Light signal detecting circuit, light amount detecting device, and charged particle beam device
View Patent ↗A light signal detecting circuit, a light amount detecting device, and a charged-particle-beam device capable of discriminating the signal component of a small amount of light from the signal component of noise due to dark current. A data-processing-unit detects pulses from digital voltage signal corresponding to an amount of light obtained by an amplifier and an A-D converter, calculates a crest value as the maximum voltage value of each pulse, and stores the occurrence frequency of each calculated crest value in a frequency occurrence storage area. A data analysis unit compares a previously-determined frequency lower limit with the occurrence frequency of each crest value in ascending order of the crest values and sets a pulse determination threshold to the first crest value whose occurrence frequency is equal to or smaller than the frequency lower limit. The threshold processing unit thus outputs the digital signal higher than the pulse determination threshold.
1. A light signal detecting circuit, comprising:
amplifying means for amplifying an analogue detection signal corresponding to an amount of light detected by light detecting means;
analogue-to-digital converting means for converting the analogue detection signal amplified by the amplifying means to a digital detection signal;
threshold determination means for: repeating a process to detect a pulse from the digital detection signal obtained by the analogue-to-digital converting means and detect energy of the detected pulse; calculating an occurrence frequency of the pulses of each value of the energy; and determining a pulse determination threshold based on the calculated occurrence frequency of the pulses of each value of the energy; and
threshold processing means for outputting, as a detection signal, the digital detection signal including the pulses of the values of the energy not lower than the pulse determination threshold determined by the threshold determination means.
2. The light signal detecting circuit according to claim 1 , further comprising:
frequency count storing means for storing the occurrence frequency of the detected pulses of each value of the energy in association with the value of the energy, wherein
the threshold determination means includes:
data processing means for performing a process to store the occurrence frequency of the pulses of each value of the energy in the frequency count storing means; and
data analyzing means for sequentially comparing a previously determined frequency lower limit with the occurrence frequency of the pulses of each value of the energy, which is stored in the frequency count storing means, in ascending order of the value of the energy and for determining a pulse determination threshold to be the first value of the energy whose occurrence frequency of the pulses is equal to or lower than the frequency lower limit as the result of the comparison.
3. The light signal detecting circuit according to claim 1 , further comprising:
frequency count storing means for storing the occurrence frequency of the detected pulses of each value of the energy in association with the value of the energy, wherein
the threshold determination means includes:
data processing means for performing a process to store the occurrence frequency of the pulses of each value of the energy in the frequency count storing means; and
data analyzing means for sequentially comparing the occurrence frequency of the detected pulses of each value of the energy, which is stored in the frequency count storing means, in ascending order of the values of the energy to calculate the smallest occurrence frequency of the detected pulses and for determining a pulse determination threshold to be a value of the energy whose occurrence frequency of the pulses is equal to the calculated smallest occurrence frequency.
4. A light signal detecting circuit, comprising:
amplifying means for amplifying an analogue detection signal corresponding to an amount of light detected by light detecting means;
analogue-to-digital converting means for converting the analogue detection signal amplified by the amplifying means to a digital detection signal;
threshold determination means for: repeating a process to detect a pulse from the digital detection signal obtained by the analogue-to-digital converting means and detect energy of the detected pulse; calculating an occurrence frequency of the pulses of each value of the energy; and determining a pulse determination threshold based on the calculated occurrence frequency of the pulses of each value of the energy;
digital-to-analogue converting means for converting the pulse determination threshold determined by the threshold determination means from the digital signal to an analogue signal;
comparing means for determining whether the analogue detection signal corresponding to the detected amount of light is not smaller than the pulse determination threshold of the analogue signal converted by the digital-to-analogue converting means; and
counting means for counting and outputting the number of times when it is determined by the comparing means that the analogue detection signal corresponding to the detected amount of light is not smaller than the pulse determination threshold of the analogue signal obtained by the digital-to-analogue converting means.
5. The light signal detecting circuit according to claim 4 , further comprising:
frequency count storing means for storing the occurrence frequency of the detected pulses of each value of the energy in association with the value of the energy, wherein
the threshold determination means includes:
data processing means for performing a process to store the occurrence frequency of the pulses of each value of the energy in the frequency count storing means; and
data analyzing means for sequentially comparing a previously determined frequency lower limit with the occurrence frequency of the pulses of each value of the energy, which is stored in the frequency count storing means, in ascending order of the value of the energy and for determining a pulse determination threshold to be the first value of the energy whose occurrence frequency of the pulses is equal to or lower than the frequency lower limit as the result of the comparison.
6. The light signal detecting circuit according to claim 4 , further comprising:
frequency count storing means for storing the occurrence frequency of the detected pulses of each value of the energy in association with the value of energy, wherein
the threshold determination means includes:
data processing means for performing a process to store the occurrence frequency of the pulses of each value of the energy in the frequency count storing means; and
data analyzing means for sequentially comparing the occurrence frequency of the detected pulses of each value of the energy, which is stored in the frequency count storing means, in ascending order of the values of the energy to calculate the smallest occurrence frequency of the detected pulses and for determining a pulse determination threshold to be a value of the energy whose occurrence frequency of the pulses is equal to the calculated smallest occurrence frequency.
7. A charged particle beam device, comprising the light signal detecting circuit according to claim 1 .