System Level Verification of Phase-Locked Loop using Metamorphic Relations

In this paper we build on Metamorphic Testing(MT), a verification technique which has been employed very successfully in the software domain. The core idea is to uncover bugs by relating consecutive executions of the program under test. Recently, MT has been applied successfully to the verification of Radio Frequency (RF) amplifiers at the system level as well. However, this is clearly not sufficient as the true complexity stems from Analog/Mixed-Signal (AMS) systems. In this paper, we go beyond pure analog systems, i.e. we expand MT to verify AMS systems. As a challenging AMS system, we consider an industrial PLL. We devise a set of eight generic Metamorphic Relations (MRs). Theses MRs allow to verify the PLL behavioral at the component level and at the system level. Therefore, we have created MRs considering analog-to-digital as well as digital-to-digital behavior. We found a critical bug in the industrial PLL which clearly demonstrates the quality and potential of MT for AMS verification.