[sdiy] Passive filters and impedances

[Gordonjcp]

On Thu, Nov 05, 2015 at 01:48:08PM +0100, Mattias Rickardsson wrote:
> On 4 November 2015 at 22:16, Richie Burnett
> <rburnett at richieburnett.co.uk> wrote:
> >> Anyway - has this impedance scaling technique ever been used to full
> >> extent in any ladder filters, using different capacitor values for all
> >> stages?
> >
> > You mean used in diode or transistor ladders?  I suspect not, as usually all
> > of the diodes or transistors operate at the same bias current, and would
> > therefore exhibit *the same* incremental resistance.  Not a decade apart.
> 
> Perhaps double diodes could be used in series or parallel to get
> double or half the resistance. Not a decade apart, but better than
> nothing? :-)

Aha, the voltage drop of the diodes is not down to actual "resistance" though so they don't behave in parallel the way that a variable resistor would.

-- 
Gordonjcp MM0YEQ