Linearity-enhanced Low-Power Distributed Low-Noise Amplifier in CMOS

Distributed amplifiers enable achieving very high gain-bandwidth products. This is achieved by means of combining the output current of transistors placed along tapped delay lines. Due to the need for half of the output current to be dissipated in a termination resistor, and the additive instead of multiplicative gain-contribution of the stages., the distributed amplifier is easily dismissed as being too inefficient for low-power applications. However, applying transmission line tapering and other techniques, the distributed amplifier is able to match the low power-consumption (13 mW) of resistive-feedback amplifiers while offering a high gain (15.8 dB) over a 22 GHz bandwidth [1] (Fig. 1-2). In addition, the amplifier features an average noise figure of only 5.4 dB across the 22 GHz band. Due to optimization for mimimum power-consumption and the high gain, the presented amplifier does exhibit relatively low linearity (average IIP3 of -7.3 dBm). However, the cascaded topology allows tuning the first stage for noise and the second stage for linearity, facilitating the design of a highly-linear low-noise amplifier. Driving the second-stage transistors more into saturation, linearity performance can be increased dramatically (0 dBm IIP3), but at the cost of increasing the power consumption to 47 mW. The gain also increases to 18 dB. In order to limit the increase in power consumption, degeneration resistors can be employed [2]. Inserting 30-Ohm resistors (Fig. 3) lowers the gain to 14 dB and the power consumption to 26 mW, but retains the high linearity (0 dBm IIP3). The resulting amplifier topology offers all the properties of the original design, but additionally shows much improved linearity performance at only a moderate increase in power consumption. [1] B. Machiels, P. Reynaert, and M. Steyaert, “Power efficient distributed low-noise amplifier in 90 nm CMOS”, in Radio Frequency Integrated Circuits Symposium (RFIC), 2010 IEEE, May 2010, pp. 131 –134. [2] R. Baki, T. Tsang, and M. El-Gamal, “Distortion in RF CMOS short-channel low-noise amplifiers”, Microwave Theory and Techniques, IEEE Transactions on, vol. 54, no. 1, pp. 46–56, Jan. 2006.status: publishe