Understanding Voltage Rails in High-End Processors

F

FreshmanNewbie

Advanced Member level 1
Advanced Member level 1
Joined
May 10, 2020
Messages
464
Helped
0
Reputation
0
Reaction score
3
Trophy points
18
Activity points
4,594
I have observed that high-end processors typically operate at relatively low voltage levels, often around 1.2V or even lower. I am curious to understand how such low voltage levels are sufficient for the operation of these devices.

Through my research on this forum, I have learned that CPUs generally have multiple power rails, such as those for the core and I/O, each operating at different voltages.

I would like to gain a deeper understanding of the reasoning behind using separate voltage rails for the core and I/O. Additionally, I am interested in knowing which of these rails typically requires higher current and the underlying reason for this higher current demand. Any insights would be really helpful.
 

Sort by date Sort by votes
I assume you understand the ratio of Vgs/Vt for Vds with lower Q=CV and reduction of Vt with wavelength of lithographic wafers.

For the fastest CPUs with super low voltage capability, a Vt of 0.2V–0.3V is a reasonable estimate based on current trends.

My Rule of Thumb (RoT) is Vgs/Vt = 2 is nominal Ron and reducing this ratio increases Rds*Cout = Tau while reducing clock rates as Ron = Vdd/Id increases with Vgs=Vds. While increasing Vdd reduces on and transition time while clocks selected to faster rates it also increases the current during transition which is a linear shoot-thru by design to maintain impedance it does limit the ratio of Vdd Max/Min in all CMOS as this dynamic power to some exponent< ^4?) that I forget. The original CD4xxx high voltage types which had a Vt= 1.5V and Beta ~= 0.05 had a very high ratio of Vdd max/min.

While traditional Power FETs with Vgs(th) = 2 to 4 V, my RoT is to use 2.5 x Vgs(th) for RdsOn. and lower for the "subthreshold types."
 

Upvote 0 Downvote
You must log in or register to reply here.

Similar threads