Spice Simulation dosen t correspond to the hand calculation ..a basic circuit

[jigsaw55]

Hi everybody
ı ve a problem with the circuits in the attachment ı think somethings go wrong.. ı found the dc bias point 2V the node showed with arrow by hand calculation but in the spice simulation it s -0.47mV ı gave the parameters in the attachment..İf anyone see how can be ,please explain. this is a basic circuit and my homework .. ı can go mad

 

[alec_t]

ı found the dc bias point 2V the node showed with arrow by hand calculation but in the spice simulation it s -0.47mV

I don't see any '-0.47' on the screenshot. The arrow seems to point to the source of M7, and that's apparently at -1.643.
BTW, all the FETs are switched on simultaneously. Is that intended?

 

[jigsaw55]

ooh no sorry the arrow isnt on the correect place i put it to show . I tried to mention the drain of M6 which is -428.9 mV.. the gate of m6 is 1.5V how can it be? . Is trazistors in triode active mode here? but it must not. because I will find the gain phase ..and apply it a unity feedback

 

[alec_t]

but it must not. because I will find the gain phase ..and apply it a unity feedback

Not understood. Ask someone to express that in plain English, or use Google Translate.

 

[jigsaw55]

yeah u are right my english is not good...forget that part of my question ..the question is that I found 2V the drain voltage of the M6 by hand calculation, it is reasonable but in the simulation it shows -428.7 mv.. Where is my false on the simulation ?

 

[alec_t]

You have all the FETs switched on fully in the sim, but you are trying to force a 0.5mA current through them. The simulator is getting confused. Try putting some resistors in series with the FET drains or sources.

 

[jigsaw55]

I cant do that because this is given me as a homework ı think the spice program which i use has something wrong because it is cracked..can it be ?But it worked properly before

 

[ericgibbs]

I cant do that because this is given me as a homework ı think the spice program which i use has something wrong because it is cracked..can it be ?But it worked properly before

hi,
This is what I see with LTspice

 

[jigsaw55]

yeah this is ...values are reasonable..and this shows my pspice program fails.
so thank you everybody

 

[crutschow]

You have an ideal current source (I1) in the source connection of M6 and M7. A current source in Spice will draw the designated current no matter what the rest of the circuit does. Here it is creating a negative voltage to generate the required current because the gate voltages at M6 and M7 are not high enough to generate the 0.5mA current value (what it the threshold voltage of those?). Try increasing those gate voltages.

Since an ideal current source is not a real component you should substitute a real current source using a transistor. Then your bias values will be more realistic.

 

[jigsaw55]

You have an ideal current source (I1) in the source connection of M6 and M7. A current source in Spice will draw the designated current no matter what the rest of the circuit does. Here it is creating a negative voltage to generate the required current because the gate voltages at M6 and M7 are not high enough to generate the 0.5mA current value (what it the threshold voltage of those?). Try increasing those gate voltages.

Since an ideal current source is not a real component you should substitute a real current source using a transistor. Then your bias values will be more realistic.

but i cant make any change ..it is homework ..vto is given as 0.7V.. and also ericgibbs 's ltspice did it properly.