Measuring illumination intensity by using photodiode - avoiding load dependency and nonlinearity by compensation of dark current during amplification

摘要

Aphotodiode is used and avoids the expensive amplification circuitry conventionally required for low photo voltage measurements. The difficulties associated with the load dependency of the photovoltage and the nonlinear relationship between photovoltage and illumination intensity are overcome. The photodiode is raised to a voltage within the characteristic field of the photodiode in a region of photocurrent practically independent of voltage. The rate of change of voltage as the photodiode discharges is measured essentially without consuming power. The voltage on the photodiode is amplified with a gain determined by the dark current. This achieves a compensation of the dark current content of the discharge current. Voltage rate of change is measured from the time taken to reach a given voltage.