Internal logic of IO pads

[fragnen]

Do IO Pads have any digital logiv inside them? What is the purpose of that digital logic inside them?

 

[dick_freebird]

The output high and low side switches want their
gates driven to make H, L and Z. You need a trivial
couple of gates for that decode and of course the
drive taper chain (inverters).

 

[fragnen]

The output high and low side switches want their
gates driven to make H, L and Z. You need a trivial
couple of gates for that decode and of course the
drive taper chain (inverters).

Do you want to mean the three state buffer which has three states H, L and Z by

output high and low side switches

in your above statement?

What do you mean by drive taper chain? What is the purpose of this drive taper chain?

 

[D.A.(Tony)Stewart]

Pads are driven by buffers and all cascaded CMOS buffers have a certain taper of lower impedance higher load capacitance for each stage or in other words a higher current conductance which can be derived from Beta = β = 2*Ids / (Vgs - Vt)² for all enhancement FETs.

This increase in conductance * risetime is called a tapered buffer. Now a reverse body bias (RBB) design on input stages allows much lower RdsOn without the major penalty of rising Cin & Cout or Ciss, Coss with minimal penalty in speed.

Bonus question.

How many stages do you think it takes to go from 50 Gohms ||5 pF to 50 Ohm logic for 100 MHz pulses or 500 microohms power half-bridge for 1MHz pulses? i.e. How do you determine the optimal gain in gm for the taper with minimal losses? ( while avoiding shoot-thru with a wide tolerance on Vt.

--- Updated May 9, 2024 ---

FWIW https://www.researchgate.net/public...ody_Biasing_Technique_for_CMOS_Tapered_Buffer