A built-in calibration system to optimize third-order intermodulation performance of RF amplifiers

A digital built-in calibration (BIC) system is presented to automatically adjust the linearity performance of a tunable RF low-noise amplifier (LNA) operating at 2.4GHz. An envelope detection circuit is used to extract the linearity characteristics at low frequencies, enabling the sampling and digital signal processing at low rates. The output of the envelope detector is digitized before the spectrum calculation with an integrated fast Fourier transform (FFT) for estimation of the third-order intermodulation (IM3) distortion specification of the LNA. The digitally-assisted closed-loop calibration scheme is demonstrated with simulations using a two-tone test with 1MHz tone spacing, a 512-point FFT engine, a 10-bit analog-to-digital converter model, and digital blocks operating with a 51.2MHz clock frequency. The total calibration time is 485μs. The digital blocks were implemented using a standard 0.13μm CMOS technology.