A compact mobile FM Transmitter with automatic embedded antenna tuning and low spurious emission in 65nm CMOS

Abstract

A 76-108MHz FM Transmitter emits 120dBμVrms output signal using an embedded antenna on a PCB. A proposed on-chip calibration scheme digitally tunes an on-chip capacitor array to centre the embedded antenna resonance circuit with an external inductor at the desired FM channel. The transmitter achieves a 60dB audio SINAD, better than -45dB LO leakage and -50dB sideband suppression with -30/-55dB ACLR for 200kHz/400kHz offsets, respectively. The out of band spurious emission level for coexistence with other radio bands is very low and mostly around -102 dBm or less. A new on-chip T/R switch capable of handling 4Vpp signal is used to allow both FM TX and RX to share the same embedded antenna. The transmitter adds only 0.2mm^2 die area overhead to an FM TRX SoC in 65nm CMOS and draws 10mA from a 4.2V battery.