How to analyze two analog IC blocks( Pls see attached file)?

[D2004]

Hi all,

Is there any guru in analog IC circuit design?
Could you give me any clue on the two analog cmos IC blocks (pls see the attached file: AnalogICcircuit.pdf), especially the second one?

Thanks.

David.

 

[Fom]

Re: How to analyze two analog IC blocks( Pls see attached fi

I think it is some kind of current reference. It is independent on VDD change and process deviation. Can you give transistor sizes or ratio?

 

[D2004]

Re: How to analyze two analog IC blocks( Pls see attached fi

Thanks, Fom.
However, no sizes or ratio given.

 

[roshdyh]

Re: How to analyze two analog IC blocks( Pls see attached fi

Hi D2004 I agree with FOM.
I guess also the resistance controls the current value in the second block

Hi all,

Is there any guru in analog IC circuit design?
Could you give me any clue on the two analog cmos IC blocks (pls see the attached file: AnalogICcircuit.pdf), especially the second one?

Thanks.

David.

 

[electronrancher]

first one i talked about in the other post, second one is a diff pair for current - a crude LCA (linear current amp).

you can back-solve using the gds/ids equations, but here's a quick example.

set IIN1 to a reference current (say 1uA - keep it small because it acts as a diff pair so for one sided operation OUT2 won't turn on until IN2 >1uA)

set R2/R1 to a ratio - try 2:1 for fun. I think the formula is Iout = Iin(1+(R2/R1)

now sweep IIN2 from 0-100uA. IOUT2 gives 0-300uA.

example 2:
set R2/R1 to 50k:10k and sweep IIN2 0-100uA.. IOUT2 gives 0-600uA

this circuit is HIGHLY dependent on process (it has a serious dependence on VGS & W/L), so it's not really any good for integrating.

 

[D2004]

Re: How to analyze two analog IC blocks( Pls see attached fi

Hi electronrancher,

Intuitively, I think your analysis is right. However, I could not derive your
formula Iout = Iin(1+(R2/R1). In my equation, the Iout/Iin ratio always depends on gm.

Could you give a further explanation on how to derive the formula?

I will go to lab to sweep your examples later? Thanks.

 

[electronrancher]

Hmm. Assuming rout and Vgate is the same for both devices a diode connected device would have Vgs=Vt + Vdsat. For this resistor network we can say deltaVgs is set by the ratio of resistors to the ratio of currents, so to give equivalent Vgate the current would follow the 1+R2/R1. I have some sims somewhere that show that, at first glance I was going to guess just R2/R1 but saw my mistake in sim.

I can dig them up if you want.

 

[D2004]

Re: How to analyze two analog IC blocks( Pls see attached fi

Sorry. I still could not follow. I am looking forward to your further analysis. Thanks.

 

[uncle_urfi]

Re: How to analyze two analog IC blocks( Pls see attached fi

May be this paper will help. I think this is a self-biased current source. It would have been nice to have some input and output labelled along with transistor sizes.


1 A low-power differential CMOS bandgap reference
Brooks, T.L.; Westwick, A.L.;
Solid-State Circuits Conference, 1994. Digest of Technical Papers. 41st ISSCC., 1994 IEEE International , 16-18 Feb. 1994
Pages:248 - 249