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S4584-06 Datasheet(PDF) 7 Page - List of Unclassifed Manufacturers |
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S4584-06 Datasheet(HTML) 7 Page - List of Unclassifed Manufacturers |
7 / 16 page 4 The photocurrent produced by a given level of incident light varies with the wavelength. This relation between the photoelectric sensitivity and wavelength is referred to as the spectral response characteristic and is expressed in terms of photo sensitivity, quantum efficiency, etc. The quantum efficiency is the number of electrons or holes that can be detected as a photocurrent divided by the number of the incident photons. This is commonly expressed in percent (%). The quantum efficiency and photo sensitivity S have the following relationship at a given wavelength (nm): λ: Wavelength (nm) S: Photo sensitivity at wavelength λ (A/W) 1. Spectral response This measure of sensitivity is the ratio of radiant energy expressed in watts (W) incident on the device, to the re- sulting photocurrent expressed in amperes (A). It may be represented as either an absolute sensitivity (A/W) or as a relative sensitivity normalized for the sensitivity at the peak wavelength, usually expressed in percent (%) with respect to the peak value. For the purpose of our PSD data sheets (separately available), the photo sensitivity is represented as the absolute sensitivity, and the spec- tral response range is defined as the region in which the relative sensitivity is higher than 5 % of the peak value. 2. Photo sensitivity: S QE = × 100 [%] S × 1240 λ This is the resistance between opposing electrodes in a dark state. The interelectrode resistance is an important factor that determines the response speed, position res- olution and saturation photocurrent. The interelectrode resistance is measured with 0.1 V ap- plied across the opposing electrodes and the common electrode left open. When measuring the interelectrode re- sistance of two-dimensional PSDs, the output electrodes other than the opposing electrodes under measurement are left open. 7. Interelectrode resistance: Rie When a reverse voltage is applied to a PSD, a slight cur- rent flows even in a dark state. This is termed the dark current and is a source of noise. The dark current listed in our PSD data sheets (separately available) are the total dark current values measured from all output electrodes. 8. Dark current: ID A capacitor is formed at the PN junction of a PSD and its capacitance is called the junction capacitance. The ter- minal capacitance is the sum of the junction capacitance plus the package stray capacitance, and is a factor in determining the response speed. The terminal capaci- tance listed in our PSD data sheets are the total capaci- tance values measured from all output electrodes. 9. Terminal capacitance: Ct The rise time is defined as the time required for the PSD output to rise from 10 to 90 % of the steady output level, when a step function light is input to the PSD. The rise time depends on the incident light wavelength, load resistance, light incident position and reverse voltage, and is measured under the following conditions. · Light source : λ=890 nm · Incident spot light : φ1 mm · Incident light position: Center point of PSD · Load resistance : 1 k Ω (connected to all output electrodes) 10. Rise time: tr This is the maximum photocurrent value obtained from a PSD as long as it still functions as a position sensor. This value depends on the reverse voltage and interelec- trode resistance, and is defined as the total photocurrent when the entire active area is illuminated. 11. Saturation photocurrent: Ist Increasing the reverse voltage applied to a PSD can cause it to breakdown at a certain level and result in se- vere deterioration of PSD performance. To avoid this, the maximum reverse voltage is specified as the abso- lute maximum rating (this value must not be exceeded even momentarily) at a reverse voltage somewhat lower than the breakdown voltage. 12. Maximum reverse voltage: VR Max. 3. Quantum efficiency: QE If a light beam strikes the electrical center of a PSD, the sig- nal currents extracted from the output electrodes are equal. When this electrical center is viewed as the origin, the posi- tion detection error is defined as the difference between the position at which the light is actually incident on the PSD and the position calculated from the PSD outputs. Measure- ment conditions for position detection error are as follows: Light source : λ=890 nm Incident spot light: φ200 µm Photocurrent : 10 µA 5. Position detection error This is the minimum detectable displacement of a spot light incident on a PSD, and is expressed as a distance on the PSD surface. Resolution is mainly determined by the S/N and given by “resistance length × noise / signal”. The resolution values listed in our PSD data sheets (separately available) are calculated based on the RMS values for noise measured under the following conditions. · Interelectrode resistance: Typical value (listed in the data sheets) · Photocurrent : 1 µA · Frequency bandwidth : 1 kHz · Equivalent noise input voltage to circuit: 1 µV 6. Position resolution: ∆R This is the distance between electrodes on a PSD and is used to calculate the position from the PSD outputs. The resistance length is equivalent to the active area size, except for the pin-cushion type (improved tetra-lateral type) whose resistance length is expressed by the distance actually used to calculate the position. 4. Resistance length: L Description of terms |
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