+ Post New Thread
Results 1 to 3 of 3
  1. #1
    Junior Member level 2
    Points: 138, Level: 1

    Join Date
    Feb 2019
    Posts
    20
    Helped
    0 / 0
    Points
    138
    Level
    1

    Stable Vbias for Current source load/ Current Mirros

    1 Why do we need a stable Vbias for current source load ?
    2 Why can not we use a simple resistive network to bias a lets say for example NMOS current source load ?
    3 Why do we need current Mirrors ?
    4 Why do we use Bandgap reference to generate the Vbias ? Why can not we use this Vbias directly to bias a Current source load ?

    •   AltAdvertisement

        
       

  2. #2
    Junior Member level 1
    Points: 321, Level: 3

    Join Date
    Dec 2017
    Posts
    17
    Helped
    0 / 0
    Points
    321
    Level
    3

    Re: Stable Vbias for Current source load/ Current Mirros

    Well, the whole idea of a stable Vbias voltage is to have a voltage which will not be depended on PVT (Process Voltage Temperature) meaning it will not change with the environment. This is called a BGAP circuit.
    Basically, a simple resistor divider (beside being a really simple circuit) has lots of problems - high Rin, not a very stable voltage, etc...
    We use current mirrors because we want to "copy" a Bias voltage from one transistor to another and we would like to use only 1 voltage (1 battery) instead of having several Bias sources in one circuit (which can increase power consumption for example...)

    hope that's clear.



    •   AltAdvertisement

        
       

  3. #3
    Advanced Member level 5
    Points: 39,304, Level: 48

    Join Date
    Mar 2008
    Location
    USA
    Posts
    6,355
    Helped
    1850 / 1850
    Points
    39,304
    Level
    48

    Re: Stable Vbias for Current source load/ Current Mirros

    1) You don't, unless you care about knowing the value
    2) You can, if you don't care about outside influences
    3) Because you want more than one that's the same value
    4) Because bandgap is the best you can fo, at low voltage,
    Because voltage is not current, and needs to be transformed
    to get the result sought.

    All of these are really, really fundamental questions whose
    answers could probably have been found read in the time
    you were waiting for the grapes o' wisdom to fall into your
    mouth. And you may only get a raisin.



--[[ ]]--