Method and apparatus for generating ratiometric control signals
First Claim
1. A circuit comprising:
- a single voltage source;
a first photodiode having an anode and a cathode, the cathode being coupled to said single voltage source;
a second photodiode having an anode, and a cathode, the cathode of the second photodiode being coupled to the anode of the first photodiode, the anode of the second photodiode being coupled to the single voltage source; and
a ratiometric sensor output line coupled to a junction between the anode of the first photodiode and the cathode of the second photodiode;
wherein a variation in power supplied by the single voltage source affects the first photodiode and the second photodiode substantially equally.
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Abstract
A ratiometric sensor is formed of a first photodiode connected in series with an electronic component, such as a second photodiode or a resistor, between a source of first voltage and a source of second voltage. The ratiometric sensor supplies a "ratiometric voltage" on a ratiometric sensor output line that is connected to a junction between the first photodiode and the electronic component. The ratiometric voltage is proportional to the ratio of the equivalent resistance of the first photodiode to the sum of the equivalent resistances of the first photodiode and the electronic component. A ratiometric sensor that uses a photodiode and a resistance has a large dynamic range because the ratiometric voltage can vary between the first voltage and the second voltage. A ratiometric sensor that uses two photodiodes is less sensitive to noise than a conventional circuit that uses a single photodiode, because noise can get canceled from the numerator and denominator of the ratio. The ratiometric signal can be digitized by an analog-to-digital converter that can include, for example, a 555 timer, a Darlington transistor or a combination of a resistor and a capacitor.
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Citations
29 Claims
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1. A circuit comprising:
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a single voltage source; a first photodiode having an anode and a cathode, the cathode being coupled to said single voltage source; a second photodiode having an anode, and a cathode, the cathode of the second photodiode being coupled to the anode of the first photodiode, the anode of the second photodiode being coupled to the single voltage source; and a ratiometric sensor output line coupled to a junction between the anode of the first photodiode and the cathode of the second photodiode; wherein a variation in power supplied by the single voltage source affects the first photodiode and the second photodiode substantially equally. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A method comprising:
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coupling a cathode of a first photodiode to a positive terminal of a single voltage source; coupling an anode of the first photodiode to a cathode of a second photodiode; coupling an anode of the second photodiode to a negative terminal of the single voltage source; and coupling a ratiometric sensor output line to a junction between the anode of the first photodiode and the cathode of the second photodiode. - View Dependent Claims (24)
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25. A circuit comprising:
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a first signal sensor having a first sensor terminal and a second sensor terminal, the first signal sensor being capable of sensing the intensity of a signal incident on the first signal sensor; a second signal sensor having a third sensor terminal and a fourth sensor terminal, the third sensor terminal being coupled to the second sensor terminal, the second signal sensor being capable of sensing the intensity of the signal incident on the second signal sensor; and a single voltage source coupled to the first sensor terminal and the fourth sensor terminal, wherein a variation in power supplied by the single voltage source affects operation of the first signal sensor and the second signal sensor substantially equally. - View Dependent Claims (26, 27, 28, 29)
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Specification