Mixed domain spectrum measurement method
AssigneeHewlett-Packard Company
InventorDouglas R. Wagner
Life of this patent
Estimating the term…
Abstract
Aliasing and synchronization difficulties in determining transfer functions in mixed domain (analog and digital) systems are overcome by sampling the analog signal at a higher sampling frequency that the digital signal, and zero filling the set of sampled digital data (if necessary) so that the sampled digital data corresponds to the more densely sampled analog data. By so doing, a single fixed frequency anti-alias filter in the analog channel can be used to avoid aliasing problems in mixed domain measurements over any span of frequencies, up to the entire passband of the filter. The invention is particularly illustrated with reference to measurements both across digital-to-analog boundaries and across analog-to-digital boundaries.
Claims17
A method of characterizing a response of a mixed domain system to an input signal by using a single measurement instrument, the mixed domain system having both an analog signal and a digital signal, the measurement instrument characterizing the spectral composition of a signal by a Fourier transform method that generates spectral coefficients accumulated in a plurality of data bins, each of said bins corresponding to a particular frequency in a spectrum, the method comprising:
- stimulating the mixed mode system with an input signal;
- sampling the analog signal in the mixed mode system at a first sampling frequency F.sub.1 using a first sampling clock signal;
- processing the sampled analog signal in the measurement instrument to obtain a spectral representation thereof, said spectral representation comprising a first set of coefficient data accumulated in data bins;
- sampling the digital signal at a second sampling frequency F.sub.2 using a second sampling clock signal;
- processing the sampled digital signal in the measurement instrument to obtain a spectral representation thereof, said spectral representation comprising a second set of coefficient data accumulated in data bins;
- and
- comparing the first set of coefficient data with the second set of coefficient data to determine a transfer function of the mixed domain system;
- wherein the first and second sampling clock signals are phase locked but do not have coincident zero crossings.
A method of making measurements on a mixed domain system with a single measurement instrument, the mixed domain system having both an analog signal and a digital signal, the digital signal comprising a plurality of binarily weighted data bits representing the amplitude of a signal, the measurement instrument characterizing the spectral composition of a signal by a Fourier transform method that generates spectral coefficients accumulated in a plurality of data bins, each of said bins corresponding to a particular frequency in a spectrum, the method comprising:
- sampling the analog signal at a first sampling frequency F.sub.1 ;
- processing the sampled analog signal in the measurement instrument to obtain a spectral representation thereof, said spectral representation comprising a first set of coefficient data accumulated in data bins;
- sampling the digital signal at a second sampling frequency F.sub.2 ;
- processing the sampled digital signal in the measurement instrument to obtain a spectral representation thereof, said spectral representation comprising a second set of coefficient data accumulated in data bins;
- and
- comparing the first set of coefficient data with the second set of coefficient data to determine a transfer function of the mixed domain system;
- wherein the first and second sampling frequencies are different.
A method of making measurements on a mixed domain system with a measurement instrument over a frequency span F.sub.span, said system and instrument comprising an analog signal source, a low pass filter having a cutoff frequency F.sub.LP having an input coupled to the analog signal source and an output coupled to a sampling circuit, said sampling circuit having a sampling frequency F.sub.s analog, the system and instrument further comprising an analog-to-digital converting circuit element and a digital sampling circuit having a sampling frequency F.sub.s digital coupled thereto, the method comprising:
- setting a ratio between f.sub.s analog and F.sub.s digital to be greater than a limit K, where K is defined by the formula:
- K=(F.sub.span +F.sub.LP)/F.sub.s digital.
Dependencies are inferred from the claim text.