Test measures evaluation for VCO and charge pump blocks in RF PLLs

Abstract

This work deals with the development of test techniques for RF (Radio Frequency) components. The optimization of production tests for RF PLLs (Phase Locked Loops) is targeted in particular. With devices of ever increasing speed, it is no longer possible to measure some of the classical circuit performances even with dedicated RF testers. This problem has been tackled in recent years by using BIST (Built-In Self Test) techniques for PLLs able to perform on-chip high resolution measurements such as picosecond jitter. However, this risks to become also impossible at very high frequencies.This paper will present some preliminary work towards the optimization of production tests for RF PLLs with the aim of avoiding traditional test measurements such as phase noise. Attention will be focused on single relevant blocks of the RF PLL that have the greatest impact on phase noise and other critical performances. The VCO (Voltage Controlled Oscillator) block will be first studied, since it gives the greatest contribution to phase noise. Our work will proceed by taking into consideration the possibility to detect mismatches and leakages in CP (Charge Pump) currents that cause spurious in the output spectrum. Simulation results in this paper will consider only catastrophic faults in circuit components. The fault coverage of performances and simple test measurements that can be implemented on-chip for the VCO is thus evaluated.