Transmission gate in switching binary in current steering DAC

[PhdSA]

Dear Sir,
I'm working under reimann pump in cmos technology and i found your paper is very interesting.
I'm designin a 3 bit binary differential current steering DAC using transmission gate as a switch in the top and the bottom of my circuit. Thus my problem that when the binary switch from '001' to '110', the rised slope and decreased slope are not identical, as can be seen in figure below

It is necessary that the descent slope and the rise slope should be equal. This provide an asymmetry of the curve and i can’t reconstrut my input signal which is a sinusoidal signal. Moreover, each transition where all the bits change, the rised slope and the decreased slope i are not equal.

So, how can I adjust this asymmetry and maintain the same slope in the rise and decrease direction when all the 3 binary bits are changed from the the first transition to the second.

I’m so grateful if you can help me ;



Best Regards

 

[dick_freebird]

Current steering DACs settle much better with source steering than bang-bang high gate swing.

Looks like the current linearity is your issue? And maybe that is bothered by headroom as you approach the rails, sat to lin transition can't be helped much other than to make the swing range << rail span. Like go between 1/4 and 3/4 span, and then 2X buffer or something with enough open loop gain to drive close to rail if that matters?

But also looks like maybe your switching is RC more than I/C and maybe your current source is poor-linearity or dominated by switch nonlinearity / on resistance.