A novel built-in current integrator (BICI) is proposed for measuring the average supply current (IDD) of embedded circuit blocks. Such a circuit can be used both as a current signature generator and power monitor. The BICI uses only small capacitors (total 72 pF), a simple comparator, 7 switches, and a counter to perform integration over a long time (1 ms) window and digitize IDD. The BICI generates a digital signature proportional to IDD and occupies a small area which make it suitable for BIST applications on mixed-signal ICs. The circuit has been implemented using a standard 0.5 _ CMOS technology. Circuit performance trade-offs are analyzed and optimization guidelines provided. Simulation results are also included.