  This paper presents an intracellular feedback control strategy, to regulate
the gene expression process dynamics. For this purpose, two types of genetic
circuits are designed in order to compare concentrations of the input
transcription factor (the desired input) and the protein produced by the
expression of target gene (process output). Genetic Relay Switch and Shifted
Subtractor are proposed and employed to design Discrete Comparator. Also,
another type of genetic comparator is presented named Bistable Comparator.
These synthetic comparators are used to produce the required amount of the
protein that activates the expression of the target gene. Numerical simulation
results, demonstrate the effectiveness of the designed controllers.
