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From: Joel Koltner on 26 Jul 2010 21:06
"Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in
message news:jl9s465bifaopu6ocv3q6ehdirubc3295m(a)4ax.com...
> All-pass:
>
>
> Vin ___ Vout
> o-----|___|---o---o
> |
> |
> ---
> ---
> |
> |
> o
> -Vin
>
> Get -VIN (180� with an inverting OpAmp)

Gee, and I thought my "use an RC and a CR and then subtract" was vaguely
clever -- here you're doing it via superposition, effectively. Very slick.

Although you presumably have to worry about the source impedance of Vin being
rather lower than the resistor's for this to work well...

---Joel

From: john1987 on 26 Jul 2010 21:12
Hello,

Thanks for the suggestions. Would you please explain a little more
that how can I implement all pass filter. I am unable to understand
the diagram that you sent me? Plus if I choose to go with the low pass
than I am still unable to undertsand that how will I pick the resistor
value.


John
From: Jim Thompson on 26 Jul 2010 21:52
On Mon, 26 Jul 2010 18:06:43 -0700, "Joel Koltner"
<zapwireDASHgroups(a)yahoo.com> wrote:

>"Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in
>message news:jl9s465bifaopu6ocv3q6ehdirubc3295m(a)4ax.com...
>> All-pass:
>>
>>
>> Vin ___ Vout
>> o-----|___|---o---o
>> |
>> |
>> ---
>> ---
>> |
>> |
>> o
>> -Vin
>>
>> Get -VIN (180� with an inverting OpAmp)
>
>Gee, and I thought my "use an RC and a CR and then subtract" was vaguely
>clever -- here you're doing it via superposition, effectively. Very slick.
>
>Although you presumably have to worry about the source impedance of Vin being
>rather lower than the resistor's for this to work well...
>
>---Joel

Naaaah! In the GPS, it's PECL followers.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Spice is like a sports car...
Performance only as good as the person behind the wheel.
From: Joel Koltner on 26 Jul 2010 22:41
"john1987" <conphiloso(a)hotmail.com> wrote in message
news:38b7b9a7-4fb0-468b-b9d6-5d0ddd7a35cb(a)z10g2000yqb.googlegroups.com...
> Thanks for the suggestions. Would you please explain a little more
> that how can I implement all pass filter. I am unable to understand
> the diagram that you sent me?

The rectangular box in his diagram there is the resistor.

> Plus if I choose to go with the low pass
> than I am still unable to undertsand that how will I pick the resistor
> value.

You pick the resistor value based off of setting 1/(2*pi*R*C) to be the
frequency you're interested in obtaining a 90 degree phase shift at and
solving for R. Pick a "reasonable" value for C -- e.g., 1uF or so -- and then
calculate R... if it's <100ohms or >100kohms ("reasonable" resistor values),
change your capacitor's value to compensate.

People are likely ignoring you a bit here since this sounds suspiciously like
a homework problem. If it is, and if you use Jim's method there (and please
actually understand how it works), your instructors should be impressed.

(Granted, in the real world you might not have "-Vin" readily available, so
you might want to come up with the "textbook" solution as well in case they're
picky and there are unstated restrictions to the problem... such as, "your
answer must match the one the professor is expecting." :-) )

Go download a copy of LTspice and verify your solution if you're a little
unsure of yourself.

---Joel

From: George Herold on 26 Jul 2010 23:02
On Jul 26, 9:12 pm, john1987 <conphil...(a)hotmail.com> wrote:
> Hello,
>
> Thanks for the suggestions. Would you please explain a little more
> that how can I implement all pass filter. I am unable to understand
> the diagram that you sent me? Plus if I choose to go with the low pass
> than I am still unable to undertsand that how will I pick the resistor
> value.
>
> John

John1987, my suggestion is that you stick with the two series low
passes. I think you understand it. 10k ohms is a good starting
resistor value for a lot of opamp circuits. Calculate what C you
need and go on from there.

George H.

Google "all pass filter" and opamp if you want to go that way.
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