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From: Jim Thompson on 14 May 2010 15:02 On Fri, 14 May 2010 11:28:31 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Fri, 14 May 2010 12:18:27 -0500, Vladimir Vassilevsky ><nospam(a)nowhere.com> wrote: > >> >> >>John Larkin wrote: >>> On Fri, 14 May 2010 10:59:21 GMT, Jan Panteltje >>> <pNaonStpealmtje(a)yahoo.com> wrote: >>> >>> >>>>On a sunny day (Thu, 13 May 2010 17:48:41 -0700) it happened John Larkin >>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >>>><i37pu594178305v2a62vb99d263og1tfau(a)4ax.com>: >>>> >>>> >>>>>I like this as a test: >>>>> >>>>> >>>>> >>>>> +10V >>>>> | >>>>> | >>>>> | >>>>> | >>>>> c >>>>> +5V--------------b >>>>> e >>>>> | >>>>> | >>>>> 1K >>>>> | >>>>> | >>>>> | >>>>> | >>>>> gnd >>>>> >>>>> >>>>>What's the base voltage? >>>>> >>>>>What's the base current? >>>>> >>>>>What's the emitter voltage? >>>>> >>>>>What's the collector current? >>>>> >>>>>What's the collector voltage? >>>>> >>>>>Any other comments? >>>>> >>>>> >>>>>I'm not kidding. One "experienced ee" said that, since the transistor >>>>>is saturated, the collector voltage is zero. A tech applicant said >>>>>that the base voltage is 0.6. >>>>> >>>>>Some people got it right, but nobody has mentioned oscillation so far. >>>>> >>>>>John >>>> >>>>How many asked if it was germanium or Si? >>>>Would be my first question. >>> >>> >>> An interviewee could certainly ask questions, or mention assumptions. >>> >>> Can you still buy germanium transistors? Would that affect many of the >>> answers much? >> >>You can buy germanium transistors in China if you need them. It is kinda >>nostalgic to see old style metal cans. >> >>BTW, on the matter of Jan's questions: 90% of experienced EEs think that >>Vce is 0.6V for silicon BJT in saturation mode. This misconception is >>surprisingly common. > > >Really? I didn't know that 90% of EEs were that dumb. That's >terrifying. > >I recently did some saturation measurements on a BCX70 and was >surprised myself... but at least I didn't expect 0.6. > >ftp://jjlarkin.lmi.net/BCX70_curves.pdf > > >I bet few EEs know how to make an NPN saturate to exactly 0 volts. > >John Show us, John. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: Vladimir Vassilevsky on 14 May 2010 15:54 John Larkin wrote: > On Fri, 14 May 2010 12:18:27 -0500, Vladimir Vassilevsky > <nospam(a)nowhere.com> wrote: >>BTW, on the matter of Jan's questions: 90% of experienced EEs think that >>Vce is 0.6V for silicon BJT in saturation mode. This misconception is >>surprisingly common. > > Really? If you don't know how it works, the 0.6V answer seems very intuitive. > I recently did some saturation measurements on a BCX70 and was > surprised myself... but at least I didn't expect 0.6. > > ftp://jjlarkin.lmi.net/BCX70_curves.pdf > > > I bet few EEs know how to make an NPN saturate to exactly 0 volts. BJTs in perverted mode may saturate to few mV, but it won't be exactly zero. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
From: Jim Thompson on 14 May 2010 16:18 On Fri, 14 May 2010 14:54:33 -0500, Vladimir Vassilevsky <nospam(a)nowhere.com> wrote: > > >John Larkin wrote: > >> On Fri, 14 May 2010 12:18:27 -0500, Vladimir Vassilevsky >> <nospam(a)nowhere.com> wrote: > >>>BTW, on the matter of Jan's questions: 90% of experienced EEs think that >>>Vce is 0.6V for silicon BJT in saturation mode. This misconception is >>>surprisingly common. >> >> Really? > >If you don't know how it works, the 0.6V answer seems very intuitive. > >> I recently did some saturation measurements on a BCX70 and was >> surprised myself... but at least I didn't expect 0.6. >> >> ftp://jjlarkin.lmi.net/BCX70_curves.pdf >> >> >> I bet few EEs know how to make an NPN saturate to exactly 0 volts. > >BJTs in perverted mode may saturate to few mV, but it won't be exactly zero. > > >Vladimir Vassilevsky >DSP and Mixed Signal Design Consultant >http://www.abvolt.com Indeed :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: John Larkin on 14 May 2010 17:10 On Fri, 14 May 2010 14:54:33 -0500, Vladimir Vassilevsky <nospam(a)nowhere.com> wrote: > > >John Larkin wrote: > >> On Fri, 14 May 2010 12:18:27 -0500, Vladimir Vassilevsky >> <nospam(a)nowhere.com> wrote: > >>>BTW, on the matter of Jan's questions: 90% of experienced EEs think that >>>Vce is 0.6V for silicon BJT in saturation mode. This misconception is >>>surprisingly common. >> >> Really? > >If you don't know how it works, the 0.6V answer seems very intuitive. > >> I recently did some saturation measurements on a BCX70 and was >> surprised myself... but at least I didn't expect 0.6. >> >> ftp://jjlarkin.lmi.net/BCX70_curves.pdf >> >> >> I bet few EEs know how to make an NPN saturate to exactly 0 volts. > >BJTs in perverted mode may saturate to few mV, but it won't be exactly zero. > > >Vladimir Vassilevsky >DSP and Mixed Signal Design Consultant >http://www.abvolt.com gnd | | | c V+----------b npn e | | signal If you adjust the base current by tweaking V+, you can ground the signal either side of zero volts.... for some transistors at least. I once, when I was a kid, designed a rack full of 16-bit DACs using such switches and an R-2R ladder made of hand-selected wirewound resistors. Each dac switch was... +10ref | | | c +--------b npn | e | | | | | +------- ladder resistor --+ | | | | | | | | e +--------b pnp c | | | -10ref I used trimpots to trim the base drive currents on the first four stages, for exactly zero switch offset. I think I used 2N3904 types, but it's been a while. The reference was derived from an ovenized Motorola reference zener that came in a handsome presentation-quality plastic tube with 1000-hour ageing graph and a number of genuine signatures. The dacs drove some sort of Dr Strangelove situation-room display thing for a missile defense center. 32 16-bit dacs in the rack cost something like $80K. John
From: Fred Bartoli on 14 May 2010 17:30
Vladimir Vassilevsky a �crit : > > > John Larkin wrote: >> On Fri, 14 May 2010 10:59:21 GMT, Jan Panteltje >> <pNaonStpealmtje(a)yahoo.com> wrote: >> >> >>> On a sunny day (Thu, 13 May 2010 17:48:41 -0700) it happened John Larkin >>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >>> <i37pu594178305v2a62vb99d263og1tfau(a)4ax.com>: >>> >>> >>>> I like this as a test: >>>> >>>> >>>> >>>> +10V >>>> | >>>> | >>>> | >>>> | >>>> c >>>> +5V--------------b >>>> e >>>> | >>>> | >>>> 1K >>>> | >>>> | >>>> | >>>> | >>>> gnd >>>> >>>> >>>> What's the base voltage? >>>> >>>> What's the base current? >>>> >>>> What's the emitter voltage? >>>> >>>> What's the collector current? >>>> >>>> What's the collector voltage? >>>> >>>> Any other comments? >>>> >>>> >>>> I'm not kidding. One "experienced ee" said that, since the transistor >>>> is saturated, the collector voltage is zero. A tech applicant said >>>> that the base voltage is 0.6. >>>> >>>> Some people got it right, but nobody has mentioned oscillation so far. >>>> >>>> John >>> >>> How many asked if it was germanium or Si? >>> Would be my first question. >> >> >> An interviewee could certainly ask questions, or mention assumptions. >> >> Can you still buy germanium transistors? Would that affect many of the >> answers much? > > You can buy germanium transistors in China if you need them. It is kinda > nostalgic to see old style metal cans. > Some SiGe fakes with no Si? -- Thanks, Fred. |