Conrinous DC versus pulsed DC sweep of RF transistor - question

On Tuesday, December 13, 2022 at 8:11:44 PM UTC+5:30, Fred Bloggs wrote:
> On Tuesday, December 13, 2022 at 1:19:41 AM UTC-5, daku...@gmail.com wrote: 
> > On Tuesday, December 13, 2022 at 2:28:34 AM UTC+5:30, Fred Bloggs wrote: 
> > > On Monday, December 12, 2022 at 3:02:04 AM UTC-5, daku...@gmail.com wrote: 
> > > > A question for the electronics gurus here. Recently I have done continous and pulsed DC sweep to examine the Ice - Vbe @ continuous and pulsed DC Vce for the SiGe BFQ790 transistor. 
> > > > In continous DC mode, the Vce is set at some allowed value(less than Vce max.) is swept over a lower - upper limit range, and Ice is measured. The the results are the familiar family of curves one finds in the date sheet. 
> > > > In the pulse Vce mode, the Vce is set at some allowed level, bit pulsed. The pulses are square wave, with predefined pulse width, period, rise amd fall times. Bit in the pulsed DC Vce case, the Ice values are always the dame, no matter what the amplitude of the Vce pulses are. 
> > > > Do the results for thr pulsed DC Vce reflect the fact that the parasitic capacitors and inductors in the transistors get discharged ehrn the Vce 
> > > > amplitude is zero ? I am trying to understand why for th pulsed Vce case, the Ice - Vbe curve is always the dame, no matter what the amplitude of the 
> > > > Vce pulses are. Thanks in adbvance for your hints|help|suggestions. 
> > > If you haven't removed the VBE drive between pulses, it will saturate the transistor for the next VCE pulse and cause ICE to jump to a constant value proportional to the stored saturation charge, Qsat. When you apply VCE, ICE will jump to Qsat/Tau, where Tau is the base transit time. ICE should decay over time to GmVbe due to recombination, but if you're using an incredibly brief VCE pulse, you won't see it. If you want to pulse things, you should be pulsing the VBE sweep instead of the VCE, unless you have some odd application in mind. 
> > I have tried both pulsed DC Vce and pulsed DC Vbe. With pulsed DC Vce, DC sweep of Vbe is done over the permitted range(as per datasheet), and with pulsed Vbe, DC sweep of Vce is done over the permitted range(as per datasheet). The Vbe|Vce pulse amplitude is varied within the applicable range(as per datasheet). The results are always the same: The pulse widths are 3 - 5 ms and periods are 6 - 10 ms. 
> > 1. With pulsed Vbe|Vce, the Ice values are always the same, no matter what the amplitude of the Vbe|Vce pulses are. or what the pulse widrh or period are, for each case. 
> > 2. With continuous Vbe|Vce, the familiar Ice -Vce|Vbe family of curves is obtained. 
> > _
> A functioning transistor will not behave as you describe. There must be something wrong with your test setup. Is the transistor plugged in wrong, or is there an issue with ICE to voltage conversion for the display, or some other problem? 
> Rule number one for engineers: If your test setup leads to the discovery of an entirely new property for the device under test -> something is wrong with the setup.

I am using a Keithley 6842 picoammeter and a Keithley 2230G triple output DC and programmable power supply. The same transistor is used for continous DC Vbe|Vce and pulsed DC Vbe|Vce. So if the continous DC Vbe|Vce method generates the correct family of curves, why would it fail in the pulsed DC Vbe|Vce case ? There are collector and base resistors as well.