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From: Power boy on 21 Mar 2010 11:07
On Mar 21, 9:15 am, Mark <makol...(a)yahoo.com> wrote:
> On Mar 20, 10:58 pm, Power boy <bigca...(a)gmail.com> wrote:
>
>
>
> > On Mar 19, 5:55 pm, whit3rd <whit...(a)gmail.com> wrote:
>
> > > On Mar 18, 9:24 pm, Power boy <bigca...(a)gmail.com> wrote:
>
> > > > I am thinking over current source again in this year. Previously I did
> > > > current source but I never got into the RF field.
>
> > > > I am wondering how to design a constant power current source with a
> > > > modulation frequency from DC to 150 MHz?
> > > > Right now suppose I need 0 to 1A with 0-150MHz analogue modulation,
> > > > how to do it?
>
> > > An emitter-coupled pair with current source on the emitters (an
> > > inductor,
> > > at high frequency) will steer current effectively, and 1A/150 MHz
> > > is not out of the question.   You won't like the results if you insist
> > > on '0' in the range, that gets into hard base-drive requirements (but
> > > you could always leave the transistor turned ON and steal some
> > > current...).
>
> > > Doesn't need to be bipolar, of course, a source-coupled pair of
> > > MOSFETs could do something similar.
>
> > > I'm dubious that the output impedance will be high enough to be
> > > 'practically infinite', like a good DC current source.
>
> > it seems working on open loop only.
> > the feedback is a big issue, at @150MHz need to do feedback to keep
> > constant power output.
>
> "constant power" and "current source" are contradictory.
> You can have one or the other but not both.
> Which do you want?
> Mark
my misleading, this power is not V*I.
current source could be constant power , this power is from the driven
object like a laser diode, this power is from the light emission and
detected by a photodiode.
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