Re: Colpitts oscillators

On Tue, 08 Jan 2008 08:50:04 -0800, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

Joel Koltner wrote:
"Joerg" <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote in message
news:NxAgj.3190$jJ5.907@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
AoE isn't an RF book.

Yeah, but Colpitts oscillators are hardly an RF-only concept. I first had
them formally covered in some generic circuits class using Sedra & Smith...


Same here, they covered them in Basic Electrical Engineering for us, 1st
or 2nd semester. But let's face it, fresh grads coming out of
universities these days only see that weird component X1 in their
circuit, connected to two pins of their DSP, along with a couple of
capacitors that they have picked by rote from a table in the datasheet.
That's it. The most they might ever do in oscillator design is pick a
Fox can from the Digikey catalog. IME Clapp, Colpitts, Hartley and such
certainly fall into the RF (= weird) category for most engineers.


There are very few good RF books and IMHO the best are from the ham radio
community.

I wish more of them had a little more circuit theory behind them, as Hayward
does. Even DeMaw, who clearly knew what he was doing and was a better radio
designer than I'm likely to be any time soon :-), did an awful lot of hand
waving in some of his articles... (I don't have a copy of it to look at,
but I almost bet that I could tell you pretty quickly which parts of Solid
State Design for the Radio Amateur -- which he co-wrote with Hayward -- are
his vs. Hayward's...)


Sometimes I wonder who is going to write such books once others have
followed Doug and left the earth.


SPICE and theoretical approaches are fine but at the end of the day you'll
have to fire up the old Weller and experiment.

I don't mind firing up the, er, Metcal (hey, they're cheap at surplus!
...tips are only a buck each!) and doing so, although with that sort of
prototyping I usually feel constrained to just change component values
around and watch what happens. With a simulator you can make nice graphs
of, e.g., loop gain vs. frequency by opening the loop -- something pretty
difficult (well, time-consuming) to do on a bench.

Anything in particular you're planning to do with those BFP620's?


Probably the first thing is going to be a pulse amp. Got to be careful
though. Once Vce goes above 2.3V ... poof. An ever so slight overshoot
can send them off the cliff. OTOH it is incredible how cheap RF
transistors have become. IOW the good old days are right now.

Us old farts will always be employed ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

America: Land of the Free, Because of the Brave
.

Relevant Pages

  • Re: Colpitts oscillators
    ... but Colpitts oscillators are hardly an RF-only concept. ... But let's face it, fresh grads coming out of universities these days only see that weird component X1 in their circuit, connected to two pins of their DSP, along with a couple of capacitors that they have picked by rote from a table in the datasheet. ... The most they might ever do in oscillator design is pick a Fox can from the Digikey catalog. ... I thought this stuff was taught at the high school level and then that's it. ...
    (sci.electronics.design)
  • Re: Different strokes for different folks
    ... _Crystal Oscillator Circuits_ by Matthys, regarding Colpitts oscillators: "Physically, the circuit is very simple, but analytically it is very complex." ... _Practical RF Circuit Design for Modern Wireless Systems_ by Besser & Gilmore: "The analysis of a Colpitts oscillator is very simple." ...
    (sci.electronics.design)
  • Re: Colpitts oscillators
    ... Same here, they covered them in Basic Electrical Engineering for us, 1st or 2nd semester. ... But let's face it, fresh grads coming out of universities these days only see that weird component X1 in their circuit, connected to two pins of their DSP, along with a couple of capacitors that they have picked by rote from a table in the datasheet. ... The most they might ever do in oscillator design is pick a Fox can from the Digikey catalog. ... With a simulator you can make nice graphs of, e.g., loop gain vs. frequency by opening the loop -- something pretty difficult to do on a bench. ...
    (sci.electronics.design)
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