Ultra-low power RFIC design using moderately inverted MOSFETs: an analytical/experimental study

This paper studies the use of moderately inverted MOS transistors in ultra-low power (ULP) RFIC design. We introduce a new figure of merit for a MOS transistor, i.e., the g
_m
f
_T
-to-current ratio, (g
_m
f
_T
/I
_D
) which accounts for both the unity-gain frequency and current consumption during the optimization process of the transistor's performance. Using this figure of merit while taking into account the velocity saturation of short-channel MOS devices, it is shown both experimentally and analytically that the g
_m
f
_T
/I
_D
reaches its maximum value in moderate inversion region. Moreover, we analytically investigate the noise behavior of the MOS transistor during the transition from weak inversion to strong inversion region. The measurement results have been obtained for an NMOS transistor fabricated in Jazz Semiconductor's CMOS process