A wide-range logarithmic charge digitizer

The digitizer described here accumulates charge from a measuring device and places it as the initial charge on the capacitor of an integrator. By measuring the time required for the charge on the capacitor to grow exponentially to a fixed threshold when positive feedback is applied, the circuit produces a digital output proportional to the logarithm of the ratio of the threshold charge to the initial charge. The digitizer includes correction for offsets and drifts in the electronics and in the measuring device, as well as compensation for the effects of dielectric absorption in the capacitor