Improved Performance Tradeoffs in Harmonic Injection-Locked ULP TX for Sub-GHz Radios

This article presents a digital-intensive transmitter (TX) architecture for ultralow-power (ULP) wireless communication telemetry applications. A Type-I correction loop is proposed to adjust the frequency of the voltage-controlled oscillator (VCO) and enable the use of harmonically injection-locked (IL) technique without significant spurious tones. Two TXs implementations with different loop filters in the Type-I phase-locked loop (PLL) are demonstrated to suppress the voltage ripple at the VCO input. The proposed implementation not only minimizes the spurs from the correction loop but also overcomes the performance tradeoff between spur suppression, phase margin, and maximum achievable bandwidth. Prototyped in the standard 180-nm CMOS process, the two proposed TXs achieve an energy efficiency of 66.97 and 12.5 pJ/bit, respectively, and occupy an active silicon area of 0.0413 and 0.0435 mm2, respectively, while delivering the same output power of −14 dBm with >60-dB in-band spur suppression.