Built-In Self-Tests for 77GHz Radar Integrated Circuits

With the introduction of automotive radar in the 76 GHz-81 GHz band, a mass-market application in the millimeter-wave frequency range (30 GHz-300 GHz) has been established. For the first time, large numbers of very complex millimeter-wave integrated circuits are deployed. In this context, self-test of integrated circuits has become of interest. Testing every single chip with specialized measurement equipment is neither sensible nor cost-efficient when facing large volumes. Future safety-critical applications, such as autonomous driving, demand that the correct functionality of an integrated circuit is verified during its operation. Self-test is crucial in fulfilling this requirement. Based on the state of the art in millimeter-wave built-in self-test new components are developed that improve the accuracy of on-chip power measurement. The effectiveness of these components is demonstrated on the example of automotive radar in a silicon-germanium technology. Two differential power detectors, whose output does not depend on the common-mode component of the measured signal, are presented. Like all integrated components, power detectors are subject to process and temperature variations which significantly impact the achievable power measurement accuracy. To improve this accuracy, two calibration methods are developed: The first one is based on a purely analog circuit reducing the temperature-dependence of a power detector. In a second approach, digital post-processing is used to minimize both process and temperature variation. Directional couplers allow the connection of power detectors to the circuit under test without negative impact on the sensitive high-frequency interfaces. Two directional couplers with different coupling factors are implemented and characterized.