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From: oopere on 19 Mar 2010 11:19


Candide Voltaire wrote:
> On Mar 19, 9:21 am, oopere <m...(a)somewhere.net> wrote:
>> Candide Voltaire wrote:
>>> I'm looking for a passive rc-network which produces a delay of 200ns
>>> for a 5MHz sinusoidal voltage.
>>> Which is the minimum number of RCs to achieve this? Are there some
>>> schematics optimized for this purpose?
>>> Candide
>> Since the required delay is a whole period, the answer is yes, there is
>> an optimum schematic, although it is a degenerate case of RC, with R=0,
>> C=0 (inexpensive)
>>
>> Vin----R--�--Vout
>> |
>> C
>> |
>> gnd
>>
>> Pere
>
> OK that's correct, do you also have an answer in case we want 180ns?
>
> Candide

A passive RC network will not exhibit constant amplification over
frequency. This means that you can not say that it is a pure delay.
Having said that, a single RC section is able to produce -90 deg of
phase shift. Two cascaded RC sections will give you an all pole second
order response able to produce up to -180 deg, and so on. If you require
180ns (-324 deg), you would need 4 sections.

But you need to tell more about your problem. What is the intended
application? Do you really need a pure delay? Does it really need to be
RC-only? What signal levels are involved?

Pere
From: oopere on 19 Mar 2010 11:20


Jan Panteltje wrote:
> On a sunny day (Fri, 19 Mar 2010 09:21:13 +0100) it happened oopere
> <me(a)somewhere.net> wrote in <hnvc5q$a5u$1(a)defalla.upc.es>:
>
>> Candide Voltaire wrote:
>>> I'm looking for a passive rc-network which produces a delay of 200ns
>>> for a 5MHz sinusoidal voltage.
>>> Which is the minimum number of RCs to achieve this? Are there some
>>> schematics optimized for this purpose?
>>>
>>>
>>> Candide
>> Since the required delay is a whole period, the answer is yes, there is
>> an optimum schematic, although it is a degenerate case of RC, with R=0,
>> C=0 (inexpensive)
>>
>> Vin----R--�--Vout
>> |
>> C
>> |
>> gnd
>>
>> Pere
>
> Na, C=0 and R=0 is extremely expensive.
> Impossible to make even.
> Better just use some meters of coax cable to delay one period :-)

But that's not a passive rc circuit ;)
From: John Larkin on 19 Mar 2010 11:30
On Fri, 19 Mar 2010 16:19:17 +0100, oopere <me(a)somewhere.net> wrote:

>
>
>Candide Voltaire wrote:
>> On Mar 19, 9:21 am, oopere <m...(a)somewhere.net> wrote:
>>> Candide Voltaire wrote:
>>>> I'm looking for a passive rc-network which produces a delay of 200ns
>>>> for a 5MHz sinusoidal voltage.
>>>> Which is the minimum number of RCs to achieve this? Are there some
>>>> schematics optimized for this purpose?
>>>> Candide
>>> Since the required delay is a whole period, the answer is yes, there is
>>> an optimum schematic, although it is a degenerate case of RC, with R=0,
>>> C=0 (inexpensive)
>>>
>>> Vin----R--�--Vout
>>> |
>>> C
>>> |
>>> gnd
>>>
>>> Pere
>>
>> OK that's correct, do you also have an answer in case we want 180ns?
>>
>> Candide
>
>A passive RC network will not exhibit constant amplification over
>frequency. This means that you can not say that it is a pure delay.
>Having said that, a single RC section is able to produce -90 deg of
>phase shift.

but with an output amplitude of zero.


John

From: Jan Panteltje on 19 Mar 2010 12:23
On a sunny day (Fri, 19 Mar 2010 16:20:08 +0100) it happened oopere
<me(a)somewhere.net> wrote in <ho04n9$d9l$2(a)defalla.upc.es>:

>
>
>Jan Panteltje wrote:
>> On a sunny day (Fri, 19 Mar 2010 09:21:13 +0100) it happened oopere
>> <me(a)somewhere.net> wrote in <hnvc5q$a5u$1(a)defalla.upc.es>:
>>
>>> Candide Voltaire wrote:
>>>> I'm looking for a passive rc-network which produces a delay of 200ns
>>>> for a 5MHz sinusoidal voltage.
>>>> Which is the minimum number of RCs to achieve this? Are there some
>>>> schematics optimized for this purpose?
>>>>
>>>>
>>>> Candide
>>> Since the required delay is a whole period, the answer is yes, there is
>>> an optimum schematic, although it is a degenerate case of RC, with R=0,
>>> C=0 (inexpensive)
>>>
>>> Vin----R--�--Vout
>>> |
>>> C
>>> |
>>> gnd
>>>
>>> Pere
>>
>> Na, C=0 and R=0 is extremely expensive.
>> Impossible to make even.
>> Better just use some meters of coax cable to delay one period :-)
>
>But that's not a passive rc circuit ;)

But it is: a cable has a capacitance and resistance.
The inductance comes for free, and makes it possible :-)
And the cable method WORKS.


From: oopere on 19 Mar 2010 12:50
John Larkin wrote:
> On Fri, 19 Mar 2010 16:19:17 +0100, oopere <me(a)somewhere.net> wrote:
>
>>
>> Candide Voltaire wrote:
>>> On Mar 19, 9:21 am, oopere <m...(a)somewhere.net> wrote:
>>>> Candide Voltaire wrote:
>>>>> I'm looking for a passive rc-network which produces a delay of 200ns
>>>>> for a 5MHz sinusoidal voltage.
>>>>> Which is the minimum number of RCs to achieve this? Are there some
>>>>> schematics optimized for this purpose?
>>>>> Candide
>>>> Since the required delay is a whole period, the answer is yes, there is
>>>> an optimum schematic, although it is a degenerate case of RC, with R=0,
>>>> C=0 (inexpensive)
>>>>
>>>> Vin----R--�--Vout
>>>> |
>>>> C
>>>> |
>>>> gnd
>>>>
>>>> Pere
>>> OK that's correct, do you also have an answer in case we want 180ns?
>>>
>>> Candide
>> A passive RC network will not exhibit constant amplification over
>> frequency. This means that you can not say that it is a pure delay.
>> Having said that, a single RC section is able to produce -90 deg of
>> phase shift.
>
> but with an output amplitude of zero.
>
>
> John
>

That's just a second order side effect :)

Pere
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