Device and method for the measurement of electric quantities using analog-to-digital converters (ADC)
Data di pubblicazione
Data di priorità
Patent application in Europe and US
Politecnico di Milano
Department of Electronics, Information and Bioengineering
Giorgio Ferrari, Giacomo Gervasoni, Marco Carminati, Filippo Campoli
The invention consists in a novel technique to compensate slow random fluctuations of the gain in a data acquisition chain based on an analog-to-digital converter (ADC). Examples of gain fluctuation sources are the ADC voltage reference or the low-frequency noise of components inside the ADC. The random fluctuation of the gain introduces an uncertainty in the conversion, which limits the smallest signal variation (resolution) detectable by the acquisition chain. The invention reduces the effect of these fluctuations thanks to a digital processing of the signals coming from two acquisition channels (not necessarily identical) which alternately acquire a reference signal and the signal under investigation. The time evolution of the two signals time is reconstructed and their amplitude is evaluated in the digital domain. Since the random fluctuation of the gain has the same effect on the two calculated amplitudes, the ratio between the two averaged amplitudes (signal under investigation and reference signal) allows a reduction of the effects of slow gain fluctuations and accordingly enhances the resolution of the measurement. Although limitations occur, the invention can be implemented using a single ADC connected alternatively to the signal under investigation and to the reference signal.
Campo di applicazione
The invention is suitable for applications where an ultra-high resolution measurement of the amplitude of an electrical signal (slowly varied or modulated) is required. In particular, the technique allows an enhancement in terms of maximum resolution achievable with a digital lock-in amplifier, an instrument extensively used for the measurement of periodic signals (amplitude and phase).
The invention enhances the maximum resolution achievable by an acquisition system allowing ultra-high resolution (better than 1 ppm). It can enhance the performance of acquisition systems that for cost or technological reasons (for example due to the high frequency of operation) have high random fluctuations of the gain.
The main advantage of the novel technique is the capability to acquire electrical signals with enhanced resolution compared to the standard analog/digital acquisition chain. The enhancement in terms of maximum resolution is given by the reduction of the slow gain fluctuations in the analog/digital acquisition chain. The technique works also with modulated signals. In the case of implementation of a lock-in amplifier, a resolution enhancement of a factor 58 with respect to a commercial instrument has been demonstrated.
Differently from the conventional differential approach, this novel technique does not need the generation of a reference signal ideally identical to the signal to be measured, thus our device operates without calibration and without limitations over the working frequency span.
Stadio di sviluppo