| 摘要 |
1532262 Avalanche photo-diode circuit FERRANTI Ltd 31 March 1977 [3 April 1976] 13620/76 Heading G1A A photo-diode circuit has an avalanche photodiode D 1 with a positive temperature coefficient of breakdown voltage connected to an electrical supply with the P-N junction reverse biased by a voltage determined by limiting means Z 1 , Z 2 , Z 3 , Z 4 , changeable between two values, the higher equal to its breakdown voltage at a desired operating temperature, the detection of radiation taking place after changing to the lower voltage, the P-N junction being substantially at the desired operating temperature. The output from D 1 is via amplifier A 1 , shunt diode D 2 becoming forward biased when the current is excessive. The higher and lower reverse bias voltages are determined by Zener diodes Z 1 , Z 2 , Z 3 , Z 4 and Z 1 , Z 2 , Z 3 respectively. A sawtooth waveform Fig. 3 (not shown) is applied to the circuit of Fig. 4 with a peak rectifier charging large capacitor C 1 to the lower voltage across Z 1 , Z 2 , Z 3 . Smaller capacitor C 2 charges to the larger voltage. When the supply voltage is switched to zero, C 2 is discharged to acquire the lower voltage of C 1 . In Figs. 5 and 7 (not shown) the limiting means is a voltage regulator. Ways are shown of protecting D 1 from prolonged excessive radiation. In one method in Fig. 4 an auxilliary non-avalanche photo-diode D 1 ' operates a by-pass means 40. |
