Laser driver with maintaining average optical power constant
First Claim
1. A laser driver for generating a driving current for a semiconductor laser element in response to a differential input signal, the semiconductor laser element receiving a direct current from a direct current source connected in series with the semiconductor laser element, the laser driver comprising:
- a differential amplifier including;
an upper node,a lower node connected to a reference potential line,a first current source to provide a first source current flowing in the lower node;
a pair of first resistors each having a first end and second end, the first ends of the first resistors being connected with the upper node, the second end of one of the first resistors outputting a driving signal, the second end of another of the first resistors outputting a reverse driving signal having a phase opposite to a phase of the driving signal, anda pair of first transistors configured to divide the first source current into a first current and a second current in response to the differential input signal, the first current flowing in the second end of the one of the first resistors, the second current flowing in the second end of the another of the first resistors,a target potential circuit configured to generate a target potential;
an adjusting circuit including a variable resistor connected between a power supply line and the upper node of the differential amplifier, the adjusting circuit being configured to adjust resistance of the variable resistor so as to reduce a difference between the target potential and a center potential between the driving signal and the reverse driving signal; and
a bypass circuit connected in parallel with the semiconductor laser element, the bypass circuit being configured to output an output current in response to the driving signal;
wherein the driving current is generated by subtracting the output current from the direct current.
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Accused Products
Abstract
The laser driver including a difference amplifier, a target potential circuit, an adjusting circuit, and bypass circuit is disclosed. The differential amplifier outputs a driving signal and a reverse driving signal having a phase opposite to a phase of the driving signal. The bypass circuit outputs an output current in response to the driving signal for generating a driving current for a semiconductor laser element that emits an optical signal in response to the driving signal. The adjusting circuit controls average potential of the driving signal and the reverse driving signal, so that the average potential becomes substantially equal to a target potential provided by the target potential circuit. The target potential corresponds to average optical power of the optical signal. When amplitude of the driving signal is changed for adjusting an extinction ratio of the optical signal, the adjusting circuit maintains the average optical power in a constant value.
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Citations
6 Claims
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1. A laser driver for generating a driving current for a semiconductor laser element in response to a differential input signal, the semiconductor laser element receiving a direct current from a direct current source connected in series with the semiconductor laser element, the laser driver comprising:
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a differential amplifier including; an upper node, a lower node connected to a reference potential line, a first current source to provide a first source current flowing in the lower node; a pair of first resistors each having a first end and second end, the first ends of the first resistors being connected with the upper node, the second end of one of the first resistors outputting a driving signal, the second end of another of the first resistors outputting a reverse driving signal having a phase opposite to a phase of the driving signal, and a pair of first transistors configured to divide the first source current into a first current and a second current in response to the differential input signal, the first current flowing in the second end of the one of the first resistors, the second current flowing in the second end of the another of the first resistors, a target potential circuit configured to generate a target potential; an adjusting circuit including a variable resistor connected between a power supply line and the upper node of the differential amplifier, the adjusting circuit being configured to adjust resistance of the variable resistor so as to reduce a difference between the target potential and a center potential between the driving signal and the reverse driving signal; and a bypass circuit connected in parallel with the semiconductor laser element, the bypass circuit being configured to output an output current in response to the driving signal; wherein the driving current is generated by subtracting the output current from the direct current. - View Dependent Claims (2, 3, 4, 5, 6)
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Specification