Standard Time-Domain Example

After loading the 54120.demo.mdl model file, open the mdl8112 model for this example. This example demonstrates using an external signal generator with a scope. IC-CAP will not directly control the signal generator, so you must control it from its front panel. An HP 8112A 50 MHz pulse generator was used while developing this model.

In this example, the setup td_meas makes measurements assuming that an external signal generator (an HP 8112) is attached to the DUT and the scope. This arrangement provides much greater flexibility in the characteristics of the stimulus delivered to the DUT (the scope's pulse generator has limited flexibility, by comparison, with an instrument such as the HP 8112).

In this setup, waveforms are acquired on two scope inputs. Also, IC-CAP exercises the scope's ability to compute peak-to-peak and rms voltages. These computed voltages appear on the same plot as the waveforms, for visual comparison.

Measurement/Instrument Setup

The instrument setup includes an HP 54123T oscilloscope with an HP 8112A generator. You will need several BNC/APC-3.5 adapters.

Note: If the attenuators suggested on the scope inputs are not used, reduce the 8112 output signal below 320mV and adjust the Pulsed Value (in the input mdl8112/dut_8112/td_meas/ext_pulse) accordingly. (See Table 111 for details.) A suitable attenuator for 3.5mm connectors is part no. 33340C.

A 1 meter, 50-ohm cable is run from the Trigger output of the 8112, onto a 20dB attenuator on the Trigger input of the scope.

A 61cm 50-ohm BNC cable, 8120-1839, is run from the 8112's signal output to a BNC T-connector. The T feeds scope channel 1 through a 20dB attenuator. The T also feeds a1 meter, 50-ohm cable, 8120-4948, which feeds scope channel 4 through another 20dB attenuator. Add BNC/APC-3.5 adapters as needed.

By pressing the scope's LOCAL key and then its AUTOSCALE key, you can see if it is receiving trigger and input signals properly. (Two waveforms should appear on the scope's display.)

Be sure to issue the Rebuild command so the oscilloscope will be recognized by IC-CAP.

Simulation

The circuit for this model contains a transmission line to simulate the cable run from scope channel 1 to scope channel 4; this helps model the delay that will be apparent in the plotted waveforms. The circuit also contains 50-ohm resistors to simulate the loading offered by the channel 1 input and the channel 4 input. (These resistors would probably be more appropriately represented in a test circuit for the DUT dut_8112.)

The source impedance of the HP 8112 generator is automatically accounted for in the ext_pulse input, which exists in the setup td_meas. (See Table 111 for details.)

Setup specifics

Edit the td_meas setup (mdl8112) as described in the following input and output tables.

Table 111 Inputs

Input Name	Value/Description
time	This Input is necessary to specify the time window for which the measured and simulated data will be acquired. It uses the Mode T. Naming it time is not necessary. The start and stop times are selected so that several complete waveforms will be plotted.
ext_pulse	This Input describes the pulse stimulus, for Simulation purposes. For measurement, you should attempt to key in the same values on the front panel of the pulse generator being used. Note the following comments on some of the important fields: Mode: must be V + Node and - Node: points across which a simulated pulse is applied Unit: The special case GROUND is employed here to instruct IC-CAP to suppress the scope's own step generator. This makes it possible for the external pulse generator to be employed during measurement. By selecting Unit = GROUND, this ext_pulse input is effectively not used during the Measure menu selection. However, it is included for Simulate. Type: Must be TDR Pulsed Value: 3.3 was the value used to generate the measured data seen in the plot for this Setup. Unless you have 20dB attenuators on the scope inputs (a suitable attenuator for 3.5mm connectors is part no. 33340C), this value should be adjusted below 320mv, and the pulse generator should be adjusted similarly. Rise Time, Fall Time, Pulse Width: On the pulse generator, attempt to set these as shown in the IC-CAP Setup. Delay Time, Resistance: These were determined empirically using the HP 8112 to develop this demonstration. You may find different values give better agreement between the measured and simulated waveforms. Period: Enter the same value in the IC-CAP Setup and on the generator's front panel. 200n was used for the waveforms shown.

Table 112 Outputs

Output Name	Value/Description
wave1	This output will collect a waveform on the 1st input port of the scope. Note the use of CH1 to specify this. The Mode should be V. The simulated waveform is captured across the + and - Nodes shown.
wave4	This output will collect a waveform on the 4th input port of the scope. Note the use of CH4, and the Mode V. The simulated waveform is captured across the + and - Nodes shown. With the suggested cabling arrangement, the data of this output is slightly delayed, relative to the wave1 output.
vpp1	This output is only available for measurement (note the type M) because the oscilloscope computes it using special firmware algorithms. The Mode T is used to request these special Time-domain computations from the scope. By pressing the middle mouse button on the field Pulse Param, you can obtain help (in the Status panel) regarding the choices available from the scope. In this case, the peak-to-peak voltage associated with the measured part of wave1 will be obtained.
vpp4	This output is like vpp1, but obtains measured peak-to-peak voltage for CH4 and wave4.
vrms4	This output obtains measured RMS voltage for CH4 and wave4.