High-Throughput Low-Power Area-Efficient Outphasing Modulator Based on Unrolled and Pipelined Radix-2 CORDIC
Diwei Li, Dixian Zhao · IEEE Transactions on Very Large Scale Integration (VLSI) Systems · 2019
In this article, a high-throughput, high-accuracy, area-efficient, and energy-efficient digital outphasing modulator (OPM) is proposed for millimeter-wave transmitters. This digital OPM is entirely based on the fixed-point unrolled and pipelined radix-2 COordinate Rotation Digital Computer (CORDIC) algorithm, which is suitable for outphasing transmitters based on both IQ and phase modulation architectures. The outphasing angle is calculated by a mixture of single-CORDIC and double-CORDIC algorithm, which significantly reduces the critical path delay. Due to architectural advantages, its error performance, sampling rate, power efficiency, and area efficiency are improved. According to FPGA implementation measurements, this architecture enables a 12-bit OPM to achieve error vector magnitude (EVM) of 0.062% and peak sampling rate of 0.74 GSample/s. According to the postlayout spice-level simulation in 65-nm CMOS, a high-throughput version can work at a peak data rate of 1.85 GSample/s at 1-V supply. A low-power version reduces the area consumption to only 0.088 mm2, consuming 28.1 pJ/Sample at 0.78 GSample/s at 0.8-V supply. The proposed high-throughput OPM with the minimized area is expected to further open up an application area of energy-efficient low-cost millimeter-wave transmitters.