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From: Jim Thompson on 26 Jul 2010 20:25
On Mon, 26 Jul 2010 17:16:23 -0700, Tim Wescott <tim(a)seemywebsite.com>
wrote:

>On 07/26/2010 05:09 PM, john1987 wrote:
>> Hi,
>>
>> Did you mean Cascade two RC circuits together one after another?
>> please explain !
>>
>
> Vin ___ ___ Vout
> o-----|___|---o---|___|----o------o
> | |
> | |
> --- ---
> --- ---
> | |
> | |
> === ===
> GND GND
>(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

All-pass:


Vin ___ Vout
o-----|___|---o---o
|
|
---
---
|
|
o
-Vin

Get -VIN (180� with an inverting OpAmp)

And no loss of amplitude.

...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...
Only as good as the person behind the wheel.
From: john1987 on 26 Jul 2010 20:26
Hi,

High pass or cascading schemes. The other problem is that how should I
chose the value of R for both cascading and non cascading because the
load is an opamp with very high input impedance.


Thanks

John
From: Tim Wescott on 26 Jul 2010 20:35
On 07/26/2010 05:25 PM, Jim Thompson wrote:
> On Mon, 26 Jul 2010 17:16:23 -0700, Tim Wescott<tim(a)seemywebsite.com>
> wrote:
>
>> On 07/26/2010 05:09 PM, john1987 wrote:
>>> Hi,
>>>
>>> Did you mean Cascade two RC circuits together one after another?
>>> please explain !
>>>
>>
>> Vin ___ ___ Vout
>> o-----|___|---o---|___|----o------o
>> | |
>> | |
>> --- ---
>> --- ---
>> | |
>> | |
>> === ===
>> GND GND
>> (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
>
> All-pass:
>
>
> Vin ___ Vout
> o-----|___|---o---o
> |
> |
> ---
> ---
> |
> |
> o
> -Vin
>
> Get -VIN (180� with an inverting OpAmp)
>
> And no loss of amplitude.

Kewl. If Vout needs buffering it'll use an extra op-amp, but still neato.

--

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

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
From: Jim Thompson on 26 Jul 2010 20:58
On Mon, 26 Jul 2010 17:35:13 -0700, Tim Wescott <tim(a)seemywebsite.com>
wrote:

>On 07/26/2010 05:25 PM, Jim Thompson wrote:
>> On Mon, 26 Jul 2010 17:16:23 -0700, Tim Wescott<tim(a)seemywebsite.com>
>> wrote:
>>
>>> On 07/26/2010 05:09 PM, john1987 wrote:
>>>> Hi,
>>>>
>>>> Did you mean Cascade two RC circuits together one after another?
>>>> please explain !
>>>>
>>>
>>> Vin ___ ___ Vout
>>> o-----|___|---o---|___|----o------o
>>> | |
>>> | |
>>> --- ---
>>> --- ---
>>> | |
>>> | |
>>> === ===
>>> GND GND
>>> (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
>>
>> All-pass:
>>
>>
>> Vin ___ Vout
>> o-----|___|---o---o
>> |
>> |
>> ---
>> ---
>> |
>> |
>> o
>> -Vin
>>
>> Get -VIN (180� with an inverting OpAmp)
>>
>> And no loss of amplitude.
>
>Kewl. If Vout needs buffering it'll use an extra op-amp, but still neato.

I didn't invent that. Not sure where I picked it up. But I've been
using that scheme...two of them staggered to maintain 90� differential
over about an octave (for image reject mixers/LO's), ever since my
first GPS chip... over 20 years ago.

...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 21:02
"Tim Wescott" <tim(a)seemywebsite.com> wrote in message
news:19SdnXAXQNtav9PRnZ2dnUVZ_gqdnZ2d(a)web-ster.com...
> Cascade an RC and you'll get 90 degrees at f = 1/(2*pi*R*C), with a signal
> strength that's only been attenuated 3:1. Put that into the + end of a
> voltage buffer or positive-gain op-amp and you'll be fine.

Another approach might be to use an RC and a CR filter -- providing -45 and
+45 degree phase shifts -- and then let the op-amp subtract one from the
other, giving you 90 degrees total.

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