ABCs of bias generators

Members: Cornelia Fermuller, Jayawan Wijekoon, Roi Kliper, Rajit Manohar, Ravi Shekhar, Runchun Wang, Samantha Adams, Siddharth Joshi, Timir Datta, Tobi Delbruck, Terry Stewart, Yan Wu

Leaders: Tobi Delbruck

Learn how to make on-chip bias current references using Widlar bootstrapped mirrors and Bult and Geelen current splitters. These circuits will make your chips work better and make your users happier. See  http://jaer.wiki.sourceforge.net/biasgen for more details.

Tutorial Material

• See attachment:bias1.pdf for the annotated tutorial slides

Background

The image below shows the bootstrapped mirror feeding a current splitter. This basic architecture is used for all the bias generators we have built.

The illustration below shows the architecture of the programmable bias generators used on [ our DVS128 dynamic vision sensor silicon retina]. The same current splitter is used together with shift register latches and t-gates to steer and buffer a fraction of the master current for each bias.

Schedule

The plan is for 4 blackboard tutorial sessions

1. Introduction and motivation for on-chip bias generation - demonstrations of existing systems. Widlar's bootstrapped mirror.
2. Widlar's bootstrapped mirror continuation - startup and performance.
3. Bult & Geelen's current splitter and its characterization.
4. Programmable bias generator and it's future development.

Resources

• The central repository is  http://jaer.wiki.sourceforge.net/biasgen. This is kept up to date with the design kits.

Some papers we have published on bias generators are below

•  32-bit Configurable bias current generator with sub-off-current capability, T. Delbruck, P. Lichtsteiner, R. Berner, C. Dualibe, in ISCAS 2010, Paris, pp. 1647–1650. - The latest published programmable bias generator with sub-off-current capability and fully configurable bias buffers.
•  Fully Programmable Bias Current Generator with 24 Bit Resolution Per Bias, (2006) Delbruck, T., Lichtsteiner, P, International Symposium on Circuits and Systems (ISCAS 2006),. 21-24 May 2006 Page(s):2849 - 2852. The first published programmable bias generator
•  Bias generators with wide dynamic range. (2005). T. Delbruck, A. van Schaik, Analog Integrated Circuits and Signal Processing, vol . 43, pp. 247-268. - Journal paper about the fixed-current bias generator with lots of details about the Widlar bootstrapped mirror and the current splitters.

The original current slitting principle is described in the paper below, along with another paper on current splitter accuracy

• An Inherently Linear and Compact MOST-Only Current Division Technique, Klaas Bult and Govert J. G. M. Geelen, IEEE J. Solid State Circuits, 1992, pp. 1730-1735 - Original paper about current splitters.
•  2007 ISCAS paper about accuracy of current splitter

See the attachments for other interesting papers from the group of Bernabe Linares-Barranco and 'teresa serrano-gottaredeno', who invented the sub-off-current (or as they call it, sub-pA) mirror and who have developed interesting ways of using current splitter statistical variation to improve accuracy.