Mismatch compensation of CMOS current mirrors using floating-gate transistors

The simple CMOS current mirror is a fundamental compositional element which is employed in a wide variety of analog and digital circuit designs. The use of CMOS current mirrors is appealing to circuit designers given the low cost associated with CMOS fabrication and the inherent simplicity of operation. Unfortunately, the simplicity of the CMOS current mirror makes it particularly susceptible to device mismatch due to process variations. In recent years the use of floating gate transistors for mismatch compensation has become increasingly popular. We report on our observations regarding the efficacy of this technique in both weak and strong inversion and present analytical and simulated results quantifying these observations. The central result is that although compensation using floating gates works well for correcting mismatch for subthreshold operation, similar compensation in above threshold operation results in the introduction of previously unseen mismatch effects.