A new predistortion linearizer using low frequency even order IM components

We present a new predistortion linearizer using low frequency even-order components. An I/Q balanced modulator is adopted as a generator of the 3rd and 5th order IM (intermodulation) components. It is very compact and could independently control the amplitudes and phases of the IM components. We have analyzed the delay mismatch effect of these predistortion circuits. The result shows that the 5th order IM components are twice as sensitive as the 3rd ones. The predistorter is implemented and tested at the IMT-2000 band. Two tone test results show that the IM3 cancellation is about 23-25 dB and the IM5 is cancelled by about 12-20 dB. The ACPR is improved by more than 11 dB for the broadband CDMA signal with a chip rate of 4.096 Mcps and this improvement is maintained through a broad range of output power level.