Abstract: In methods and apparatus for non-contact testing of an electronic circuit board at least one electromagnetic emission sensing probe is disposed a short distance from a circuit board under test, the circuit board is operated while sensing electromagnetic emission from a region of the circuit board near the probe, and a time domain representation of the sensed electromagnetic emission is developed. The time domain representation of the sensed electromagnetic emission is compared to a time domain representation of electromagnetic emission of a circuit board known to be operating properly. Preferably, an array of electric field sensing probes is used to sense emissions from several regions of the circuit board simultaneously, and time domain representations of the sensed electromagnetic emissions are simultaneously developed and compared to respective time domain representations of electromagnetic emissions from circuit boards known to be operating properly.

Abstract: The technique of measuring the duty cycle of a digital signal of known repetition rate is disclosed. It makes use of the fact that the probability of the digital signal being at the high level is related to its duty cycle when the signal is sampled at a frequency incoherent with the repetition rate. The apparatus in one embodiment includes a random sampler for sampling the digital signal under measurement, and digital counters which count the total number of samples and the number of samples whose values are at one of the two digital levels.

Abstract: In methods and apparatus for encoding a repetitive analog waveform as m n-bit digital words, p analog samples of the repetitive waveform are taken at each of m distinct sampling points, and q bits are derived from each distinct sample, where m, n, p and q are positive integers, p and q are less than n, and p.times.q=n. The methods and apparatus employ novel methods and apparatus for generating a pulse train having a precisely controlled duty cycle to define sampling times at which the samples are taken. The encoding methods and apparatus are useful for encoding high speed waveforms with relatively low speed circuitry.