UC San Diego

Many phase modulation schemes generally rely on phase-to-RF and amplitude-to-RF modulation alignment. Splitting a signal into amplitude and phase components and feeding them into separate paths potentially has major advantages. While theoretically achievable, amplitude and phase modulation time alignment remains a challenge.

One of the phase modulation schemes is outphasing. Outphasing, also known as linear amplification with nonlinear components (LINC), improves the efficiency while maintaining linearity. To do so, any arbitrary signal splits into amplitude and phase. Then outphasing modulator generates two constant envelope phase modulated vectors also known as outphasing signals. Since outphasing signals are constant envelope, they can be fed into high-efficiency switching mode power amplifiers (PAs). Therefore, efficiency improves without degrading the linearity. Recombining the amplified outphasing signals after PAs, restores the phase and amplitude of the desired output signal. In this scheme, splitting the input signal into amplitude and phase is handled in digital domain thus reducing the risk of time mismatch between amplitude-to-RF and phase-to-RF modulation. However, outphasing modulator requires four digital-to-analog converters (DACs).

In this thesis an alternative approach is proposed that requires only two DACs, similar to envelope tracking, however it does not suffer from time mismatch. Also, a digital phase modulator based on coupled oscillator outphasing modulator is designed. In this design, varactor inside the oscillators is replaced with an 8-bit cap bank, therefore there is no need for any additional DACs.

A 10-GHz modulator is designed in 45-nm CMOS SOI and output vectors demonstrate close to 360 degrees of phase coverage.