1-V DTMOS-Based Class-AB Operational Amplifier: Implementation and Experimental Results

In this paper, we describe a novel low-voltage class-AB operational amplifier (opamp) based on dynamic threshold voltage MOS transistors (DTMOS). A DTMOS transistor is a device whose gate is tied to its bulk. DTMOS transistor pseudo-pMOS differential input pairs are used for input common-mode range enhancement, followed by a single ended class-AB output. Two versions of the proposed opamp (opamp-A and opamp-B) were fabricated in a standard 0.18-mum CMOS process technology. Measurements under 5 pF and 10 kOmega load conditions gave, for opamp-A, a DC open-loop gain of 50.1 dB, and a unity gain bandwidth (GBW) of 26.2 MHz. A common-mode rejection ratio (CMRR) of 78 dB, and input and output swings of 0.7 V and 0.9 V, respectively, were achieved. Opamp-B has been optimized for biomedical applications, and is implemented to build the analog front-end part of a near-infrared spectroreflectometry (NIRS) receiver of a multi-wavelength wireless brain oxymeter apparatus. A DC open-loop gain of 53 dB, a GBW of 1.3 MHz, and input and output swings of 0.6 V and 0.8 V, respectively, were measured. Opamp-A consumes 550 muW with an input referred noise of 160 nV/radicHz at 1 kHz. Opamp-B consumes only 40 muW and exhibits a lower input referred noise of 107 nV/radicHz at 1 kHz