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

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.