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

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#### bearhuhu

##### Newbie level 4
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

Post the schematic.

Post the schematic.

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

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.

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.

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!

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

Keith

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!

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