A CMOS IQ direct digital RF modulator with embedded RF FIR-based quantization noise filter

This paper presents a new approach to reduce the out of band quantization noise of Direct Digital RF Modulators (DDRM). The DDRM is organized in a FIR-like configuration to filter the quantization noise in the RX band directly at RF. To demonstrate the principle, a 0.9 GHz FIR IQ DDRM has been integrated in 130 nm CMOS. The transmitter achieves more than 22 dB reduction in the quantization noise floor to reach -152 dBc/Hz@20 MHz with a 200 kHz baseband tone. The actual DDRM is capable of both amplitude and phase modulation by using a new four-phases IQ architecture. This results in a reduced power consumption and chip area. The transmitter consumes 94 mW from a 2.7 V supply and achieves an average output power of 9.5 dBm. Leakage into the adjacent channel and into the next one of -35 dB and -53 dB, respectively have been measured for a 10 MHz OFDM signal. It also achieves -27.2 dB EVM with a 64QAM input signal.