Tauno Voipio  <tauno.voipio@notused.fi.invalid> wrote:

>There is no sense to simulate a Sallen-Key in the digital
>domain. There are better ways to implement the IIR filter.

Generally a digital filter with positive feedback would look
sort-of like a Sallen-Key, in some cases close to the same
topology.

It's not something I've ever chosen to do, however.

Steve

On 7.12.18 18:52, RichD wrote:
> On December 6, Rob Gaddi wrote:
>>> Reviewing some old stuff, I crossed the Sallen-Key filter.
>>> Analysis of this topology is relatively straightforward,
>>> but what I never sussed is the why - what makes it so
>>> important?   What was the great advance, at that time?
>>> And is it still considered so consequential, today?
>>
>> More an s.e.d question than comp.dsp, but I'm an analog guy so sure.
> 
> There's no digital equivalent?
> 
>> Sallen-Key gives you 2 poles (lowpass) per op-amp when you care about
>> op-amp costs, with fewer parts than an MFB and no inversion to worry
>> about
> 
> ?
> Don't know what MFB or inversion refers to.
> 
> --
> Rich


MFB: Multiple feedback.
Inversion: the output signal is inverted from the input.

There is no sense to simulate a Sallen-Key in the digital
domain. There are better ways to implement the IIR filter.

-- 

-TV

On December 6, Rob Gaddi wrote:
>> Reviewing some old stuff, I crossed the Sallen-Key filter.
>> Analysis of this topology is relatively straightforward,
>> but what I never sussed is the why - what makes it so
>> important?   What was the great advance, at that time?
>> And is it still considered so consequential, today?
>
> More an s.e.d question than comp.dsp, but I'm an analog guy so sure. 

There's no digital equivalent?

> Sallen-Key gives you 2 poles (lowpass) per op-amp when you care about 
> op-amp costs, with fewer parts than an MFB and no inversion to worry 
> about 

?
Don't know what MFB or inversion refers to.

--
Rich

On 12/6/18 10:25 AM, RichD wrote:
> Reviewing some old stuff, I crossed the Sallen-Key filter.
> Analysis of this topology is relatively straightforward,
> but what I never sussed is the why - what makes it so
> important?   What was the great advance, at that time?
> And is it still considered so consequential, today?
> 
> 
> --
> Rich
> 

More an s.e.d question than comp.dsp, but I'm an analog guy so sure. 
Sallen-Key gives you 2 poles (lowpass) per op-amp when you care about 
op-amp costs, with fewer parts than an MFB and no inversion to worry 
about (which can add yet more complication).  Plus, with no explicit 
gain, you get a gain of exactly 1 (less open-loop error), whereas with 
an MFB you have to buy expensive precision low tempco resistors to even 
approximate the same behavior.

Sallen-Key filters are my go-to workhorse filter topology.  They're what 
I use barring an active reason to use something else.

-- 
Rob Gaddi, Highland Technology -- www.highlandtechnology.com
Email address domain is currently out of order.  See above to fix.

Reviewing some old stuff, I crossed the Sallen-Key filter.  
Analysis of this topology is relatively straightforward, 
but what I never sussed is the why - what makes it so 
important?   What was the great advance, at that time?  
And is it still considered so consequential, today?


--
Rich