter
for analysis.
50. Temperature Sweep Analysis
• Quick verification of circuit behaviour towards
temperature changes.
• Similar to simulating the circuit several times, once for
each different temperature.
• Default temperature is 27°C.
• Default temperature may be changed from the Analysis
Options’ Global tab.
54. Transfer function analysis
• Transfer function analysis calculates the DC small-signal
transfer function between an input source and two
output nodes (for voltage) or an output variable (for
current) in a circuit.
• It also calculates input and output resistances.
58. Worst case analysis
• Worst case analysis is a statistical analysis that lets you
explore the worst possible effects of variations in
component parameters on the performance of a circuit.
62. Pole Zero Analysis
• Finds the poles and zeros in the small-signal AC transfer
function of a circuit.
• Useful in determining the stability of electronic circuits.
Stable circuits should have poles on negative real parts.
• Note: May occasionally receive message such as:
“Pole-zero iteration limit reached, giving up after 200 iteration”
Even with this message, the analysis may still have found
all the poles and zeros.
66. Monte Carlo Analyses
• Statistical analysis that allows explorations in affects
brought by component properties variations.
• The first simulation is always performed with nominal
values.
• For the rest of the simulations, a delta value is randomly
added to or subtracted from the nominal value.
• The tolerance percentage is applied globally.
