Design techniques for CMOS broadband circuits towards 5G wireless communication

The framework of 5G communication is currently being developed worldwide. To enable 5G, one of the key challenges worldwide is bandwidth shortage. mmWave technology offers very wide bandwidth with low spectrum congestion. At the same time, advanced CMOS process is fast enough to operate in the mmWave frequency range. Due to its cost and integration advantage CMOS makes fully integrated mmWave transceivers, possible.

This thesis has addressed multiple sub-blocks which can enable 5G, such as broadband circuits for mmWave quadrature generation in the form of a two-stage polyphase filter, power amplifier (PA) and transmitter. Power efficiency is an important criteria for portable radios and is mainly determined by the PA. Non-linear PAs cannot be used in conventional transmitter architectures. Thus there is an efficiency-linearity trade-off in conventional implementations. This thesis has attempted to weaken this linearity-efficiency trade-off at two levels.
One, by circuit method as in the broadband distortion cancellation technique applied to a mmWave PA. It achieves 22.4dB gain, peak PAE of 23% and saturated output power of 16.4dBm with 8% PAE at 6dB back-off. With <0.8° AM-PM distortion the linearity is demonstrated by amplifying a 3Gb/s 64-QAM signal with 7dBm of average output power and achieve an EVM of -25.2 dB and >35 dB of ACPR.
Two, by an architecture method as in the mmWave outphasing transmitter which is a promising efficiency-enhancement technique. The proposed transmitter is the first application of outphasing technique at mmWave, featuring 15 % average transmitter efficiency when transmitting 500Mb/s 16-QAM with 12.5dBm average output power at an EVM of -22dB.

The 5G networks will also heavily rely on the low-GHz frequencies to provide for mobility and connectivity. This range of spectrum also needs to support variety of legacy standards. Therefore the 5G transmitters should also have lot of flexibility built in. In order to come up with a scalable solution, this thesis has investigated the design of a broadband fully digital 0.9GHz-2.6GHz multimode transmitters based on the concept of RF-PWM. It achieves an EVM of better than -29dB for a 802.11g 64-QAM OFDM signal. It has also been tested with 40MHz single carrier 64-QAM signals. The measured ACPR is below -30dB up to 2GHz and possible improvements are demonstrated.