236 {\mu}W Direct-RF PLL-Free Multi-PSK Transmitter Using Oscillator-Based Phase Synthesis

TL;DR

This paper introduces a compact, low-power direct RF multi-PSK transmitter that eliminates the need for a PLL by performing phase modulation directly within a ring oscillator, suitable for low-power wireless applications.

Contribution

It proposes a PLL-free, oscillator-based phase synthesis method with reconfigurable multi-mode modulation supporting various PSK schemes in a unified hardware structure.

Findings

Operates at 2.4 GHz with 2 MSps symbol rate

Consumes only 236 μW excluding output driver

Achieves 5.13% EVM at 2 MSps

Abstract

This paper presents a compact, low-power, direct RF multi-phase-shift keying (PSK) transmitter (TX) that eliminates the need for a phase-locked loop (PLL) by performing phase modulation directly within a ring oscillator. The proposed architecture exploits synchronized charge extraction at the oscillator's transition points to induce controlled phase shifts while maintaining constant amplitude and frequency. A time-domain multi-triggering technique is introduced to enable reconfigurable multi-mode modulation, supporting 16-PSK, 8-PSK, QPSK, and BPSK within a unified hardware structure. The TX circuit is fabricated in a 22-nm FD-SOI process and operates in the ISM band at 2.4 GHz. Measurement results indicate a symbol rate of 2 MSps with a maximum error vector magnitude (EVM) of 5.13% rms. The core TX occupies 23 {\times} 17.6 {\mu}m2 and consumes 236 {\mu}W, excluding the output driver, which delivers -10 dBm output power over a 60 MHz bandwidth. The proposed design achieves a favorable trade-off between power consumption, circuit complexity, and modulation flexibility, making it well-suited for low-power wireless applications.