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Transistor oscillator.

Started by Ian Field January 13, 2016
Is there a rock bottom oscillator that will free run at the frequency limit 
of whatever transistor is put in it?

I was thinking of the common base job with a capacitor strapped from 
collector to emitter, but am unsure what to use as a collector load.

Basically for testing how good are a collection of vintage germanium 
transistors.

Thanks for any help.
 

On Wed, 13 Jan 2016 22:21:40 -0000
"Ian Field" <gangprobing.alien@ntlworld.com> wrote:

> Is there a rock bottom oscillator that will free run at the frequency > limit of whatever transistor is put in it? > > I was thinking of the common base job with a capacitor strapped from > collector to emitter, but am unsure what to use as a collector load. > > Basically for testing how good are a collection of vintage germanium > transistors. > > Thanks for any help. > >
This article... https://en.wikipedia.org/wiki/Blocking_oscillator doesn't give a relationship between transistor parameters and switching frequency, but then it's not a common-base circuit they use. joe
On Wed, 13 Jan 2016 22:21:40 +0000, Ian Field wrote:

> Is there a rock bottom oscillator that will free run at the frequency > limit of whatever transistor is put in it? > > I was thinking of the common base job with a capacitor strapped from > collector to emitter, but am unsure what to use as a collector load. > > Basically for testing how good are a collection of vintage germanium > transistors. > > Thanks for any help.
What frequency limit do you mean? For most uses the rule of thumb is probably Ft/100, but there are some radio applications that push that to Ft/10, and at one point in the 70's, I am told, (and maybe still, for all I know) there were microwave applications that considered a transistor "useful" at any frequency where it had power gain was considered useful, and that frequency could actually be above Ft. My first thought would be to build a circuit that automagically finds the point where the phase shift in the current gain is 90 degrees. Since you have modern electronics to draw on for your test circuit, make some high- impedance source to pump current into the transistor base, put a really small collector impedance on it and amplify the snot out of it, then find the point of 90 degrees phase shift. -- www.wescottdesign.com
On Wednesday, January 13, 2016 at 2:21:16 PM UTC-8, Ian Field wrote:
> Is there a rock bottom oscillator that will free run at the frequency limit > of whatever transistor is put in it?
Sure, it's common to test a new fabrication recipe for transistors with a ring oscillator. Three or more (odd number) of inverters, negative feedback connected in cascade (series) (which is why it has to be an odd number).
> Basically for testing how good are a collection of vintage germanium > transistors.
Oh, you'd have to modify the scheme for non-identical units. And, it's intended for biased inverting amplifiers (so depends somewhat on resistor values).
On Wednesday, January 13, 2016 at 5:21:16 PM UTC-5, Ian Field wrote:
> Is there a rock bottom oscillator that will free run at the frequency limit > of whatever transistor is put in it? > > I was thinking of the common base job with a capacitor strapped from > collector to emitter, but am unsure what to use as a collector load. > > Basically for testing how good are a collection of vintage germanium > transistors. > > Thanks for any help.
Hi, An interesting question, but very vague. An oscillator is defined by its oscillation frequency, and if a transistor is operated at its frequency limit, then one would have to find a transistor whose frequency limit is the same as your frequency of interest. Also, your suggestion of a capacitor connected to the base sounds more like a "Joule thief" design, a very inefficient one.
On Thursday, January 14, 2016 at 12:42:07 AM UTC-5, whit3rd wrote:
> On Wednesday, January 13, 2016 at 2:21:16 PM UTC-8, Ian Field wrote: > > Is there a rock bottom oscillator that will free run at the frequency limit > > of whatever transistor is put in it? > > Sure, it's common to test a new fabrication recipe for transistors with > a ring oscillator. Three or more (odd number) of inverters, negative feedback > connected in cascade (series) (which is why it has to be an odd number).
A ring oscillator is not a very useful circuit anyway -- I have never seen a practical circuit triggered by a ring oscillator.
> > > Basically for testing how good are a collection of vintage germanium > > transistors. > > Oh, you'd have to modify the scheme for non-identical units. > And, it's intended for biased inverting amplifiers (so depends somewhat > on resistor values).
On Wednesday, January 13, 2016 at 11:12:27 PM UTC-8, daku...@gmail.com wrote:
> On Thursday, January 14, 2016 at 12:42:07 AM UTC-5, whit3rd wrote: > > On Wednesday, January 13, 2016 at 2:21:16 PM UTC-8, Ian Field wrote: > > > Is there a rock bottom oscillator that will free run at the frequency limit > > > of whatever transistor is put in it? > > > > Sure, it's common to test a new fabrication recipe for transistors with > > a ring oscillator. Three or more (odd number) of inverters, negative feedback > > connected in cascade (series) (which is why it has to be an odd number).
> A ring oscillator is not a very useful circuit anyway -- I have never seen a practical circuit > triggered by a ring oscillator.
For good reasons: an inverter in a ring oscillator doesn't necessarily execute a full logic swing, it doesn't have a load similar to a working gate, nor any external wiring (if the ring oscillator is an on-chip construction in an integrated circuit). It does, however, run at a high frequency set by internal delays and gain-versus-frequency of the individual stages. Barkhausen's criterion gives you a good handle on the stage delays at unity power gain, being t_stage_delay = period/(2 * N)
On Wed, 13 Jan 2016 23:12:14 -0800 (PST), dakupoto@gmail.com wrote:

[snip]
>A ring oscillator is not a very useful circuit anyway -- I have never seen a practical circuit >triggered by a ring oscillator. >>
[snip] I have made VCO's from ring oscillators, just vary VDD,VSS ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Wednesday, January 13, 2016 at 5:21:16 PM UTC-5, Ian Field wrote:
> Is there a rock bottom oscillator that will free run at the frequency limit > of whatever transistor is put in it? > > I was thinking of the common base job with a capacitor strapped from > collector to emitter, but am unsure what to use as a collector load. > > Basically for testing how good are a collection of vintage germanium > transistors.
Maybe build a single gain stage with a socket for the transistor, and look at where the gain rolls off...? George H.
> > Thanks for any help.
Maybe build a single gain stage with a socket

"Joe Hey" <joehey@mailinator.com> wrote in message 
news:20160114004016.4b10a9d8.joehey@mailinator.com...
> On Wed, 13 Jan 2016 22:21:40 -0000 > "Ian Field" <gangprobing.alien@ntlworld.com> wrote: > >> Is there a rock bottom oscillator that will free run at the frequency >> limit of whatever transistor is put in it? >> >> I was thinking of the common base job with a capacitor strapped from >> collector to emitter, but am unsure what to use as a collector load. >> >> Basically for testing how good are a collection of vintage germanium >> transistors. >> >> Thanks for any help. >> >> > > This article... > > https://en.wikipedia.org/wiki/Blocking_oscillator > > doesn't give a relationship between transistor parameters and switching > frequency, but then it's not a common-base circuit they use.
AFAICR: the blocking oscillator period is determined by the time it takes the core to saturate - not how fast the transistor can go.