1.  Field of the Invention
The present invention is generally in the field of semiconductor circuits.  More particularly, the present invention relates to semiconductor circuits for low power applications. 
2.  Background Art
A conventional flip flop is a memory storage device that typically retains stored data as long as it is powered on (or “turned on”).  While not in active use, but while still turned on and retaining stored data, the flip flop wastes power because transistors in the flip flop have leakage current.  While turned off, the transistors have no leakage current, and thus the flip flop does not waste power, but the flip flop also loses stored data. 
In an application using conventional flip flops in which power consumption is a design factor, such as in a low power mobile application, the amount of power wasted due to leakage current of inactive flip flops can be reduced in conventional ways.  For example, the flip flops can be turned off while inactive, resulting in a power saving at the cost of losing stored data.  Turning the flip flops back on for active use may involve reading data back into the flip flops from a nonvolatile source, resulting in increased circuit complexity and lost time.  Alternatively, the flip flops can be implemented as conventional balloon flip flops, which in active use retain data in master and slave circuits, and while turned on but inactive (i.e., in a “sleep mode”) retain data in conventional balloon circuits.  In this alternative, fabrication of the balloon circuits requires a large number of additional components, and transferring data to and from the balloon circuits can require complex timing signals and circuitry.  In both alternatives, the use of conventional flip flops results in various disadvantages such as, for example, increased complexity, increased cost, and/or reduced performance. 
Thus, there is a need in the art for a data retention flip flop that overcomes disadvantages of conventional flip flops.