Current Mirror Precision in CMOS: Beyond Threshold Voltage Mismatch

Transistor mismatch critically limits CMOS precision analog circuits, with threshold voltage and transconductance factor (also known as current factor nowadays) variations as the dominant sources. Traditionally, the threshold voltage has been regarded as the primary contributor, while the current factor was considered secondary. This paper analyzes current mirrors implemented with 1.5 V and 5 V devices in a 130 nm CMOS process, combining theoretical modeling with schematic-level simulations. Monte Carlo simulations across −40 °C to 175 °C demonstrate that 1.5 V transistors, though exhibiting reduced threshold variability, display stronger current factor sensitivity due to shorter channels and thinner oxides, leading to larger current deviations. Conversely, 5 V devices show higher threshold dispersion but improved stability from weaker second-order effects. These findings confirm that the current factor cannot be treated as a second-order effect in modern CMOS processes and must be considered in precision analog design.