+ Post New Thread
Results 1 to 4 of 4
  1. #1
    Member level 5
    Points: 617, Level: 5

    Join Date
    Nov 2017
    Posts
    82
    Helped
    0 / 0
    Points
    617
    Level
    5

    Output of OTA with capacitor or without capacitor

    Hi

    Can someone tell me if I am simulating OTA circuit do I hav eto placea capacitor or resistor at the output or not?What would be the difference if I do not place any capacitor resistor at the output?

    I tried I observed the change in the phase margin only if I place a capacitor? is there any other parameter difference

    Thanks

    •   AltAdvertisment

        
       

  2. #2
    Full Member level 1
    Points: 763, Level: 6

    Join Date
    Jan 2019
    Location
    Belgium
    Posts
    101
    Helped
    51 / 51
    Points
    763
    Level
    6

    Re: Output of OTA with capacitor or without capacitor

    Quote Originally Posted by ICdesignerbeginner View Post
    Hi

    Can someone tell me if I am simulating OTA circuit do I hav eto placea capacitor or resistor at the output or not?What would be the difference if I do not place any capacitor resistor at the output?

    I tried I observed the change in the phase margin only if I place a capacitor? is there any other parameter difference

    Thanks
    If you place a resistor, then make sure the resistor is much larger than your output impedance else your gain will drop. To drive resistors, you need to follow your OTA stage with a source follower.
    Placing a capacitor will change the location of your pole and it is quiet expected you will see a phase margin variation.



    •   AltAdvertisment

        
       

  3. #3
    Full Member level 1
    Points: 987, Level: 7
    ashrafsazid's Avatar
    Join Date
    Sep 2016
    Location
    Germany
    Posts
    102
    Helped
    1 / 1
    Points
    987
    Level
    7

    Re: Output of OTA with capacitor or without capacitor

    A good practice of designing OTA ( I assume here OTA, high output Z) is to keep the load as a non-dominant pole far from the dominant one which sets the gain and the BW. Following this, you will obviously ensure proper PM for your circuit. Hence, it would be applicable for different capacitive load in 'tolerable' range and you should not see any major impact of this capacitive loads on your OTA. In the case you will be driving some other resistive load, make sure that the OTA has the driving capability for a certain resistive sizing, will demand high current and anyway the non-dominant pole will be far away from the gain or dominant pole.

    Hope this helps.
    Your life is all about ΔΣ, the narrow you estimate it, the precise it is ...



    •   AltAdvertisment

        
       

  4. #4
    Full Member level 1
    Points: 1,100, Level: 7

    Join Date
    Feb 2017
    Location
    Philippines
    Posts
    107
    Helped
    16 / 16
    Points
    1,100
    Level
    7

    Re: Output of OTA with capacitor or without capacitor

    Can someone tell me if I am simulating OTA circuit do I hav eto placea capacitor or resistor at the output or not?
    f you place a resistor, then make sure the resistor is much larger than your output impedance else your gain will drop. To drive resistors, you need to follow your OTA stage with a source follower.
    Placing a capacitor will change the location of your pole and it is quiet expected you will see a phase margin variation.
    Hello,
    Isn't simulating without capacitors and resistors is testing the the OTA in no load conditions? I think this is done as a laboratory experiment to see the behavior of an OTA. Moreover, correct me if I'm wrong, an output capacitance is specified (the OTA is designed to drive a certain max capacitance load e.g. the Cgs of the transistor being driven or the input of the next stage). So the OTA should be designed with the specified output load in mind.



--[[ ]]--