Mentor Graphics

PLLs are the heart of most SoCs, so their performance affects many tests. Practical, published PLL BIST approaches cannot measure <10 ps RMS jitter or >1 GHz. This paper describes how a SerDes undersampling DFT technique was adapted to test multiple PLLs and DLLs for jitter, phase error, output frequency, duty cycle, lock time, and lock range. Two techniques for canceling random and systematic noise are also described. The multi-GHz range, subpicosecond jitter noise floor, and minimal silicon area are better than for any previous silicon-proven DFT or BIST that needs no calibration or analog circuitry. FPGA implementation results are provided.