A 28 nm CMOS Dual-Band Concurrent WLAN and Narrow Band Transmitter With On-Chip Feedforward TX-to-TX Interference Cancellation Path for Low Antenna-to-Antenna Isolation in IoT Devices

A dual-band, concurrent 2.4G wireless local-area network (WLAN) and 2.4G narrow band (NB) transmitter (TX) with on-chip feedforward TX-to-TX interference cancellation path for low antenna-to-antenna isolation in internet of things (IoT) devices is proposed. The on-chip cancellation path generates a replica signal of the same magnitude but 180° out-of-phase with respect to the “aggressor” TX signal appearing at the “victim” TX output. An on-chip third-order intermodulation distortion (IMD3) calibration engine carries out the cancellation calibration across all channel combinations in NB and WLAN using an over-the-air antenna-to-antenna channel, and the measured IMD3 product is reduced by 25 dB. Additionally, the maximum output power during concurrent transmission, while meeting the FCC out-of-band emission specification, improves from 10 to 17 dBm across all WLAN channels in a certified FCC out-of-band emission test. With this proposed architecture, the issue of TX-to-TX interference in multiradio coexistence is finally addressed, opening the door to future high-power concurrent multiband TXs in reconfigurable IoT devices.