Illuminance sensor determining the duty ratio of a PWM signal based on a digital output of an A/D converter and light control apparatus
First Claim
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1. An illuminance sensor, comprising:
- light receiving means for outputting an electric signal corresponding to ambient brightness;
A/D conversion means for converting the electric signal output from the light receiving means into a digital signal;
duty ratio determination means including;
an illuminance register storing the digital signal output from the A/D conversion means; and
duty ratio registers each storing a duty ratio which is output based on a value of the illuminance register, the duty ratio determination means determining the duty ratio of a PWM signal based on the digital signal output from the A/D conversion means; and
PWM signal output means for outputting the PWM signal based on the duty ratio output from the duty ratio determination means,the illuminance sensor further comprising;
(a) light receiving signal logarithmic compression means for logarithmic-compressing the electric signal which is output from the light receiving means and outputting the electric signal as a voltage;
(b) temperature compensation means having same temperature characteristic as the light receiving means;
(c) temperature correction signal logarithmic compression means for logarithmic-compressing the electric signal which is output from the temperature compensation means and outputting the electric signal as a voltage;
(f) offset voltage output means for outputting an offset voltage which is a sum of a reference voltage and a voltage calculated by multiplying a thermal voltage by a constant; and
(g) potential difference output means for outputting, as an analog signal, a difference between (i) a voltage which is a sum of a voltage outputted by the temperature correction signal logarithmic compression means and the offset voltage outputted by the offset voltage output means and (ii) a voltage outputted by the light receiving signal logarithmic compression means,the A/D conversion means including;
(d) D/A conversion means being included in the A/D conversion means and re-converting the digital signal which is output from the A/D conversion means into an analog signal;
(e) analog signal comparison means for comparing (i) a magnitude of the analog signal which is output from the potential difference output means with (ii) a magnitude of the analog signal which is output from the D/A conversion means being included in the A/D conversion means and re-converting the digital signal which is output from the A/D conversion means into an analog signal, and outputting a digital signal control signal for controlling the digital signal output from the A/D conversion means in such a way as to equalize the magnitudes of the analog signals; and
(h1) an illuminance level updown counter for increasing or decreasing a value of the digital signal which is output therefrom, based on the digital signal control signal (i) which is output from the analog signal conversion means, and (h2) converting the digital signal into a digital signal which is output from the A/D conversion means;
(i) the analog signal which is output from the D/A conversion means being a sum of the reference voltage and a voltage calculated by multiplying the thermal voltage by a variable.
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Abstract
The following members are included: a light receiving element which outputs an electric signal corresponding to ambient light; an A/D converter which converts the electric signal output from the light receiving element into a digital signal; a register which stores the digital signal output from the A/D converter and determines the duty ratio of a PWM signal based on the digital signal; and a PWM controller which outputs the PWM signal based on the duty ratio output from the register.
10 Citations
12 Claims
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1. An illuminance sensor, comprising:
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light receiving means for outputting an electric signal corresponding to ambient brightness; A/D conversion means for converting the electric signal output from the light receiving means into a digital signal; duty ratio determination means including;
an illuminance register storing the digital signal output from the A/D conversion means; and
duty ratio registers each storing a duty ratio which is output based on a value of the illuminance register, the duty ratio determination means determining the duty ratio of a PWM signal based on the digital signal output from the A/D conversion means; andPWM signal output means for outputting the PWM signal based on the duty ratio output from the duty ratio determination means, the illuminance sensor further comprising; (a) light receiving signal logarithmic compression means for logarithmic-compressing the electric signal which is output from the light receiving means and outputting the electric signal as a voltage; (b) temperature compensation means having same temperature characteristic as the light receiving means; (c) temperature correction signal logarithmic compression means for logarithmic-compressing the electric signal which is output from the temperature compensation means and outputting the electric signal as a voltage; (f) offset voltage output means for outputting an offset voltage which is a sum of a reference voltage and a voltage calculated by multiplying a thermal voltage by a constant; and (g) potential difference output means for outputting, as an analog signal, a difference between (i) a voltage which is a sum of a voltage outputted by the temperature correction signal logarithmic compression means and the offset voltage outputted by the offset voltage output means and (ii) a voltage outputted by the light receiving signal logarithmic compression means, the A/D conversion means including; (d) D/A conversion means being included in the A/D conversion means and re-converting the digital signal which is output from the A/D conversion means into an analog signal; (e) analog signal comparison means for comparing (i) a magnitude of the analog signal which is output from the potential difference output means with (ii) a magnitude of the analog signal which is output from the D/A conversion means being included in the A/D conversion means and re-converting the digital signal which is output from the A/D conversion means into an analog signal, and outputting a digital signal control signal for controlling the digital signal output from the A/D conversion means in such a way as to equalize the magnitudes of the analog signals; and (h1) an illuminance level updown counter for increasing or decreasing a value of the digital signal which is output therefrom, based on the digital signal control signal (i) which is output from the analog signal conversion means, and (h2) converting the digital signal into a digital signal which is output from the A/D conversion means; (i) the analog signal which is output from the D/A conversion means being a sum of the reference voltage and a voltage calculated by multiplying the thermal voltage by a variable. - View Dependent Claims (2, 4, 5)
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3. The illuminance sensor as defined in 2, wherein,
the variable is calculated in accordance with the following equation: -
B=2.3025×
log(Ev)where B is the variable and Ev is illuminance measured by the light receiving means. - View Dependent Claims (6)
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7. An illuminance sensor, comprising:
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light receiving means for outputting an electric signal corresponding to ambient brightness; A/D) conversion means for converting the electric signal output from the light receiving means into a digital signal; duty ratio determination means including;
an illuminance register storing the digital signal output from the A/D conversion means; and
duty ratio registers each storing a duty ratio which is output based on a value of the illuminance register, the duty ratio determination means determining the duty ratio of a PWM signal based on the digital signal output from the A/D conversion means;PWM signal output means for outputting the PWM signal based on the duty ratio output from the duty ratio determination means; temperature compensation means having same temperature characteristics as the light receiving means; light receiving signal logarithmic compression means for logarithmic-compressing the electric signal which is output from the light receiving means and outputting the electric signal as a voltage; temperature correction signal logarithmic compression means for logarithmic-compressing the electric signal which is output from the temperature compensation means and outputting the electric signal as a voltage; potential difference output means for outputting, as an analog signal, a difference between electric potentials output which are from the light receiving signal logarithmic compression means and the temperature correction signal logarithmic compression means, respectively; D/A conversion means being included in the A/D conversion means and re-converting the digital signal which is output from the A/D conversion means into an analog signal; and analog signal comparison means for comparing (i) a magnitude of the analog signal which is output from the potential difference output means with (ii) a magnitude of the analog signal which is output from the D/A conversion means, and outputting a digital signal control signal for controlling the digital signal output from the A/D conversion means in such a way as to equalize the magnitudes of the analog signals, the A/D conversion means increasing or decreasing a value of the digital signal which is output therefrom, based on the digital signal control signal. - View Dependent Claims (8, 9, 10, 11, 12)
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Specification