A 79 GHz SiGe Doherty Power Amplifier Suitable for Next-Generation Automotive Radar

The number of environment-detecting sensors inside cars continuously increases, to enable failsafe autonomous driving. With more sensors, the probability of performance degrading interferences increases. A promising solution to the interferences is orthogonal frequency division multiplex (OFDM) radar. Due to the complex modulation scheme, the analog front end, especially the power amplifier in the transmitter, has to deal with a high peak-to-average power ratio. Therefore, conventional amplifiers have to be operated in power back-off to maintain linear operation at the drawback of reduced power-added efficiency. To mitigate this problem, a Doherty power amplifier for an automotive radar transceiver is proposed. In this work, we present a design methodology for an integrated Doherty amplifier for automotive radar applications, focussing on the theory of operation by analyzing transistor-level simulations. Small- and large signal simulations analyze the concept of load modulation for a Doherty amplifier in the automotive frequency band from 76--81 GHz. Using a fully differential transmission-line-based approach, we showcase the superior performance of an automotive Doherty amplifier over an conventional state-of-the-art reference amplifier. In measurements, the proposed Doherty amplifier achieves a saturated output power of 17.2 dBm with a peak power-added efficiency of 11.6%. When operating in 6 dB back-off, the PAE still amounts to 6.1%. Thereby we propose to improve conventional automotive power amplifiers by incorporating them into a Doherty amplifier.