[SOLVED] currents through different elements in the same branch are not equal...

[bearhuhu]

Dear all,

I have a branch in which a resistor is in series with N parallel diode-connected BJTs. However, after the dc analysis, when i annotated the dc node voltage and dc operating points, i found out the current flowing through the resistor was 300nA while the total current flowing through N BJTs was only 200nA. Since the resistor is in series connection with the BJTs, the current flowing through them should be the same. I don't understand why this is happening. Is this because of the leakage, or something else?

Thank you!

Best regards,

Joya

 

[crutschow]

Post the schematic.

 

[sam_icdesign]

Post the schematic.

of entire circuit with any in out terminals . Also, DC operating points

 

[bearhuhu]

Hi Crutschow, Sam,

The image contains the whole schematic and the DC operating points. The OTA is an ideal one.

The branch i am talking about is the R3 in series with D2. R3 = 393kohm.

 

[godfreyl]

The image contains the whole schematic and the DC operating points.

According to that, the collector current Ic = 200n and beta = 2.
Therefore the base current Ib = 200n / 2 = 100n.
So the total current through the diode-connected transistor = Ic + Ib = 300n, same as through the resistor.

 

[bearhuhu]

I see, thank you very much!

- - - Updated - - -

According to that, the collector current Ic = 200n and beta = 2.
Therefore the base current Ib = 200n / 2 = 100n.
So the total current through the diode-connected transistor = Ic + Ib = 300n, same as through the resistor.

I am kind of confused. Why the betadc is so small as 2? Which parameters determine betadc? I read in Gray's book, it said typical values for betaf are 10~100. What about the betadc?

Thank you!

 

[keith1200rs]

Lateral PNPs have pretty small beta in small geometries. Some of them aren't much better than diodes ;-)

Keith

 

[bearhuhu]

Lateral PNPs have pretty small beta in small geometries. Some of them aren't much better than diodes ;-)

Keith

Thank you Keith! I think i will keep it in mind!