An All-Digital Quadrature RF Transmitter Front-End Using 3-bit ΣΔ Modulators in 65-nm CMOS

An all-digital quadrature RF transmitter front-end using 3-bit ΣΔ modulators and applied to low bandwidth sub-GHz applications such as walkie talkie or NB-IoT et.al, has been implemented in 65-nm CMOS. Comparing with traditional RF transmitter front-end based on single-bit ΣΔ modulators [3], our architecture can achieve about 23dB lower OOB (out-of-band) noise. Moreover, it can keep the linearity close to single-bit ones. So, complex and hardware intensive digital predistortion is no longer an essential. The post-simulation ACPR is 60dB for a 180KHz NB-IoT channel at 900MHz. The total power consumption is 9.4mW at 3.6GHz clock frequency with a supply voltage of 1V, and the total chip area is 0.71mm
²
.