Broadband LNA Design Employing Noise and Distortion Cancellation (COGUR)
Ali Niknejad and Wei-Hung Chen
One of the key challenges in designing multi-standard multi-mode front-end circuits is the high dynamic range requirement over a wide frequency range. Even in a "digital" receiver application, employing discrete-time signal processing, a linear front-end amplifier is required to reject the noise and relax the performance of the subsequent samplers. The straightforward solution for multi-standard multi-mode front-ends employs reactive tuning and multiple receiving paths at the cost of die and board area, high pin count, and lack of reconfigurability. Recent demonstration of ultra-wideband (UWB) LNAs ranging from several hundreds of MHz up to 10 GHz suggests an alternative that uses a single circuit for contiguous broadband signal receiving and has achieved comparable performances to its narrow-band counterparts by exploiting high fT /fmax transistors available from nano-scale CMOS.
In this project, broadband techniques of noise and distortion cancellation are investigated and incorporated with the common-gate input stage to deliver the simultaneous low noise figure and high IIP3 over a wide frequency range. The role of third-order distortion due to the second-order interaction of the linear and second-order nonlinear outputs is identified and also accounted for in the distortion cancellation design. The scheme is verified by a 0.8~2.1 GHz CMOS LNA in 0.13 µm technology with a measured peak IIP3 of +16 dBm and a noise figure below 2.6 dB. A modified distortion cancellation is applied to a second LNA design aiming to eliminate the IIP3 2-tone frequency dependency observed in the first circuit. The new LNA is carried out in 65 nm CMOS and achieves comparable dynamic range with an extended bandwidth up to 5 GHz in the simulation.
Figure 1: Chip microphotograph of the 0.8~2.1 GHz LNA
- W.-H. Chen et al., "A Broadband Highly Linear CMOS LNA Employing Noise and Distortion Cancellation," Proc. IEEE RFIC Symposium, Honolulu, HI, June 2007, pp. 61-64.