Analog to digital encoder

Claim 2

A photoresponsive device adapted for use in an analog to digital encoder comprising, in combination: a light source, a silicon photovoltaic photodiode having a first terminal and a second terminal and adapted to generate a voltaic potential between said terminals responsive to light from the source, one of said terminals being positive and the other negative in polarity, a mechanically actuatable light shutter disposed between the light source and the silicon photodiode, a transistor having a base, a collector and an emitter, the emitter and collector being of semi-conductor material doped with impurities of a first type and the base being of semi-conductor material doped with impurities of a second type, the base of said transistor being electrically connected to the second terminal of the photodiode, said transistor being electrically connected in a common emitter switching circuit having a direct current power source in series with the emitter and collector of the transistor, a direct current bias source connected in a series circuit between said first terminal of said photodiode and said emitter of said transistor, said transistor having a characteristic such that a minimum threshold potential of one polarity is required between said base and said emitter to produce conduction between said emitter and said collector, said photovoltaic photodiode and said bias source being additively polarized whereby the sum of their output voltages appears between said base and said emitter and tends to cause conduction between said emitter and said collector of said transistor, said bias source having an output voltage less than said threshold potential and thus insufficient by itself to cause conduction between said emitter and said collector of said transistor, said photovoltaic photodiode when illuminated by said light source having a photovoltaic output voltage which is sufficient when added to said output voltage of said bias source to equal or exceed said threshold potential and thereby to cause conduction between said emitter and said collector of said transistor, and a load electrically connected in the series emitter-collector circuit of the transistor whereby illumination of the silicon photodiode causes the transistor to conduct and to develop a potential across the load.

Claim 3

A photoresponsive device comprising the combination of claim 1 in combination with a dirEct current amplifier coupled to the load, said direct current amplifier comprising a second transistor connected in a common emitter amplifier circuit, said second transistor having a base of semi-conductor material doped with impurities of the first type and a collector and an emitter of semi-conductive material doped with impurities of the second type, the load being electrically connected in a series circuit with base and emitter of the second transistor, and the collector and emitter of the second transistor being electrically connected in a series electrical circuit with a second load and the direct current power source, whereby the electrical output of the device appears across the second load.

Claim 4

A photoresponsive device comprising the combination of claim 1 wherein said bias source includes means for changing the potential of the bias source with temperature in approximately the same manner as the base-to-emitter threshold potential of the transistor changes with temperature.

Claim 5

A photoresponsive device comprising the combination of claim 1 wherein the direct current bias source comprises an additional transistor of the same type as the first-mentioned transistor and of similar characteristics, said additional transistor having a base electrically connected to the first terminal of the photodiode, said additional transistor having a collector and an emitter connected in a series circuit with the power source and a transistor, said emitter of said additional transistor being connected to said emitter of said first-mentioned transistor, and means for causing conduction in said additional transistor, whereby the potential difference between the base and emitter of said additional transistor is utilized as the bias potential, the variation of said potential difference with temperature changes being approximately the same as the variation of said threshold voltage of said first-mentioned transistor.

Claim 6

A photoresponsive device comprising the combination of claim 4 wherein the first-mentioned and additional transistors are silicon transistors.

Claim 7

A position responsive analog to digital encoder comprising, in combination: a code member adapted to be moved responsive to positional changes to be encoded and having a plurality of tracks of transparent sectors separated by opaque sectors, each track moving responsive to positional changes normal to a read-out line disposed in a fixed position relative to the code member, a light source confronting one side of the code member and illuminating each track of the code member at the read-out line, a plurality of photovoltaic photodiodes having a first terminal and a second terminal, each track of the code member being confronted by a photodiode at the read-out line thereof to receive illumination from the track, a plurality of switching transistors, each switching transistor having a base of semi-conductor material doped with impurities of a first type and a collector and emitter of semi-conductor material doped with impurities of a second type, the second terminal of each photodiode being connected to the base of a different switching transistor, each of said switching transistors being connected in a separate common emitter switching circuit and having a collector-emitter circuit including a direct current power source and a resistor, a direct current bias source connected in common between said first terminal of each diode and said emitter of each transistor, each transistor having a characteristic such that a minimum threshold potential of one polarity is required between said base and said emitter thereof to produce conduction between said emitter and said collector thereof, each photodiode and said bias source being additively polarized whereby the sum of their output voltages appears between the base and the emitter of the corresponding transistor and tends to cause conduction between said emitter and said collector thereof, said bias source having an output voltage less than said threshold potential and thus insufficient by itself tO cause conduction in said transistors, each photodiode when illuminated by said light source having a photovoltaic output voltage which is sufficient when added to said output voltage of said bias source to equal or exceed said threshold potential and thereby to cause conduction between said emitter and said collector of the corresponding transistor, and a load electrically connected in the series emitter-collector circuit of each switching transistor.

Claim 8

A position responsive analog to digital encoder comprising, in combination: a code member adapted to be moved responsive to positional changes to be encoded and having a plurality of tracks of transparent sectors separated by opaque sectors, each track moving responsive to positional changes normal to a read-out line disposed in a fixed position relative to the code member, a light source confronting one side of the code member and illuminating each track of the code member at the read-out line, a plurality of photovoltaic photodiodes having a first terminal and a second terminal, each track of the code member being confronted by a photodiode at the read-out line thereof to receive illumination from the track, a plurality of switching transistors, each switching transistor having a base of semi-conductor material doped with impurities of a first type and a collector and emitter of semi-conductor material doped with impurities of a second type, the second terminal of each photodiode being connected to the base of a different switching transistor, each of said switching transistors being connected in a separate common emitter switching circuit and having a collector-emitter circuit including a direct current power source and a resistor, a direct current bias source connected in common between said first terminal of each diode and said emitter of each transistor, each transistor having a characteristic such that a minimum threshold potential of one polarity is required between said base and said emitter thereof to produce conduction between said emitter and said collector thereof, each photodiode and said bias source being additively polarized whereby the sum of their output voltages appears between the base and the emitter of the corresponding transistor and tends to cause conduction between said emitter and said collector thereof, said bias source having an output voltage less than said threshold potential and thus insufficient by itself tO cause conduction in said transistors, each photodiode when illuminated by said light source having a photovoltaic output voltage which is sufficient when added to said output voltage of said bias source to equal or exceed said threshold potential and thereby to cause conduction between said emitter and said collector of the corresponding transistor, and a load electrically connected in the series emitter-collector circuit of each switching transistor.

Claim 9

A position responsive analog to digital encoder comprising the combination of claim 6 wherein said bias source includes means for changing the potential of the bias source with ambient temperature in approximately the same manner as the base-to-emitter threshold potentials of the switching transistors change with ambient temperature.

Claim 10

A position responsive analog to digital encoder comprising the combination of claim 6 wherein the direct current bias source comprises a bias transistor of the same type as the switching transistors and of similar characteristics, said bias transistor having a base electrically connected to the first terminal of each photodiode, said bias transistor having an emitter and a collector connected in a series circuit with the power source and a resistor, said emitter of said bias transistor being connected to said emitters of said switching transistors, and means for causing conduction in said bias transistor, whereby the voltage difference between the base and emitter of said bias transistor is utilized as the bias potential, the variation of said voltage difference with temperature changes being approximately the same as the variation of said threshold voltage of said switching transistors.

Claim 11

A position responsive analog to digital encoder comprising the combination of claim 8 in which said last-mentioned means includes a second resistor connected between the base of the bias transistor and the terminal of the power source connected to the collector of the bias transistor.

Claim 12

A position responsive analog to digital encoder comprising the combination of claim 6 in combination with a plurality of potential responsive electronic switches electrically connected in the corresponding emitter-to-power source circuits of the respective switching transistors.

Claim 13

A position responsive analog to digital encoder comprising the combination of claim 10 wherein each electronic switch comprises a transistor having a collector connected to the emitter of the associated switching transistor and an emitter electrically connected to the power source, each electronic switch transistor being rendered conductive in response to a potential impressed on the base thereof.

Claim 14

A position responsive analog to digital encoder comprising the combination of claim 11 wherein the bases of all electronic switch transistors are interconnected and connected to one terminal of a periodic pulse generator, the other terminal of the pulse generator being electrically connected to the power source.

Claim 15

A position responsive analog to digital encoder comprising the combination of claim 11 in combination with a sequential pulse generator having a plurality of output terminals, said sequential pulse generator producing a series of pulses at time intervals on different output terminals thereof, the base of each electronic switch transistor being connected to a different output terminal.

Claim 16

A position responsive analog to digital encoder comprising the combination of claim 6 in combination with a plurality of direct current amplifiers, each amplifier being coupled to the load of a different switching transistor and having a transistor with a base of semi-conductor material doped with impurities of the first type and an emitter and a collector doped with impurities of the second type, each amplifier being connected in a common emitter amplifier circuit.