Fully Integrated CMOS Switching Power Mixer Array for Linearization and Back-Off Efficiency Improvement

Non-constant envelope modulation schemes have become commonplace in cellular applications due to their higher spectral efficiency. Linear PAs driven by an RF transmitter are usually used to generate these signals faithfully at the expense of power efficiency. Separate processing of amplitude and phase information (e.g., EER or polar modulation) has been proposed [1] as a way of improving the system power efficiency. However, many of these schemes require an efficient high-power low-frequency supply modulator to reconstruct the amplitude information. This can be done, for instance, using a switching DC-to-DC converter with its own limitations in efficiency, bandwidth, and area that also requires an external inductor [2]. Even for an ideal supply modulator, the amplitude dynamic range of the PA itself is limited by the gate-to-drain feedthrough and its associated AM-to-AM and AM-to-PM conversion. (For example, in [3] a 10dB change in the supply results in a 5° phase shift at the output.) Although a digitally-modulated polar PA [4] has been shown as a possible solution at lower power levels, its implementation in a wideband watt-level fully-integrated CMOS PA for non-constant modulation has not yet been demonstrated.