The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> Fully differential amplifier
https://designers-guide.org/forum/YaBB.pl?num=1516201201

Message started by Abhishek D on Jan 17^th, 2018, 7:00am

Title: Fully differential amplifier
Post by Abhishek D on Jan 17^th, 2018, 7:00am

I'm a final year B.Tech student. I'm need for the design of a two stage fully differential amplifier. Can somebody help in the design steps?
I've also attached the schematic for reference.
Thanks in advance :)

Title: Re: Fully differential amplifier
Post by Tako on Jan 23^rd, 2018, 5:24am

Hi!

Sorry for late reply.

If you have the schematic, please tell what the problem is? Why you do not simulate?

Title: Re: Fully differential amplifier
Post by sheldon on Jan 23^rd, 2018, 1:35pm

You don't have a common mode feedback loop

Title: Re: Fully differential amplifier
Post by Clark on Jan 30^th, 2018, 9:42am

Hi Abhishek,

I am assuming you have picked up this two stage diff amp schematic from some Analog Design book, and now you need help on how to size each and every transistor ? Possibly, you would also like to know which simulations to perform and how to perform them.

Before proceeding with design steps and understanding how to size each and every transistor you need to know specifications for your two stage diff amp. To name a few, differential gain, common mode gain, output swing, unity gain bandwidth, PSRR, slew rate , current consumption/power requirement. Having these specifications help you in sizing each transistor. Also, I strongly recommend, you have a clear understanding of which transistor influences which specification of your diff amp.

For instance, you differential gain is dependent on gm of your input differential pair etc.

If you have your specifications then mention them, or we can assume some arbitrary (yet realistic) specification for your diff amp and then proceed.

Also, I don't know for which type of simulation you have setup your testbench but I can see that you have AC component at only negative input. You need to have that at both the inputs for an AC simulation to measure gain (what most people look for when designing an amplifier).

-Clark.