A 1.25-V micropower Gm-C filter based on FGMOS transistors operating in weak inversion

This paper presents a novel linearized transconductor architecture working at 1.25 V in a 0.8-μm CMOS technology with very low power consumption. The special features of the floating-gate MOS (FGMOS) transistor are combined in weak and strong inversion leading to a simplified topology with fewer stacked transistors and a very low noise floor. The design methodology is thoroughly explained, together with the advantages and disadvantages of working with the FGMOS transistor. Furthermore, second-order effects arising from nonideal behavior of the device are analyzed and limits for the performance are established. Experimental results from a second-order low-pass/bandpass filter that was implemented using the transconductor show a tunability of over one and a half decades in the audio range, a dynamic range of over 62 dB, and a maximum power consumption of 2.5 μW. These results demonstrate the suitability of the FGMOS transistor for implementing analog continuous-time filters, while at the same time pushing down the voltage limits of process technologies and simplifying the circuit topologies to obtain significant power savings.