Enlarging the Input Frequency Range of a Phase Noise Meter through Bandpass Sampling Strategies

Measurement of phase noise affecting oscillators or clocks is a fundamental practice whenever the need of a reliable time-base is of primary concern. In spite of the number of methods or techniques either available in literature or implemented as personalities in general purpose equipment, very accurate measurement results can be gained only from expensive, dedicated instruments. To offer a cost-effective alternative to dedicated instruments, the authors have already realized a DSP-based phase noise meter, capable of assuring high performance and real-time operation. The meter, however, suffers from a reduced analysis bandwidth (about 250 kHz) and needs an external time-base for input signal digitization. To overcome these drawbacks, the authors propose hereinafter the adoption both of bandpass sampling strategies and internal time-base. After some remarks on the previous version of the meter, key features of the adopted time-base and proposed sampling strategy are described in detail. Results of experimental tests, carried out on sinusoidal signals provided both by function and arbitrary waveform generators, are presented and discussed; evidence of the meter's reliability and efficacy is finally given.