Digital pulse-width pulse-position modulator in 28 nm CMOS for carrier frequencies up to 1 GHz

A fully digital pulse-width pulse-position modulator (D-PWPM) is proposed that is capable of providing pulse sequences for a switching-mode power amplifier. The pulse sequences are generated according to 6-bit digital input words defining the positions of the rising and falling edges without the need for tunable analog delay cells. All possible edge positions are derived by division and phase interpolation of a digital input clock signal that is a multiple of the carrier frequency. CMOS selectors provide two signals which carry the actual rising and falling edge positions to special symmetric CMOS NOR and NAND gates. They finally generate the modulated pulse sequence. The D-PWPM is fabricated in a 28 nm low-power CMOS technology and the circuit core dissipates 53mW from a 1 V supply. Sinusoidal double-sideband suppressed-carrier modulation of a 1 GHz carrier demonstrates the capability of the D-PWPM to operate as an RF bandpass mode DAC. With a carrier frequency of 983.04MHz, an SFDR of 45.6 dB is achieved for a low-frequency modulation and 33.4 dB near Nyquist frequency. Data transmission at 491.52MBit/s is demonstrated with a 16-QAM.