A 34.8%-PAE CMOS transmitter frontend for 24-GHz FMCW radar applications

A high-efficiency transmitter frontend circuit suitable for 24-GHz frequency-modulated continuous-wave (FMCW) radar applications is presented in this paper. In addition to the power amplifier (PA) stage, a voltage-controlled oscillator (VCO) is incorporated in the frontend for frequency modulation while a VCO buffer and a driving amplifier (DA) are utilized to provide an adequate driving level and reverse isolation. To take full advantage of the power available from the transistors, both the PA and DA stages are matched to the near-optimum impedances suggested by the load-pull simulation. Moreover, a positive-feedback technique is employed in the PA design for further efficiency enhancement. The proposed circuit is fabricated in a standard 90-nm CMOS process. Operated at a supply voltage of 1.2-V, the 24-GHz frontend demonstrates a peak power-added efficiency (PAE) of 34.8% with a peak output power of 16.3 dBm.