Rbe test circuit?

[Rene Schmitz]

So it seems to me that the best circuit to test it is an actual 
VCO application circuit, leakage and constancy of the cap are 
perhaps of minor importance, since the measurement would set an 
ordinary VCO into the kHz range, where the leakage can be neglected, 
and you can have many measurements in a small time interval. (i.e. before 
the cap undergoes drastical capacitance drift)
But I *do* think that the integrator reset time has an impact on the 
measurements. But before I can start I'll have to make a little frequency 
counter.  

At 07:34 19.07.99 +0200, Martin Czech wrote:

>Ok, I said collector current because that's what you really want.
>So perhaps one should do a linear diode plot (because the rbe will be the
>linear thing in the plot). And maybe another plot with collector current,
>one can varry collector voltage to get an idea of the Early then.
>
>Getting parameters is difficult, you can really just get plots
>and try to fit the theoretical values of theoretical devices
>afterwards. 
>
>And I guess you need quite accurate measurement gear.
>
>
>Perhaps this all can be avoided if one uses an oscillator for time
>integration of the current, whith low leakage high value cap ( will
>eliminate time errors) and known low Ibias buffer (will eliminate
>current error).
>
>m.c.
>

At 11:49 19.07.99 -0500, Grant Richter wrote:

>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.




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