+14 dB improvement in the IIP3 of a CMOS active mixer through distortion cancellation

The derivative superposition (DS) technique is used to cancel the third-order intermodulation distortion (IMD) produced in a downconverter mixer. By providing separate bias currents to the mixer core and the distortion-cancelling circuitry, the IMD is reduced but the conversion gain remains nearly the same in the distortion-cancelling mixer compared to the baseline mixer without linearization. Measurements show that the distortion-cancelling mixer has an IIP₃ that is 14 dB above the IIP₃ of the baseline mixer while the conversion gain drops by only -0.7 dB. The distortion-cancelling mixer only needs an additional 2.4 mW of dc power relative to the baseline mixer's power draw. The test chip was fabricated in a standard 130 nm CMOS process and occupies an active area of 0.1 mm².