Direct beta measurement using current division? Possible?

[Someone]

Temperature compensation? "Isothermal"? Not bothered; again, not looking to create any kind of high-precision instrument here. Those who like to DIY will understand. Good enough may be good enough.

AS mentioned in your other thread covering this topic. Quantify your errors and what is acceptable. For all the hand waving and not caring, Ib << Ic is enough to cancel the Ib contribution within your accuracy so adding that back in is entirely pointless unless you also control the other sources of error.

If you ignore the I_b part of the emitter current, you need only add +1 (exact) to the ratio I_e / I_b to get the usual definition of {beta} = I_c / I_b.
If {beta} > 50 (for example), this is a small correction to the ratio at the value of emitter current you obtain from the circuit.

And what is the magnitude of that correction (and error) in comparison to the effects of thermal drift ? Engineering.

[Analog Kid]

OK, I'm getting annoyed here: going forward, let me declare something regarding this project:

Fuck accuracy. Just ignore it.

The point of this exercise is not to develop a super-accurate instrument that might have commercial or industrial application.

The point is to play with an intriguing (to me) circuit, and to see if there's any practical way to bend it to my usage (here a transistor beta tester). So can we please just dispense with the nitpicking about accuracy, tempco, all that stuff?

[ArdWar]

how would one get those two currents from the D.U.T. (I_B & I_C) into the Gilbert cell here?

Telegraphing current between two otherwise separate loops are what a current mirror is for. Mind your error budget tho

[Analog Kid]

Now we're getting somewhere. Thank you! Yes, a current mirror did occur to me. (And of course every additional piece here will add its error, sure.)

Something like this?



Let me revise my inflammatory statement above a bit: to the point where the overall accuracy is not swamped by errors I'll continue to pursue this project; if it becomes clear that errors would swamp any valid results, then I'll consider abandoning it. Fair enough?

[iMo]

OK, I'm getting annoyed here: going forward, let me declare something regarding this project:

Fuck accuracy. Just ignore it.

The point of this exercise is not to develop a super-accurate instrument that might have commercial or industrial application.

The point is to play with an intriguing (to me) circuit, and to see if there's any practical way to bend it to my usage (here a transistor beta tester). So can we please just dispense with the nitpicking about accuracy, tempco, all that stuff?

While reading this thread (and the previous one of Kid) I wonder how many various circuits do exist in electronics actually, how many of them could be somehow reused for measuring the beta, and how many of those will be suggested by Kid here for a discussion, moderated in his/her/it lovely style.. 

[Analog Kid]

Wellll, the answer to your first question is obviously "lots".
As to what else I might suggest in this line--maybe something using a cesium time base, perhaps one or more lasers?--I think my current curiosity/obsession is sufficient for now. Until the next one comes along ...

[magic]

I suppose you could try something like that...

N1 are relatively high current types like BC337 or 2N2222, all same type, matched for Vbe.
N2 can be anything, but preferably high beta.
D1 is anything.
Ic sets test collector current.

Ic(Q6)/I(Iscale) is supposed to be β of Qtest.

[Analog Kid]

Thank you for that. But some questions:
You obviously altered the Gilbert cell schematic I posted; may I ask why? did you somehow improve it?
What is the function of the diode?
Why wouldn't all the transistors (except the D.U.T.) be the same type?

[magic]

Well, for starters, there is now a place to plug a (PNP) transistor and measure its beta, while the circuit you found on SE had nothing like that. I hope this counts as an improvement for your purpose

Substantially, it's still the same thing:
Vbe(Q6) = Vbe(Q1) + (Vbe(Q3) - Vbe(Q5))
Ic(Q6) = Ic(Q1) · (Ic(Q3) / Ic(Q5))

Q2 is an emitter follower which reduces Q3 base current influence on Iscale. Do the maths and you will see why it's important.
Q4 regulates Q5 current to produce the exact correct base current into Qtest. It also makes the circuit insensitive to Q6 base current.
D1 is a kludge. Q3 collector voltage is quite low (~1.2V) but Q2 must be higher or it would saturate. D1 separates them.