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PSPice Ftable Parameters

Daniel P

Hi there.

I'm developing a circuit in PSpice including an Impedance-model, which is simulated within a real and a complex part. Also can be looked like a Resistor and a Capacitor that change values according to varying the frecuency.

So, for example, I have:

@35kHz: R=2000; C=2.27nF or also can be modeled like 0-2000j or |Z|=2000 and Phase=-90º

... 

@39kHz: R=1550; C=2.39nF or also can be modeled like 202.32-1536.7j or |Z|=1550 and Phase=-82.5º 

 

and so on, until 45kHz (steps can be from 250Hz). 

 

When I try to insert this behavior into my Schematic, using FTABLE Part, I cannot get the right way to simulate whe whole circuit (the output I get has no-sense).

I know the circuit is well designed because if I put single values of a Resistor and a Capacitor instead of the FTABLE componet, I get a correct output. But that's not a polite solution, because I have many values for these components.

I'm trying to set up the FTABLE like this (Parameters are in Modulus and Phase Expression mode)

 

row1: 35kHz    2000         -90

row2: 38.5kHz     1650       -86.25

row3: 39kHz     1550       -82.5 

row4: 41.750kHz     2100       -88

row5: 45kHz     1800      -90 

 MAGUNITS=mag

 

What am I doing wrong? Do I need to change other parameters or settings in the FTABLE setup? Is there other way to do what I'm trying to?

Thank you in advance, any help will be much appreciated.

Regards,

D. 

 

Parents



  • Refer the attached design. In this design GTABLE device is used to simulate microphone. The value shown in table does not represent the actual microphone characteristics for complete frequency range. These value are indicative in nature. I have calculated and put in value for only one frequency, that is 40KHz to explain the concept. Here load (microphone) is modeled using G table and this is connected to source V2. Source V1 is dummy in nature. In this specific circuit configuration, microphone is supposed to be connected between V2 and ground.

    In simulation results, at 40KHz frequency, you would see that overall impedance seen by source(V2) is ~400 Ohms. This is in line with value shown in impedance curve (shown in your append). Similarly you can see phase value is ~6 degree at 40KHz. This is also in line with value shown in microphone curve. Based on microphone impedance curve, it should behave largely as resistive element (since phase is ~0 degree), and hence major contribution to impedance would be largely due to resistive component (~400 ohms). I have tried to show the same by separate RC circuit in same design. At 40KHz, chosen RC (397.8 Ohms, 96n) value seems to offer similar impedance characteristics.


    Calculating the GTable parameters:

    Phase value can be directly obtained from microphone impedance curve.

    Since magnitude need to be defined in DB, it should be calculated using impedance value (400Ohms @40KHz), input voltage source magnitude (1V). G device is voltage controlled current source: which is current at output terminal for a given voltage at input terminal, thus I/V is my transfer function (gain or attenuation). If you plot the Gain/phase plot for RC circuit, you would see the similar (used in GTABLE device) value for gain/phase as seen by source V3.

    If you simulate and plot impedance seen by V2 and phase of current flown from V2, you should see plot similar to one shown in microphone impedance curve. Since this is plotted using only 4 data point this seems bit erratic, however it follows similar variations. This waveform can be further smoothen up using more data points in table.


    I hope this make sense, explains use of GTABLE device to simulate impedance and you find this relavent for your case.

    GTABLE.zip
Reply



  • Refer the attached design. In this design GTABLE device is used to simulate microphone. The value shown in table does not represent the actual microphone characteristics for complete frequency range. These value are indicative in nature. I have calculated and put in value for only one frequency, that is 40KHz to explain the concept. Here load (microphone) is modeled using G table and this is connected to source V2. Source V1 is dummy in nature. In this specific circuit configuration, microphone is supposed to be connected between V2 and ground.

    In simulation results, at 40KHz frequency, you would see that overall impedance seen by source(V2) is ~400 Ohms. This is in line with value shown in impedance curve (shown in your append). Similarly you can see phase value is ~6 degree at 40KHz. This is also in line with value shown in microphone curve. Based on microphone impedance curve, it should behave largely as resistive element (since phase is ~0 degree), and hence major contribution to impedance would be largely due to resistive component (~400 ohms). I have tried to show the same by separate RC circuit in same design. At 40KHz, chosen RC (397.8 Ohms, 96n) value seems to offer similar impedance characteristics.


    Calculating the GTable parameters:

    Phase value can be directly obtained from microphone impedance curve.

    Since magnitude need to be defined in DB, it should be calculated using impedance value (400Ohms @40KHz), input voltage source magnitude (1V). G device is voltage controlled current source: which is current at output terminal for a given voltage at input terminal, thus I/V is my transfer function (gain or attenuation). If you plot the Gain/phase plot for RC circuit, you would see the similar (used in GTABLE device) value for gain/phase as seen by source V3.

    If you simulate and plot impedance seen by V2 and phase of current flown from V2, you should see plot similar to one shown in microphone impedance curve. Since this is plotted using only 4 data point this seems bit erratic, however it follows similar variations. This waveform can be further smoothen up using more data points in table.


    I hope this make sense, explains use of GTABLE device to simulate impedance and you find this relavent for your case.

    GTABLE.zip
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