At sub-THz frequencies, the local oscillation for transceivers is often generated by an analog frequency multiplier tree. This paper studies the origins and minimization of spurious tones in a local oscillator multiplier consisting of a chain of multiply-by-2 frequency doublers. It is found that the nearest spurious components depend on the leakage of the input signal in the first multiplier, and this can be minimized by filtering in the first stage, better balance in the driving differential signal, or by active bias tuning. To verify modeling of the non-linearity, 0.13um SiGe BiCMOS technology has been utilized.