# allpass filters

Discussion in 'Electronic Basics' started by Alessandro Esposito, Nov 10, 2003.

1. ### Alessandro EspositoGuest

HI need to shift the phase of a signal between 0 to 180°. I usually work
with sinuswave between 10KHk and 100MHz.
I found out it is possbile to build a so called allpass filter to make this:

R1
+----\/\/\-+
| -\ |
R1 | | \ |
+-\/\/\+-|- \ |
Vin ---+ | >--+--- Vout
+-\/\/\+-|+ /
C | | /
| -/
\
/ R2
\
|
GROUND

in which R2 is variable and control the phase delay.

I have to question:

1) I do not have formulas to setup the values of C and Ri... is, for
example, R1 the input impedence of the circuit?
2) Is it possible to use this circuit up to 100MHz? Which opamp could work?

A less important aspect:
I would like to modify this phase via a PC: Do you think is is reliable the
use of a DAC to control the voltage on a FET base to use it instead (or
with) R2?

Thanks
Alessandro

2. ### Alessandro EspositoGuest

R1
+----\/\/\-+
| -\ |
R1 | | \ |
+-\/\/\+-|- \ |
Vin ---+ | >--+--- Vout
+-\/\/\+-|+ /
C | | /
| -/
\
/ R2
\
|
GROUND

3. ### Alessandro EspositoGuest

Sorry... I am not drunked!!!

R1
+----\/\/\-+
| -\ |
R1 | | \ |
+-\/\/\+-|- \ |
Vin ---+ | >--+--- Vout
+--||--+-|+ /
C | | /
| -/
\
/ R2
\
|
GROUND

4. ### Lord GarthGuest

R1
+----\/\/\-+
| -\ |
R1 | | \ |
+-\/\/\+-|- \ |
Vin ---+ | >--+--- Vout
+---||-+-|+ /
C | | /
| -/
\
/ R2
\
|
GROUND
R1
+----\/\/\-+
| -\ |
R1 | | \ |
+-\/\/\+-|- \ |
Vin ---+ | >--+--- Vout
+-\/\/\+-|+ /
C | | /
| -/
\
/ R2
\
|
GROUND

5. ### Lord GarthGuest

You beat me to it!
R1
+----\/\/\-+
| -\ |
R1 | | \ |
+-\/\/\+-|- \ |
Vin ---+ | >--+--- Vout
+---||-+-|+ /
C | | /
| -/
\
/ R2
\
|
GROUND
R1
+----\/\/\-+
| -\ |
R1 | | \ |
+-\/\/\+-|- \ |
Vin ---+ | >--+--- Vout
+-\/\/\+-|+ /
C | | /
| -/
\
/ R2
\
|
GROUND

6. ### Alessandro EspositoGuest

yep of 4 minutes!!!!!

You beat me to it!
R1
+----\/\/\-+
| -\ |
R1 | | \ |
+-\/\/\+-|- \ |
Vin ---+ | >--+--- Vout
+---||-+-|+ /
C | | /
| -/
\
/ R2
\
|
GROUND
R1
+----\/\/\-+
| -\ |
R1 | | \ |
+-\/\/\+-|- \ |
Vin ---+ | >--+--- Vout
+-\/\/\+-|+ /
C | | /
| -/
\
/ R2
\
|
GROUND

7. ### Lord GarthGuest

yep of 4 minutes!!!!!