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allpass filters

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

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  1. 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. R1
    +----\/\/\-+
    | -\ |
    R1 | | \ |
    +-\/\/\+-|- \ |
    Vin ---+ | >--+--- Vout
    +-\/\/\+-|+ /
    C | | /
    | -/
    \
    / R2
    \
    |
    GROUND
     
  3. Sorry... I am not drunked!!! :)

    R1
    +----\/\/\-+
    | -\ |
    R1 | | \ |
    +-\/\/\+-|- \ |
    Vin ---+ | >--+--- Vout
    +--||--+-|+ /
    C | | /
    | -/
    \
    / R2
    \
    |
    GROUND
     
  4. Lord Garth

    Lord Garth Guest

    R1
    +----\/\/\-+
    | -\ |
    R1 | | \ |
    +-\/\/\+-|- \ |
    Vin ---+ | >--+--- Vout
    +---||-+-|+ /
    C | | /
    | -/
    \
    / R2
    \
    |
    GROUND
    R1
    +----\/\/\-+
    | -\ |
    R1 | | \ |
    +-\/\/\+-|- \ |
    Vin ---+ | >--+--- Vout
    +-\/\/\+-|+ /
    C | | /
    | -/
    \
    / R2
    \
    |
    GROUND
     
  5. Lord Garth

    Lord Garth Guest

    You beat me to it!
    R1
    +----\/\/\-+
    | -\ |
    R1 | | \ |
    +-\/\/\+-|- \ |
    Vin ---+ | >--+--- Vout
    +---||-+-|+ /
    C | | /
    | -/
    \
    / R2
    \
    |
    GROUND
    R1
    +----\/\/\-+
    | -\ |
    R1 | | \ |
    +-\/\/\+-|- \ |
    Vin ---+ | >--+--- Vout
    +-\/\/\+-|+ /
    C | | /
    | -/
    \
    / R2
    \
    |
    GROUND
     
  6. yep of 4 minutes!!!!!
    Did I win the answer? :)

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

    Lord Garth Guest

    yep of 4 minutes!!!!!
    Did I win the answer? :)


    Sorry, I don't know. :-(
     
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