wide swing cascode current mirror using pmos

[020170]

pmos wide swing current mirror

typical wide swing cascode is shown below. (Fig A)


some wide swing cascode circuit uses pmos instead of nmos.
example is shown below. (Fig B)


Pmos is used as diode connected nmos. however I don't know how it works exactly. Is it Possible to use pmos is not connected drain & gate terminal ?

How can you say pmos is diode-connected mos?

in additional, I want to know what is disadvantage & advantage about Fig B circuit.

thanks

 

[DenisMark]

wide swing cascode current mirror

PMOS on pic. B works as commod-drain stage (aka source follower). It provides level shift to proper biasing of cascode NMOSs, the circuit should meet to condition VgsNcascode-VgsP > VovNmirror. From this condiditon the main drawback of pic.B is raised. It is less robust to PVT and input current variation than pic.A. It requeres some margin VgsNcascode-VgsP over VovNmirror so it provides less swing.