Author Topic: constant-gm bias circuit  (Read 2267 times)

0 Members and 1 Guest are viewing this topic.

Offline promachTopic starter

  • Frequent Contributor
  • **
  • Posts: 878
  • Country: us
 

Offline David Hess

  • Super Contributor
  • ***
  • Posts: 17427
  • Country: us
  • DavidH
Re: constant-gm bias circuit
« Reply #1 on: April 25, 2019, 10:38:28 pm »
They don't they implement constant Gm the same way it is done in bipolar circuits by adjusting the bias current levels?  Or is that what they are proposing?  It was not clear to me.
 

Offline silverback

  • Contributor
  • Posts: 27
  • Country: gb
Re: constant-gm bias circuit
« Reply #2 on: April 26, 2019, 12:17:46 pm »
To obtain constant GM the bias current Id or Ic for transistors should be proportional to absolute temperature, Iptat.
 

Offline David Hess

  • Super Contributor
  • ***
  • Posts: 17427
  • Country: us
  • DavidH
Re: constant-gm bias circuit
« Reply #3 on: April 26, 2019, 01:53:54 pm »
To obtain constant GM the bias current Id or Ic for transistors should be proportional to absolute temperature, Iptat.

Exactly, and doing exactly that was an early innovation in bipolar circuit design.

Why isn't the same thing done in their example?  Is there something about CMOS which makes it untenable?

Thinking about it now, I never noticed such a thing in published CMOS operational amplifier designs but I assumed like later published bipolar designs, they just left that part out.
 

Offline promachTopic starter

  • Frequent Contributor
  • **
  • Posts: 878
  • Country: us
Re: constant-gm bias circuit
« Reply #4 on: May 05, 2019, 08:07:49 am »
Do you guys know how to come up with the equation for RDS4C  ?
 
« Last Edit: May 05, 2019, 09:59:53 am by promach »
 

Offline promachTopic starter

  • Frequent Contributor
  • **
  • Posts: 878
  • Country: us
Re: constant-gm bias circuit
« Reply #5 on: May 07, 2019, 12:35:40 am »
Someone else had derived the answer

 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf