^4fPrecise and high speed input capacitance measurement for semiconductors used in contactless smart cards

摘要

^7fRFID IC's used in contactless Smart Card applications represent an emerging technology in Europe and Asia. Contactless Smart Cards already exist in a large variety of applications such as public transportation cards (Shanghai Public Transportation Card), ID cards, pricing labels and baggage tags. In the card assembly, the input capacitance of the IC and the inductance of the antenna coil, constitute a resonating circuit at 13.56MHz, which represents the most commonly used frequency for contactless Smart Card applications. The input capacitance of these ICs is usually in the range of 20pF-100pF and it is most critical to ensure the correct value during production test. But a precise capacitance measurement in the range mentioned requires expensive and dedicated instrumentation. This paper presents a solution that solves the outlined problem by describing a precise and fast method for capacitance measurement. Based on a voltage/current phase shift technique, suited for implementation with common AC instrumentation, the solution can be used with today's ATE test systems.