A CMOS radio frequency low noise amplifier with high linearity and low operation voltage of less than 1.0V is presented.In this circuit,an auxiliary MOSFET in the triode region is used to boost the linearity.Simulation shows that this method can boost the input-referred 3rd-order intercept point with much less power dissipation than that of traditional power/linearity tradeoff solution which pays at least 1dB power for 1dB linearity improvement.It is also shown that the size of the common-gate PMOS transistor needs to be optimized to reduce its loaded input impedance so as not to degrade the linearity due to high voltage gain at its source terminal.The simulation is carried out with TSMC 0.18μm RF CMOS technology and SpectreRF.
A design of a linear and fully-balanced operational transconductanee amplifier （OTA） with improved high DC gain and wide bandwidth is presented. Derivative from a single common-source field effect transistor （FET） cas- cade and its DC I-V characteristics,the third-order coefficient g3 hasbeen well compensated with a parallel FET operated in the triode region, which has even-odd symmetries between the boundary of the saturation and triode region. Therefore,for high linearity,a simple solution is obtained to increase input signal amplitude in saturation for the application of OTA continuous-time filters. A negative resistance load （NRL） technique is used for the compensation of parasitic output resistance and an achievement of a high DC-gain of the OTA circuits without extra internal nodes. Additionally, derivations from the ideal -90° phase of the gm-C integrator mainly due to a finite DC gain and parasitic poles will be avoided in the frequency range of interest. HSPICE simulation shows that the total harmonic distortion at 1Vp-p is less than 1% from a single 3.3V supply. As an application of the VHF CMOS OTA,a second-order OTA-C bandpass filter is fabricated using a 0. 18μm CMOS process with two kinds of gate-oxide layers, which has achieved a center frequency of 20MHz,a 3dB-bandwidth of 180kHz,and a quality factor of 110.
