Stabilized Current Source in 180 nm CMOS

This paper presents a comparative analysis of four CMOS stabilized current source architectures: the beta-multiplier, an op-amp-enhanced beta-multiplier, the Nagata current source, and a modified Nagata source with active feedback based on an op-amp. The study focuses on evaluating their performance in terms of thermal stability, dependence on supply voltage and the output noise current spectral density. Analytical considerations were validated through simulation using the Mikron JSC 180 nm 1.8 V CMOS process. The findings reveal the trade-offs between circuit complexity, supply voltage and temperature independence, as well as noise level. The op-amp-enhanced Nagata current source is the best of the considered circuits and has the following characteristics: nominal current 15.14 µA, supply voltage dependence of the reference current 0.1 µA/V, RMS output noise current 63.98 nA (within 0.1 Hz to 1 MHz band), current temperature coefficient 66.15 ppm/°C. This circuit has been chosen for the layout implementation. Layout sizes are 18×28 µm.