subthreshold analog circuit design
Hi,
For Sub-threshold operation you need to go early 1980, since that was the time where low power was very much interesting. After which technology shifted towards wireless and communication, thus moving towards high speed.
Back to the point, Check for Eric Vittoz, Prof in EPFL., Marc Degrawe, Prof at Univ of Neuchatel, Swiss, Christain Piguet, Prof at Unive of Neuchatel (CSEM, mainly for digital low power circuits).
Papers by these authors in 1980s give basic idea on how to work in weak inversion (Sub-threshold operation).
Hope this helps.
Prakash.