Current to frequency converter - has short circuited photodiode connected to amplifier and driven from light pulses of known width and intensity

摘要

A current to frequency converter uses a charge/discharge technique controlled by a photo-diode. A short circuited Si photo-diode (Di), i.e. in the linear part of its characteristic, is connected to the amplifier (A1) and driven from light pulses of known width and intensity. The diode (D1) is unlit in the quiescent state. The output voltage (U1) is constant until the input current changes to (io). Then (Ui) increases until greater than (U2). The comparator (A2) then operates the pulse generator (G). This gives a pulse of width (T) which gives a known charge (TXif) via diode (D1) for current measurement. Voltage (U1) then reduces to below (U2) and the pulse generator is switched off. Pulse frequency (fo) is proportional to current for constant pulse width and intensity.