Rbe test circuit?

[Grant Richter]

Plotting the voltage or current deviation form the theoretical line
would take a 5 or 6 1/2 digit DVM. Real pricey.

I think an exponential VCO is probably your best test circuit.
The effect of the Rbe is known (VCO goes flat on high end).
You can at least qualify the effect for different trannie pairs.

You could almost look at it as a custom current to frequency
converter for testing Rbe. Since the frequency is easy to
measure on a counter. That is how many of the meter circuits
work anyway, integrate the current with a comparator and counter.
You can neglect the comparator switching time since that is
fixed.

----------
> From: Rene Schmitz <uzs159 at uni-bonn.de>
> To: Martin Czech <martin.czech at intermetall.de>; synth-diy at mailhost.bpa.nl
> Subject: Re: Rbe test circuit?
> Date: Friday, July 16, 1999 10:59 AM
> 
> At 09:11 16.07.99 +0200, Martin Czech wrote:
> >:::Or measuring Vbe with variing collector current?
> >:::Any better ideas?
> >
> >since the rbe effect is mostly in higher Vbe, and you go for expo
> >applications... yes , I guess this would be an idea. I would also
measure
> >Ib, and I would try to have Ie constant, like in the moog circuit.
> >
> >Of course, one should check this with an almost ideal tranny,
> >any MAT02 left ? I have two which I have never used...
> >
> >m.c.
> >
> 
> After thinking about it, I come to the conclusion that the collector must
> be open,
> since the Early effect would change the Vbe too.
> I think perhaps the way would be to draw the Vbe/Ib courve on log paper.
> (Did I say paper?!, I mean gnuplot or something!) For an ideal device I'd
> expect a straight line (just Ebers Moll). In real devices for higher base
> currents there should be a deviation from the straight line. But this
would
> be difficult to measure, since I think the deviation perhaps is already
> swamped in the error bar. At some hundred uA of base current the input
> resistance is maybe still in the range of some hundred Ohm.
> Btw, Would it be perhaps possible to get the value for R(be) from the
> h-parameters?
> Like extrapolating h(ie)vs Ic for Ic -> inf. If Ic (thus Ib) is very
large,
> and therefore the B-E diode's dV/dI very small, the remaining value would
> be the static Rbe (???).
> 
> Bye
>  René
> 
> 
> 
> 
>              ,   : (uzs159 at uni-bonn.de)
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