+ Post New Thread
Results 1 to 4 of 4
  1. #1
    Member level 3
    Points: 659, Level: 5

    Join Date
    Jan 2018
    Posts
    64
    Helped
    2 / 2
    Points
    659
    Level
    5

    Resistors in Wilson current mirror

    I have some questions concerning analog audio amplifiers: what is the purpose of resistors R1 and R2 in the Wilson current mirror? With what formula are they calculated? Can they be omitted? If they are omitted, what happens to the VAS (Voltage Amplifier Stage)?

    Click image for larger version. 

Name:	Screenshot (1).png 
Views:	0 
Size:	6.1 KB 
ID:	156464

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 5
    Points: 40,234, Level: 49

    Join Date
    Mar 2008
    Location
    USA
    Posts
    6,494
    Helped
    1903 / 1903
    Points
    40,234
    Level
    49

    Re: Resistors in Wilson current mirror

    They improve Vbe-match and current-match fidelity (if
    the resistors have better matching tolerance than the
    transistors' Vbe). You need to establish a current across
    the resistors which dwarfs the mismatch voltage (like,
    if transistor population has a +/-10mV Vbe scatter,
    setting a 100mV (Iset*R) value ought to improve the
    mismatch 90%.

    You lose a little headroom but in older +/-15V analog
    (or discrete) this is tolerable.

    An audio circuit doesn't care about DC as long as
    it's centered and linear, right? If there's feedback
    then small mismatch error in current mirrors may not
    amount to anything. You'd need mismatch modeled
    to say.


    1 members found this post helpful.

    •   AltAdvertisement

        
       

  3. #3
    Super Moderator
    Points: 261,937, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    45,781
    Helped
    13913 / 13913
    Points
    261,937
    Level
    100

    Re: Resistors in Wilson current mirror

    Current mirror need monolithic transistor pairs to achieve reasonable matching. The emitter degeneration resistors are a possible means to get a kind of current mirror behavior with discrete transistors.


    1 members found this post helpful.

    •   AltAdvertisement

        
       

  4. #4
    Advanced Member level 5
    Points: 30,746, Level: 42
    BigBoss's Avatar
    Join Date
    Nov 2001
    Location
    Turkey
    Posts
    4,509
    Helped
    1359 / 1359
    Points
    30,746
    Level
    42

    Re: Resistors in Wilson current mirror

    They can also be used to achieve PTAT Current by well adjusting Resistor and Transistor Multiplication number..


    1 members found this post helpful.

--[[ ]]--