This paper presents a novel multifunctional test structure called Analog BulLt-in Block Observer (ABILBO). This structure is based on analog integrators and achieves analog scan, test frequency generation and test response compaction. A high fault coverage was obtained by using a discrete switched-capacitor ABILBO for testing a biquad filter. The ABILBO area overhead and performance penalty can be very low if functional and testing circuitry are shared. This is typically the case of high order filters based on a cascade of biquads