Linearization Technique Suppresses Third-Order Intermodulation

To satisfy the needs of low-cost wireless terminals, many single-chip RF receivers have been developed with CMOS technology. In the presence of strong interferers, however, the third-order nonlinearity of an RF receiver front end generates third-order intermodulation signals that can overlap with the desired signals. A new linearity technique generates and injects low-frequency, second-order intermodulation to suppress such third-order modulation. This technique was proposed by Shuzuo Lou from Hong Kong Applied Science and Technology Institute and Howard C. Luong from the Hong Kong University of Science and Technology.

The researchers applied their proposed technique to a low-noise amplifier (LNA) and downconversion mixer in an RF front end operating at 900 MHz. Working off a +1.5-VDC supply with a total current of 13.1 mA, the RF receiver front end delivers 22 dB gain with a 5.3-dB noise figure. The linearization technique achieves roughly 20 dB third-order intermodulation suppression. It improves the receiver front end's input-referred third-order intercept point from 10.4 dBm to +0.2 dBm while requiring just 0.1 mA additional current. See "A Linearization Technique for RF Receiver Front-End Using Second-Order-Intermodulation Injection," IEEE Journal Of Solid-State Circuits, November 2008, p. 2404.