Patent ID: 7952343

Claim:
Apparatus for measuring a current, comprising: a charge integrating circuit; a comparator circuit; and a logic circuit; wherein the charge integrating circuit is arranged to integrate charge from the current to be measured and apply a resulting change in voltage as an input to the comparator circuit; the comparator circuit is arranged to compare the input voltage with a threshold voltage level and provide an output responsive thereto to the logic circuit; the logic circuit is arranged to generate a feedback signal dependent upon the comparator output and to provide the feedback signal to the charge integrating circuit; the charge integrating circuit is further arranged to integrate charge from the received feedback signal in opposition to the integrating of the charge from the current to be measured; the logic circuit is further arranged to generate an output signal based upon the output from the comparator circuit and dependent upon the level of the current to be measured; the current to be measured removes charges from the charge integrating circuit, and the feedback signal adds charges to the charge integrating circuit; the amount of charge added to the charge integrating circuit by the feedback signal is a known amount; and the input voltage of the comparator circuit increases above the threshold voltage level when the feedback signal adds charges to the charge integrating circuit, and the output signal generated by the logic circuit comprises a pulse having a width dependent upon the time duration for the current to be measured to remove at least a portion of the known amount of charge added to the charge integrating circuit to reduce the input voltage of the comparator circuit to the threshold voltage level.