Changes

==Using Probes or Meters as Observables==

A simpler way of defining voltage and current observables is using "Probes". [[RF.Spice A/D]] provides two types of probes: Voltage Probes and Current Probes. Both can be accessed from the Schematic Toolbar at the top of the screen or by selecting "Probe Mode" in the Schematic Editor's Edit Menu. The keyboard shortcut "Ctrl+P" can be used for this purpose, too. While in the Probe Mode, you can place as many probes as you want. Voltage probes must be placed at the circuit nodes or on the wires, while current probes must be placed on a device pin. Voltage signal are always measured with respect to the circuit's ground. The direction of a current signal is determined by its underlying device pin, which shows the current's entrance into the device. The opposite figure shows a typical operational amplifier (Op-Amp) circuit with two voltage probes placed at its input and output nodes. The figure below it shows a graph of the plotted probe voltages.

Similarly, placing voltmeters, ammeters or wattmeters in your circuit always forces [[RF.Spice A/D]] to calculate the respective voltages, currents or powers during each simulation, whether a live simulation or a predefined test.

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==Generating a Spectrum Graph from Time-Domain Data==

With [[RF.Spice A/D]], you can compute the Fourier Transform of your time-domain data and generate a spectrum graph. The "Transient Test Setup" dialog has an option called "Apply Fourier" that automatically creates a bar chart at the end of the simulation, showing the spectral contents of your time-domain waveform. Another option to perform a "Fast Fourier Transform" (FFT) on your data is the "Spectrum Graph" that can be accessed from the Graph View's "Special Functions" menu or from the Graph Toolbar. Unlike the transient test's Fourier bar chart, a spectrum graph is a Cartesian graph. In the transient test's Fourier Analysis, you have to specify a "Fundamental Frequency". The spectral contents of your signal are then calculated at the fundamental frequency and its harmonics (i.e. integer multiples of the fundamental frequency). In the spectrum graph, you already have time-domain data over a time window, which is usually from t = tmin to t = tmax. The fundamental frequency of the FFT is automatically calculated as f0 = 1/(tmax - tmin).

To generate a spectrum graph, choose "Create Spectrum graph" from the Graph view's Special Functions Menu, or click the "FFT" button on the Graph Toolbar. This opens up the FFT Settings Dialog. At the top of the dialog, you have to select the "Target Signal" from a drop-down list. In the Sampling Options section of the dialog, you will see the start and stop times. You can change your temporal window if necessary. At the top of this section you can specify the "Number of Intervals" from a drop-down list with powers of 2. The default value is 512.

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