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Vpulse and Vsource

Shahnaf

Hi Andrew,

 I was trying to simulate rectifier circuit for which I simulated the circuit to test with different inputs -Sine and Pulse.

Initially, I tried using Vpulse and I observed some result. Then, I replaced Vpulse with Vsine and observed some other result.

 Then I have replaced Vsine with Vsource so that I change the type of input by changing the properties.

I have used the same parameters in Vsource which I have used in Vpulse, but I observed those two results are varying in a huge manner.

Can you please let me know why the difference is happening so? 

 

In the attached zip file, you can see 5 images. First is the snapshot of the circuit, which I have used for simulation.

Second image is the plot which I have captured, when simulated the circuit using source voltage as Vpulse and third is the plot with Vsource.

Similarly, fourth and fifth plots are captured, when simulated the circuit using source voltage as Vpulse and Vsource respectively.

I have used the same simulation parameters but I do see a change in the plots.

Can you please let me know why it is happening so when I use Vpul and Vsource though I have used zero and one values same in both sources? I have used pulse width as 1.15ns.

Thanks,

Shahnaz. 

 

rehi.zip
Parents

  • I can't really debug your circuit for you from a picture of the schematic in your first attachment and the waveforms in the new one. It does look a slight strange configuration - not quite sure what you're testing here. The bulk of the PMOS transistors is connected to the output - and there's no DC level for the gates - so there's quite a lot that's actually floating here - the behaviour of the PMOS transistors will be dependent upon what the gate and source voltages are relative to the bulk. The DC solution at the beginning of the simulation will be based on the time-zero values of the sources, and that will probably affect the initial voltage on the output capacitor - and you'll also get coupling through the junction capacitances on the transistor, as well as  the behaviour when (or if) the transistors switch.

    Remember that the DC solution (e.g. the initial transient solution) is based on setting all the capacitances (both explicit capacitors and the capacitances inside the transistor models) to 0, and solving the equations. With no DC path to ground, you'll get gmin resistors inserted at various places to try to come up with a DC solution - but that's going to be influenced by whatever the time zero value of the source is. You didn't say how the source is varying (what timescale), and whether these small variations are important (in none of the cases are the signal levels varying that much - it's just the starting point which is different).

    So I think it's possibly something to do with the DC starting point, but other than that, you'll need to figure it out yourself.

    Regards,

    Andrew.

Reply

  • I can't really debug your circuit for you from a picture of the schematic in your first attachment and the waveforms in the new one. It does look a slight strange configuration - not quite sure what you're testing here. The bulk of the PMOS transistors is connected to the output - and there's no DC level for the gates - so there's quite a lot that's actually floating here - the behaviour of the PMOS transistors will be dependent upon what the gate and source voltages are relative to the bulk. The DC solution at the beginning of the simulation will be based on the time-zero values of the sources, and that will probably affect the initial voltage on the output capacitor - and you'll also get coupling through the junction capacitances on the transistor, as well as  the behaviour when (or if) the transistors switch.

    Remember that the DC solution (e.g. the initial transient solution) is based on setting all the capacitances (both explicit capacitors and the capacitances inside the transistor models) to 0, and solving the equations. With no DC path to ground, you'll get gmin resistors inserted at various places to try to come up with a DC solution - but that's going to be influenced by whatever the time zero value of the source is. You didn't say how the source is varying (what timescale), and whether these small variations are important (in none of the cases are the signal levels varying that much - it's just the starting point which is different).

    So I think it's possibly something to do with the DC starting point, but other than that, you'll need to figure it out yourself.

    Regards,

    Andrew.

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