Analysis and Design of a Low-Voltage, Low-Power, High-Precision, Class-AB Current-Mode Subthreshold CMOS Sample and Hold Circuit

This paper proposes the design of a current-mode sample and hold circuit using subthreshold MOSFETs. The proposed circuit combines negative feedback and the compressive I-V characteristic of a class-AB weak inversion transconductor to achieve low switching error, high signal-to-noise ratio and high dynamic range from a low supply voltage and very low current consumption. The paper also provides a feedback analysis of current mode sample and hold circuits. Several design issues including circuit stability, mismatch, linearity, noise, and power consumption are discussed and a comparison of class-A and class-AB versions of subthreshold sample and hold circuits is made. The design verification of the proposed class-AB current mode sample and hold circuit is done by circuit simulations using 0.13 μm CMOS model parameters. The results show that, from a 0.6 V supply and with a power consumption of 27.5 nW, the proposed circuit provides 73 dB signal-to-noise ratio, 77 dB dynamic range, and a figure of merit of 1.9 nW/MHz.