[sdiy] Passive filters and impedances

[Phil Macphail]

An alternative that could be easier to get started with would be to use a series of ABCD matrices. That way you can solve for any number of stages too. 

Phil

Sent from my iPhone

> On 31 Oct 2015, at 20:02, Donald Tillman <don at till.com> wrote:
> 
> 
>> On Oct 31, 2015, at 9:24 AM, Tom Wiltshire <tom at electricdruid.net> wrote:
>> 
>>    http://electricdruid.net/images/PassiveFilters.png
> 
> Yikes!  It would be a lot nicer to just draw the schematic on paper and scan that.  :-)
> 
> 
>> For the first order case, I've been able to derive the transfer function by thinking of it as a potential divider with impedances.
> 
> Yes, that works fine.
> 
>> However, I can't make the second order (or by extension third order) case work the same way.
> 
> Right.  It gets messy, error prone, and unsolvable.
> 
> To analyse a non-trivial circuit you need to label the N nodes, know that the current summed into each node must be zero (because "what comes in must go out"), write out an equation for the current into each node in terms of its neighboring voltages, and solve the N simultaneous equations.
> 
> Like many techniques, there's a barrier to entry, but after that it becomes really efficient.
> 
>  -- Don
> 
> --
> Don Tillman
> Palo Alto, California
> don at till.com
> http://www.till.com
> 
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