Contactless testing of on-chip oscillator operation

The on-chip oscillator operation can be verified in a contactless way if the oscillator tank inductance is also used as a transmitting antenna. When the probing (receiver) antenna located on the test head is close to the oscillator, both antennas together may be considered as a transformer. The receiving antenna moving to and from the oscillator disturbs the oscillation frequency and amplitude, and these disturbances are registered by the measuring device connected to the receiving antenna. These disturbances, which are not occurring in ordinary oscillators with constant components, are evaluated using the equivalent circuit of thus formed transformer. The variation of frequency and the primary and secondary amplitudes as functions of distance between antennas are calculated. The results are experimentally verified with the oscillator realized in 0.13 μm CMOS technology.