Drive circuit of light emitting element
First Claim
1. A drive circuit of a light emitting element comprising:
- a differential output circuit which comprises first and second transistors each having a control terminal and first and second terminals, and the first terminals connected to each other and a current/voltage conversion element connected between a connection point of the first terminals of the first and second transistors and a reference potential, and the second terminal of the second transistor is connected to a power supply voltage source;
an input circuit which receives differential drive signals and supplies differential signals in accordance with levels of supplied drive voltages to the control terminals of the first and second transistors of the differential output circuit;
a reference voltage generation circuit which generates a reference voltage;
a comparison circuit which compares the potential of the connection point of the first terminals of the first and second transistors of the differential output circuit with the reference voltage and outputs a signal of a level in accordance with the result of comparison; and
a variable voltage supply circuit which generates a voltage in accordance with the level of the output signal of the comparison circuit and supplies the same as the supplied drive voltage to the input circuit.
1 Assignment
0 Petitions
Accused Products
Abstract
A drive circuit of a light emitting element capable of setting a desired constant current and capable of operating stably at a high speed while holding a forward direction voltage required for the emission of light even under a low power supply voltage, wherein there is provided an input circuit which receives differential drive signals and outputs differential signals of levels in accordance with the level of a supplied drive voltage, a differential output circuit in which an emitter-connection portion of transistors is grounded via a resistor, the differential signals and are supplied to bases, and a laser diode is connected to a collector of the transistor, a reference voltage generation circuit which generates a reference voltage, a comparison circuit which compares the voltage of the emitter-connection portion with the reference voltage and outputs a signal of the level in accordance with the result of comparison, and a variable voltage supply circuit which generates a voltage in accordance with the input level of the output signal and supplies the same as the drive voltage of the input circuit.
-
Citations
44 Claims
-
1. A drive circuit of a light emitting element comprising:
-
a differential output circuit which comprises first and second transistors each having a control terminal and first and second terminals, and the first terminals connected to each other and a current/voltage conversion element connected between a connection point of the first terminals of the first and second transistors and a reference potential, and the second terminal of the second transistor is connected to a power supply voltage source; an input circuit which receives differential drive signals and supplies differential signals in accordance with levels of supplied drive voltages to the control terminals of the first and second transistors of the differential output circuit; a reference voltage generation circuit which generates a reference voltage; a comparison circuit which compares the potential of the connection point of the first terminals of the first and second transistors of the differential output circuit with the reference voltage and outputs a signal of a level in accordance with the result of comparison; and a variable voltage supply circuit which generates a voltage in accordance with the level of the output signal of the comparison circuit and supplies the same as the supplied drive voltage to the input circuit. - View Dependent Claims (2, 3, 4, 5)
-
-
6. A drive circuit of a light emitting element, comprising:
-
a differential output circuit which comprises first and second transistors each having a control terminal and first and second terminals, and the first terminals connected to each other and a current/voltage conversion element connected between a connection point of the first terminals of the first and second transistors and a reference potential, and the second terminal of the second transistor is connected to a power supply voltage source; an input circuit which receives differential drive signals and supplies differential signals in accordance with levels of supplied drive voltages to the control terminals of the first and second transistors of the differential output circuit; a reference voltage generation circuit which generates a reference voltage; a dummy circuit for generating a comparison voltage having substantially the same value as the potential of the connection point of the first terminals of the first and second transistors of the differential output circuit upon receipt of the supplied drive voltage; a comparison circuit which compares the comparison voltage generated by the dummy circuit with the reference voltage and outputs a signal of a level in accordance with the result of comparison; and a variable voltage supply circuit which generates a voltage in accordance with the level of the output signal of the comparison circuit and supplies the same as the supplied drive voltage to the input circuit and the dummy circuit. - View Dependent Claims (7, 8, 9, 10, 11)
-
-
12. A drive circuit of a light emitting element comprising:
-
a differential output circuit which comprises first and second transistors each having a control terminal and first and second terminals, and can adjust the amounts of current flowing between the first and second terminals in accordance with the level of a signal supplied to the control terminals, and the first terminals connected to each other and which comprises a current/voltage conversion element connected between a connection point of the first terminals of the first and second transistors and a reference potential, and the second terminal of the second transistor is connected to a power supply voltage source; an input-circuit which receives differential drive signals and supplies differential signals in accordance with levels of supplied drive voltages to the control terminals of the first and second transistors of the differential output circuit; a reference voltage generation circuit which generates a reference voltage; a comparison circuit which compares the potential of the connection point of the first terminals of the first and second transistors of the differential output circuit with the reference voltage and outputs a signal of a level in accordance with the result of comparison; and a variable voltage supply circuit which generates a voltage in accordance with the input level of the output signal of the comparison circuit and supplies the same as the supplied drive voltage to the input circuit. - View Dependent Claims (13, 14, 15, 16)
-
-
17. A drive circuit of a light emitting element, comprising:
-
a differential output circuit which comprises first and second transistors each having a control terminal and first and second terminals, and can adjust the amounts of current flowing between the first and second terminals in accordance with the level of a signal supplied to the control terminals, and the first terminals connected to each other and which comprises a current/voltage conversion element connected between a connection point of the first terminals of the first and second transistors and a reference potential, and the second terminal of the second transistor is connected to a power supply voltage source; an input circuit which receives differential drive signals and supplies differential signals in accordance with levels of supplied drive voltages to the control terminals of the first and second transistors of the differential output circuit; a reference voltage generation circuit which generates a reference voltage; a dummy circuit for generating a comparison voltage having substantially the same value as the potential of the connection point of the first terminals of the first and second transistors of the differential output circuit upon receipt of the supplied drive voltage; a comparison circuit which compares the comparison voltage generated by the dummy circuit with the reference voltage and outputs a signal of a level in accordance with the result of comparison; and a variable voltage-supply circuit which generates a voltage in accordance with the level of the output signal of the comparison circuit and supplies the same as the supplied drive voltage to the input circuit and the dummy circuit. - View Dependent Claims (18, 19, 20, 21, 22)
-
-
23. A light emitting apparatus, comprising:
-
a differential output circuit which comprises first and second transistors each having a control terminal and first and second terminals, and the first terminals connected to each other and a current/voltage conversion element connected between a connection point of the first terminals of the first and second transistors and a reference potential, and the second terminal of the second transistor is connected to a power supply voltage source; a light emitting element connected between the second terminal of the first transistor and the power supply voltage source; an input circuit which receives differential drive signals and supplies differential signals in accordance with levels of supplied drive voltages to the control terminals of the first and second transistors of the differential output circuit; a reference voltage generation circuit which generates a reference voltage; a comparison circuit which compares the potential of the connection point of the first terminals of the first and second transistors of the differential output circuit with the reference voltage and outputs a signal of a level in accordance with the result of comparison; and a variable voltage supply circuit which generates a voltage in accordance with the level of the output signal of the comparison circuit and supplies the same as the supplied drive voltage to the input circuit. - View Dependent Claims (24, 25, 26, 27)
-
-
28. A light emitting apparatus, comprising:
-
a differential output circuit which comprises first and second transistors each having a control terminal and first and second terminals, and the first terminals connected to each other and a current/voltage conversion element connected between a connection point of the first terminals of the first and second transistors and a reference potential, and the second terminal of the second transistor is connected to a power supply voltage source; a light emitting element connected between the second terminal of the first transistor and the power supply voltage source, an input circuit which receives differential drive signals and supplies differential signals in accordance with levels of supplied drive voltages to the control terminals of the first and second transistors of the differential output circuit; a reference voltage generation circuit which generates a reference voltage; a dummy circuit for generating a comparison voltage having substantially the same value as the potential of the connection point of the first terminals of the first and second transistors of the differential output circuit upon receipt of the supplied drive voltage; a comparison circuit which compares the comparison voltage generated by the dummy circuit with the reference voltage and outputs a signal of a level in accordance with the result of comparison; and a variable voltage supply circuit which generates a voltage in accordance with the level of the output signal of the comparison circuit and supplies the same as the supplied drive voltage to the input circuit and the dummy circuit. - View Dependent Claims (29, 30, 31, 32, 33)
-
-
34. A light emitting apparatus comprising:
-
a differential output circuit which comprising first and second transistor each having a control terminal and first and second terminals, and can adjust the amounts of current flowing between the first and second terminals in accordance with the level of a signal supplied to the control terminals, and the first terminals connected to each other and which comprises a current/voltage conversion element connected between a connection point of the first terminals of the first and second transistors and a reference potential, and the second current input/output terminal of the second transistor is connected to a power supply voltage source; a light emitting element connected between the second terminal of the first transistor and the power supply voltage source; an input circuit which receives differential drive signals and supplies differential signals in accordance with levels of supplied drive voltages to the control terminals of the first and second transistors of the differential output circuit; a reference voltage generation circuit which generates a reference voltage; a comparison circuit which compares the potential of the connection point of the first terminals of the first and second transistors of the differential output circuit with the reference voltage and outputs a signal of a level in accordance with the result of comparison; and a variable voltage supply circuit which generates a voltage in accordance with the input level of the output signal of the comparison circuit and supplies the same as the supplied drive voltage to the input circuit. - View Dependent Claims (35, 36, 37, 38)
-
-
39. A light emitting apparatus, comprising:
-
a differential output circuit which comprises first and second transistors each having a control terminal and first and second terminals, and can adjust the amounts of current flowing between the first and second terminals in accordance with the level of a signal supplied to the control terminals, and the first terminals connected to each other and which comprises a current/voltage conversion element connected between a connection point of the first terminals of the first and second transistors and a reference potential, and the second terminal of the second transistor is connected to a power supply voltage source; a light emitting element connected between the second terminal of the first transistor and the power supply voltage; an input circuit which receives differential drive signals and supplies differential signals in accordance with levels of supplied drive voltages to the control terminals of the first and second transistors of the differential output circuit; a reference voltage generation circuit which generates a reference voltage; a dummy circuit for generating a comparison voltage having substantially the same value as the potential of the connection point of the first terminals of the first and second transistors of the differential output circuit upon receipt of the supplied drive voltage; a comparison circuit which compares the comparison voltage generated by the dummy circuit with the reference voltage and outputs a signal of a level in accordance with the result of comparison; and a variable voltage supply circuit which generates a voltage in accordance with the level of the output signal of the comparison circuit and supplies the same as the supplied drive voltage to the input circuit and the dummy circuit. - View Dependent Claims (40, 41, 42, 43, 44)
-
Specification