US3843880A - Illumination-to-voltage conversion apparatus - Google Patents

Illumination-to-voltage conversion apparatus Download PDF

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Publication number
US3843880A
US3843880A US00411341A US41134173A US3843880A US 3843880 A US3843880 A US 3843880A US 00411341 A US00411341 A US 00411341A US 41134173 A US41134173 A US 41134173A US 3843880 A US3843880 A US 3843880A
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United States
Prior art keywords
photoconductive element
transistor
voltage
controlling means
series
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Expired - Lifetime
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US00411341A
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English (en)
Inventor
K Tsuchiyasu
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Minolta Co Ltd
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Minolta Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/44—Electric circuits

Definitions

  • the apparatus is constituted by connecting a first controlling means t1 for current controlling in series to a photoconductive element Rp having non-linear characteristic of Rp K E, where Rp is resistance, E is luminous intensity and K and 'y are constants, and by connecting a second controlling means t2 so as to receive a voltage Vp across both ends of the photoconductive element Rp and to give a signal, which is approximately proportional to Vp of said first controlling means t1, which controls the current Ip of the photoconductive element Rp to be approximately proportional to the value E and as a result causes the voltage Vp to be approximately in inverse proportion to the luminous intensity E.
  • the resistance of a photoconductive element is not in exact inverse proportion to the luminous intensity, but has the following relationship:
  • Vp K E Ip Hitherto among actual apparatus requiring that an output be in exact inverse proportion to the luminous intensity, an apparatus constituted as shown in FIG. 1, wherein logarithm-transforming means such as, a logarithm-compressor circuit and a logarithm-expander circuit, is employed.
  • logarithm-transforming means such as, a logarithm-compressor circuit and a logarithm-expander circuit
  • a photoconductive element Rp is connected to a constant current source CIS so that a constant current flows through the photoconductive element Rp.
  • the voltage Vp across the element Rp is and is given to a logarithmic-compressor circuit LCC to produce the following output:
  • the abovementioned prior art apparatus has the shortcoming of having a low signal-to-noise (S/N) ratio, since noises mixed at points a or b in FIG. 1, which points are in a prior stage to the stage for the logarithmic-expansion by the circuit LEC, are expanded to a great extent by the expansion, resulting in poor signalto-noise ratio in the output voltage V. Hitherto, a circuit of very complicated configuration was necessary to eliminate such expansion of the noise.
  • S/N signal-to-noise
  • This invention purports to provide an apparatus capable of attaining good S/N ratio in transforming luminous intensity to voltage with good linearity characteristic, by employing rather simple circuit constitution.
  • FIG. 1 is a schematic block diagram showing the above-mentioned conventional apparatus for transforming luminous intensity to voltage
  • FIG. 2 is a schematic block diagram showing the fundamental construction of the apparatus of the present invention.
  • FIG. 3 is a graph showing the relationship between the input voltage and the output voltage of the second controlling means of FIG. 2;
  • FIG. 4 is a schematic circuit diagram showing the fundamental circuit configuration of an apparatus embodying the present invention.
  • FIG. 5 is a schematic circuit diagram showing one actual example of the apparatus embodying the present invention.
  • FIG. 6 is a schematic circuit diagram showing a circuit equivalent to the circuit of FIG. 5.
  • FIG. 7 is a graph showing the relationship between the relative input luminous intensity and therelative output current flowing through the photoconductive element.
  • the apparatus of the present invention has a fundamental configuration as shown in FIG. 2, wherein a photoconductive element Rp and a first controlling means t1, which controls the current of the element Rp, are connected in series across a DC. power source DCS, and both ends of the photoconductor element Rp are connected to input terminals of a second controlling means t2 which applies a controlling signal to the first controlling means :1.
  • the first controlling means :1 controls the current Ip of the element Rp in proportion to its control input voltage Y received from the output of the second controlling means t2.
  • the second controlling means t2 receives as an input voltage the voltage Vp across both ends of the element Rp.
  • the output terminals Out are connected to respective ends of the photoconductive element Rp.
  • the first controlling means :1 controls its output current 1p so as to be proportional to the output K3 E of the second controlling means, and therefore, the voltage Vp across both ends of the photoconductive element Rp, namely, the voltage at the output terminal OUT of this apparatus corresponds to the equation (3.1).
  • the characteristic of the equation (3.2) is the theoretical characteristic, which is shown by a solid curve in the graph of FIG. 3. However, it has been difficult to attain such a characteristic by means of a simple circuit. However, in practical operation, the abovementioned characteristic can be approximated by the following characteristic if constants are properly selected:
  • FIG. 4 A preferred fundamental example embodying the present invention is shown in FIG. 4, wherein details of the first and the second controlling means :1 and :2 are shown.
  • the first controlling means comprises a first transistor T1, the collector of which is connected to one end of the photoconductive element Rp.
  • the second controlling means :2 comprises a second transistor-T2, the base and the emitter of which are connected across both ends of the photoconductive element Rp, and to the collector of which are connected a diode D and a variable resistor R2 in series.
  • the junction point p between the collector of the second transistor T2 and the diode D is for logarithmic-conversion and is connected to the base of the first transistor T1.
  • FIG. 5 shows a more practical embodiment provided with two variable resistors R2 and Rv as characteristicapproximation adjusting means.
  • the apparatus also provides a pair of thermistois H1 and H2 for temperature compensation, a current adjusting transistor Q3 and a shunt resistor Bs.
  • a Darlington connection consisting of a pair of transistors Q1 and Q2is employed in place of the second transistor T2, in order that only very little input current to the base of the transistor Q1 is required.
  • the transistor Q3 is provided connecting its collector, emitter and base to the positive end of the DC source, one end of the photoconductive element Rp, and a moving arm of the variable resistor Rv, respectively.
  • variable resistor Rv is for adjusting the curve for good approximation in the high luminous intensity range
  • variable resistor R2 is for adjusting the curve for good approximation in the low luminous intensity range
  • a series connectionof several diodes may be employed in place of the diode D to ensure higher reverse breakdown voltage.
  • the circuit of FIG. 5 can be represented by the equivalent circuit of FIG. 6.
  • the dotted curve indicates the experimental result of the circuit of FIG. 5.
  • the curve in the left and right parts are adjusted by the variable resistors R2 and Rv, respectively.
  • the variable resistors R2 and Rv can be well approximated to the solid line.
  • the apparatus of the present invention has a low noise level for the following reason:
  • Vp R21 dlog i Namely, the output voltage Vp consists of a first part which is proportional to the current i and a second part which is a logarithmic compression of the current i.
  • a noise, Le a small fluctuation in the current 1', makes a resultant noise, i.e., a small fluctuation in the voltage Vp.
  • Such a resultant noise consists of a first part originated from the first part R2 -i, i.e., a proportional part, and of a second part d log i, i.'e., a logarithmic compressed part; and therefore, the resultant noise is no greater than the conventional logarithmic expanded noise as explained with reference to FIG. 1.
  • Illumination-to-voltage conversion apparatus comprising:
  • first controlling means connected in series with said photoconductive element across said direct current source for controlling the current flowing through said photoconductive element
  • second controlling means connected to receive as an input signal the voltage appearing across bothends of said photoconductive element and producing an output signal for controlling said first controlling means to regulate the current through said photoconductive element to be approximately proportional to the 1 'yth power of said voltage appear-- ing across said photoconductive element, and a means for taking out as an output signal the voltage across both ends of the photoconductive element.
  • trode which is connected in series to at least one diode for logarithmic transformation and a variable resistor, the base and emitter electrodes of said first transistor being connected across the series combination of said diode and said variable resistor, and the base and emitter electrodes of said second transistor being connected across said photoconductive element.
  • the apparatus of claim 3 further including a third transistor connected in series with said photoconductive element, the base and emitter electrodes of said second transistor being connected across the series combination of said photoconductive element and said third transistor, the base electrode of said third transistor being connected to a source of referencevoltage.
  • said second controlling means comprises two second transistors connected in series in a Darlington configuration and connected across said direct current source.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)
  • Networks Using Active Elements (AREA)
  • Tone Control, Compression And Expansion, Limiting Amplitude (AREA)
US00411341A 1972-10-31 1973-10-31 Illumination-to-voltage conversion apparatus Expired - Lifetime US3843880A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP10928172A JPS5520176B2 (enrdf_load_stackoverflow) 1972-10-31 1972-10-31

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US (1) US3843880A (enrdf_load_stackoverflow)
JP (1) JPS5520176B2 (enrdf_load_stackoverflow)
DE (1) DE2354212A1 (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4100407A (en) * 1976-06-28 1978-07-11 Nippon Electric Co., Ltd. Photoelectric conversion circuit
US4516020A (en) * 1982-12-28 1985-05-07 The United States Of America As Represented By The United States Department Of Energy Light-operated proximity detector with linear output
US4682022A (en) * 1985-02-21 1987-07-21 The Perkin-Elmer Corporation Detector preamplifier for use with a MCT detector
US6642500B2 (en) * 2000-02-01 2003-11-04 Canon Kabushiki Kaisha Signal processing apparatus which performs logarithmic compressions

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6290967A (ja) * 1985-10-17 1987-04-25 Nissan Motor Co Ltd 受光用半導体集積回路
WO1995005225A1 (en) * 1993-08-17 1995-02-23 Ludvik Zeman A wind powered toy wheel

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3194968A (en) * 1962-09-20 1965-07-13 George F Masin Photodetector circuit for the detection of weak radiant signals in the presence of a large signal background

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3194968A (en) * 1962-09-20 1965-07-13 George F Masin Photodetector circuit for the detection of weak radiant signals in the presence of a large signal background

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4100407A (en) * 1976-06-28 1978-07-11 Nippon Electric Co., Ltd. Photoelectric conversion circuit
US4516020A (en) * 1982-12-28 1985-05-07 The United States Of America As Represented By The United States Department Of Energy Light-operated proximity detector with linear output
US4682022A (en) * 1985-02-21 1987-07-21 The Perkin-Elmer Corporation Detector preamplifier for use with a MCT detector
US6642500B2 (en) * 2000-02-01 2003-11-04 Canon Kabushiki Kaisha Signal processing apparatus which performs logarithmic compressions

Also Published As

Publication number Publication date
DE2354212A1 (de) 1974-05-09
JPS5520176B2 (enrdf_load_stackoverflow) 1980-05-31
JPS4968780A (enrdf_load_stackoverflow) 1974-07-03

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