A wideband linearisation technique for non-linear oscillators using a multi-stage polyphase filter

This paper presents a wideband technique to suppress the 3^rd, 7^th, 11^th... order harmonic signal components of non-linear quadrature oscillator signals. To accomplish this, a polyphase filter is used. The fundamental signal passes through, while the (4.i-1)th harmonics are filtered out. Based on complex signal theory, this filtering operation is mathematically derived. The theory has been proven by CMOS implementation of a digital oscillator, a polyphase filter and direct up-conversion mixers, resulting in a broadband transmitter. The measurements clearly show the suppression by the complex filter. For the suppression of the fifth order harmonic, an optimisation method using waveform construction is suggested.