Appendix C

Analysis Tools

Analysis Tools

• Three major types of analysis:– DC analysis– AC analysis– Transient analysis

A Quick Tour of the Analysis

EWB does this…When you choose… DC

AnalysisAC

AnalysisTransient

DC Operating Point YesAC Frequency 1st 2nd

Transient 1st 2nd

Fourier YesNoise 1st 2nd

Distortion 1st 2nd

Parameter Sweep OptionalSweep

OptionalSweep

OptionalSweep

Temperature Sweep OptionalSweep

OptionalSweep

OptionalSweep

A Quick Tour of the Analysis

EWB does this…When you choose… DC

AnalysisAC

AnalysisTransient

Pole Zero YesTransfer Function YesDC Sensitive YesAC Sensitive 1st 2nd

Monte Carlo Optional Optional OptionalWorst Case Optional Optional Optional

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.

Example: Colpitts Oscillator

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

DC Operating Point analysis result

VoltAmpere

Direct measurement to the original circuit would not obtain these results.

Example: Colpitts OscillatorWhen running DC Operating Point Analysis, Multisim reduces the circuit like below:

Output voltage

Collector Current

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.

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

Example: 5V DC power supply

Setting AC frequency analysis parameters

Result

What can you comment for this frequency range?

Is this a distortion?

Gain versus

frequency

Phase versus

frequency

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.

Example: CMOS Inverter

Setting Transient analysis parameters

ResultInput voltage signal (Vin)

Output voltage signal (Vout)

What can you comment on the circuit response time?

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.

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.

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.

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.

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.

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:

Specifying output

• You need to also specify the output node of your circuit. In this case, node 5.

Results of Fourier analysis:

Need to scroll down to show the third component (which is the 10th harmonic)

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

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.

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.

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.

Example: Inverting amplifier

Setting Noise analysis parameters

Result

The thermal noise voltage produce by resistor R1

The thermal noise voltage produce by resistor R2

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.

Example: Class B push-pull amplifier

Setting Distortion analysis parameters

Result

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.

Example: CE amplifier

Setting DC sweep analysis parameters

Result

The collector voltage versus the collector source

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.

Example: RC circuit

Setting sensitivity analysis parameters

ResultChanges to resistor, R2 affect the circuit output for over a range of frequency

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.

Example: Colpitts Oscillator

Setting parameter sweep analysis parameters

Result

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 27C.

• Default temperature may be changed from the Analysis Options’ Global tab.

Example: Opamp comparator

Setting temperature sweep analysis parameters

Default temperatureSweep

parameter

Result

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.

Example: Inverting Opamp

Setting transfer function analysis parameters

Result

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.

Example: Wien-bridge oscillator

Setting Worst case analysis parameters

Result

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.

Example: LR passive filter

Setting Pole Zero analysis parameters

Result

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.

Example: RLC circuit

Setting Monte Carlo analysis parameters

Result