Multi-scheme PSK and QAM modulator through vector scaling and summation

A 5.4 GHz direct-digital modulator capable of producing both PSK and QAM modulation schemes is presented. The circuit uses a vector summing approach in which variable-gain OTAs are used to scale the vectors. Vector summation occurs in the current domain and 4-PSK, 8-PSK, 4-QAM and 16-QAM modulation formats are demonstrated. Measurement results on the fabricated circuit show that the highest developed EVM is 8.51% for the 8-PSK modulation scheme. The chip was fabricated at 130 nm-CMOS technology and the chip area occupies 0.09 mm². The circuit consumes 13 mA and operates at the standard 1.2 V supply for a 130 nm process.