Merging of RF Oscillator and Power Amplifier to Enable Fully Integrated Transmitters for Internet-of-Things

To facilitate the ever-increasing influx of the Internet-of-Things (IoT) wireless connectivity, the investigation for power efficient and cost effective wireless devices together with the trend towards fully integrated solutions have opened up a new wave of challenges and opportunities for ultra-low-power (ULP) RF integrated circuit design. The full integration of the power- hungry battery-operated CMOS transmitter (TX) is especially challenging and confronted by the down-scaled power supply, lossy on-chip passives and low-resistivity silicon substrate of nanoscale CMOS technology. This sets different requirements for devices working in different RF bands, mainly the 900 MHz (sub-GHz) and 2.4 GHz bands in terms of range coverage, data rate, maximum allowed RF power, etc. Specifically, the Bluetooth Low Energy (BLE) as the mainstream standard for IoT applications in that the 2.4 GHz band is constrained by the transmitter system efficiency ?TX due to the fact the power dissipated by the modulator PDC,MOD is generally comparable or even higher compared to the delivered RF power PRF by the power amplifier (PA). Furthermore, PDC,MOD cannot scale down when the PA operates at large power back-off. On the other hand, the 802.11ah, or equivalently WiFi-HaLow, sits in the 900 MHz (sub-GHz) band targeted for long-range wireless connectivity which faces the greatest challenge of inexpensively integrating the RF passive components, especially inductors and transformers utilized for frequency generation or impedance matching. In this thesis, we propose to merge the oscillator (the most power-hungry block in the modulator) and the power amplifier either in the way of “functionally merged” DCO-PA for BLE transmitters in order to boost the system efficiency at large power back-off or in the way of “physically merged” DCO-DPA for WiFi-HaLow transmitters to tremendously reduce the die area. One chip prototype is fabricated to demonstrate the sub-GHz 802.11ah transmitter (TX) with a physically merged digitally controlled oscillator (DCO) and digital power amplifier (DPA) saving ~50% of area. The resulting DCO pulling by the DPA is compensated via a feedback path and an inter-winding cancellation capacitor suppresses the 2nd harmonic. Further, we introduce a super-simple RF front-end with a fully integrated matching network for 2.4 GHz TDD radios featuring a functionally-merged single-MOS DCO-PA and a zero-shifting capacitor that suppresses the 2nd harmonic emission. This not only allows to share the same antenna pin with the RX but also provides passive-gain boosting to an RX low noise amplifier (LNA).