voltage and current noise of op amp

[Roland1603]

Hello I use Multisim 11.0,

how can I watch the op amp voltage noise and the op amp current noise,

when building a simple non-inverting amplifier with op amp AD745

and watching the results in Simulate-> Analyse->Noise Analyses?

I just get the whole output spectrum (including op amp noise) and the noise caused by each resitor used for the non inverting amplifier, but not the noise caused by the op amp (voltage and current noise).

Is it possible to watch this noise sources separately?

Thanks Robert  

[TobiD]

Hi Robert,

first of all i wanna let you know that there are 2 examples regarding the "Noise analysis"

» Help » Find examples » Analysis » Noise analysis

There are two "Inverting amplifier" examples, which describes the noise analysis quiete good.

Anyway, in the Output Tab of the "noise analysis dialog" you can select different variables. There you can decide which variable you want to analyse- see the output help for more information:

Output Tab

Output Tab

This is where you choose the variables you want to use in the analysis.

Variables in circuit drop-down list—Use to select types of output variables to display in the list below. Choices are:
Static probes—Voltages at measurement probes and currents through measurement probes.
Circuit voltage and current—See Circuit voltage and Circuit current, below.
Circuit voltage—Voltages at circuit nodes, referenced to node 0.
Circuit current—Currents through voltage-output devices and the inductor device. Voltage-output devices include the independent voltages source, the controlled voltage source, and the voltage-output arbitrary sources. These currents are singled out from other device currents (for example, resistor current) because these currents appear naturally as variables in the matrix that is used to solve the circuit.
Device/Model Parameters—These are either manually placed in the list using the Add Device/Model parameter dialog box, or are automatically placed in the list by Multisim because it considers these parameters important. Important parameters include the current and power parameters of many commonly used devices such as resistors, capacitors, and diodes. Multisim will only pull these parameters into the list if the corresponding devices are outside of all subcircuits (.subckt statements) within the netlist. For example, if you need to plot the power across a resistor that is within an op-amp .subcircuit model, you must manually place that parameter in the list because Multisim will not do this automatically. This behavior exists to avoid flooding the variables list with an excessive amount of items.

   Note  Devices are the primitive circuit elements that are in the circuit netlist; they are not components on the schematic. While it is often the case that a component's symbol may represent the single device that makes the component's model (for example, most diode components in the database have a single diode device as the model), a component's symbol often has no bearing on the devices that make up its model. Therefore, you should be aware of the actual device whose parameters are being queried.

All variables—Populates the list with all of the above.
Filter unselected variables button—Use to filter types of variables displayed.
Add device/model parameter button—Use to add a parameter from a specific device or model to the list of variables. Refer to the Adding Parameters to the Variable List section for more information.
Selected variables for analysis drop-down list—Use to choose types of variables to be used in analysis.
Filter selected variables button—Use to filter the variables displayed to include internal nodes, open pins and output variables.
Edit expression and Add expression buttons—Use to add and edit analysis expressions.
Select variables to save button—Use to select variables to save that can be used to add trace s to a graph after simulation, or for postprocessing. See Selecting Variables to Save.

Regards,

Tobias

[patkins]

Hi Robert,

I know its a bit old to be replying to this post, but can you relocate the links in your answer as they seem to have gone dead and I'm trying to nail down some info on output variable in noise analysis.

Thanks

Paul