Analysis and Design of Reactive Passive Mixers for High-Order Modulation IoT Cartesian Transmitters

The growth of the Internet of Things (IoT) is calling for more efficient, higher data rate radios. However, the high-order modulations required to push the data rates, while increasing the spectral efficiency, clash with the transmitter (TX) power efficiency, as they require more complex and more linear systems. An unconventional quadrature modulator, based on reactive passive mixers, is proposed as the key building block to simplify the signal path of a Cartesian TX and achieve a performance comparable to a polar architecture while enabling the use of more complex modulation formats. A proof-of-concept Cartesian TX, based on the proposed reactive quadrature modulator, and implemented in a 22-nm fully depleted silicon on insulator (FD-SOI) CMOS technology, is capable of generating a 16-QAM-modulated signal at 2.4-Mbaud symbol rate with a 2.7-dBm average output power and
$\text {error vector magnitude} \text {(EVM)} = -24.5$
dB,
$\text {ACLR} = -32$
dBc, and
$P_{\mathrm{ alt}}= -36$
dBm, while showing a 22% system efficiency.