What kind of analog circuit has a bad group delay spec?

Hi,

I was asked by someone about this question: 
"What kind of analog circuit has a bad group delay spec?"

I only know some analog circuit having good group delay spec,
not the opposite.


Do you know the answer?

Thanks,

fl  <rxjwg98@gmail.com> wrote:

>I was asked by someone about this question: 
>"What kind of analog circuit has a bad group delay spec?"

There are no stupid questions, only stupid answers, although this
question comes close.  

A bad spec would be either:

1) A spec that is impossible to meet, or is economically infeasible; or

2) A spec that, if met, would cause the surrounding system to
malfunction; or

3) A spec that is self-contradictory 

A bad group delay spec would be a group delay spec that is bad per
one of the above.

Now I need more coffee.

Steve

On Tue, 28 Mar 2017 12:09:42 -0700, fl wrote:

> Hi,
> 
> I was asked by someone about this question:
> "What kind of analog circuit has a bad group delay spec?"
> 
> I only know some analog circuit having good group delay spec,
> not the opposite.
> 
> 
> Do you know the answer?
> 
> Thanks,

It sounds like a poorly thought out interview question, or one of those 
where they're trying to pin you to the wall so they can measure how you 
squirm.

Assuming that "bad" means "spread out", any minimum-phase filter that has 
a good sharp cutoff in the frequency domain (particularly one with 
ripple) will have a "bad" group delay characteristic, at least in the 
sense that the group delay will be spread out.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

On 03/28/2017 12:09 PM, fl wrote:
> Hi,
>
> I was asked by someone about this question:
> "What kind of analog circuit has a bad group delay spec?"
>
> I only know some analog circuit having good group delay spec,
> not the opposite.
>
>
> Do you know the answer?
>
> Thanks,
>

An open circuit.  The signal never gets there at all; that's about the 
worst group delay you can ask for.

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

On 2017-03-28 21:27, Rob Gaddi wrote:
> On 03/28/2017 12:09 PM, fl wrote:
>> Hi,
>>
>> I was asked by someone about this question:
>> "What kind of analog circuit has a bad group delay spec?"
>>
>> I only know some analog circuit having good group delay spec,
>> not the opposite.
>>
>>
>> Do you know the answer?
>>
>> Thanks,
>>
> 
> An open circuit.  The signal never gets there at all; that's about the
> worst group delay you can ask for.
> 

Ah, and the best is a grounded circuit. The
signal get there as fast as it could be... :-)

bye,

-- 

piergiorgio

On 3/28/17 3:09 PM, fl wrote:
> Hi,
>
> I was asked by someone about this question:
> "What kind of analog circuit has a bad group delay spec?"
>
> I only know some analog circuit having good group delay spec,
> not the opposite.
>
>
> Do you know the answer?
>
> Thanks,

well, "good" and "bad" is in the eye of the beholder.

and "spec" is whatever they say you gotta do.  it might be a "hard spec" 
or an "easy spec".

in terms of group delay and analog *filter* circuits, like the 
Sallen-Key, i would say that a 6th-order (3 cascaded Sallen-Key 
circuits) Type 1 Chebyshev filter has crappy ("bad" can be someone 
else's description) group delay *performance*.  an elliptic filter is 
worse (but has zeros, so a Sallen-Key is not the right circuit for it 
and i would have to look up the name of a good 2nd-order circuit with 2 
poles and 2 zeros).


-- 

r b-j                  rbj@audioimagination.com

"Imagination is more important than knowledge."

On Tue, 28 Mar 2017 12:09:42 -0700, fl wrote:

> Hi,
> 
> I was asked by someone about this question: 
> "What kind of analog circuit has a bad group delay spec?"
> 
> I only know some analog circuit having good group delay spec,
> not the opposite.
> 
> 
> Do you know the answer?
> 
> Thanks,

Curious that the question is about an analog circuit (hardware),
yet they're asking about a spec (design goal).

So, either something that is in some sense broken, or perhaps
can't _meet_ the spec (has high sensitivity to parameters).  If
they're actually asking for something with a near-constant group
delay - there are numerous other choices (I'd start with an all
pass filter).

The good thing about ambiguous questions is that you can almost
never be completely wrong.

Frank Miles  <fpm@u.washington.edu> wrote:

>On Tue, 28 Mar 2017 12:09:42 -0700, fl wrote:

>> "What kind of analog circuit has a bad group delay spec?"

>Curious that the question is about an analog circuit (hardware),
>yet they're asking about a spec (design goal).

It could be some category of analog circuits has or had bad group
delay specs.  Say, late-90's ceramic filters in 802.11 radios.
(Which were poorly specified since they had too much delay spread,
although what I really suspect is, they were underspecified.)

So that's one example.

Steve

If you read the question carefully it sounds like a joke question that the OP took seriously. Probably a "bonus" question on an exam. The answer is probably a "Slowpass Filter". 

Bob

On Sat, 1 Apr 2017 01:01:37 -0700 (PDT), radams2000@gmail.com wrote:

>If you read the question carefully it sounds like a joke question that the OP took seriously. Probably a "bonus" question on an exam. The answer is probably a "Slowpass Filter". 
>
>Bob

Perfect for April 1!



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