This paper presents a polar phase-tracking RX (PT-RX) that supports multiple modulation schemes including differential phase shift keying (DPSK), amplitude shift keying (ASK) and amplitude phase shift keying (APSK). By employing a two-point injection method in a wideband digital phase-locked loop (DPLL), the proposed polar PT-RX performs various demodulations without requiring quadrature signal generation or a multi-bit analog-to-digital converter (ADC). Compared with existing PT-RXs, the proposed architecture not only overcomes the trade-off between frequency pulling and image rejection but also provides the equivalent constant gain of a digitally-controlled oscillator (DCO) for robust demodulation. A prototype 5.8mW 2.4GHz polar PT-RX is implemented in 65nm and performs 2.5Mb/s 32-APSK demodulation with ?64dBm sensitivity.