Light emitting diode driving device and optical transmission device including the same
A light emitting diode driving device for driving an LED includes (i) a driving pulse current generating circuit for generating a driving current for the LED in accordance with a driving pulse signal supplied from outside and (ii) a differentiating circuit for generating a peaking current obtained by differentiating the driving pulse signal. A current that is equal to the sum of the driving current and the peaking current flows to the LED. The light emitting diode driving device further includes a peaking control circuit for controlling the magnitude of the peaking current generated from the differentiating circuit.
1. A light emitting diode driving circuit for driving a light emitting diode, comprising:
a driving current generating circuit generating a driving current for the light emitting diode in accordance with a driving pulse signal supplied from outside;
a peaking current generating circuit generating a peaking current obtained by differentiating the driving pulse signal; and
a peaking current control circuit controlling a magnitude of the peaking current generated from the peaking current generating circuit,
a current that is equal to a sum of the driving current and the peaking current flowing to the light emitting diode, wherein:
the driving current generating circuit includes:
a constant current circuit; and
a switching circuit provided between the constant current circuit and the light emitting diode, for carrying out ON-OFF control of the light emitting diode in accordance with the driving pulse signal, and
the peaking current generating circuit includes a first differentiating circuit, wherein the first differentiating circuit comprises:
a first resistor whose one end is connected with a cathode of the light emitting diode;
a first capacitor whose one end is connected with another end of the first resistor;
an inverter circuit to which the driving pulse signal is inputted; and
a MOS transistor whose drain is connected with another end of the first capacitor, source is connected with an output terminal of the inverter circuit, and gate receives a control voltage for controlling the peaking current.
2. The light emitting diode driving circuit as set forth in claim 1 , wherein the peaking current control circuit controls the magnitude of the peaking current in accordance with a temperature change in the peaking current.
3. The light emitting diode driving circuit as set forth in claim 1 , wherein the peaking current control circuit controls the magnitude of the peaking current in accordance with a temperature change in the driving current.
4. The light emitting diode driving circuit as set forth in claim 1 , wherein the control voltage applied to the gate of the MOS transistor is a voltage obtained by level shifting a peaking control voltage by a threshold voltage.
5. The light emitting diode driving circuit as set forth in claim 4 , wherein the peaking control voltage has a temperature characteristic of a fixed value.
6. The light emitting diode driving circuit as set forth in claim 1 , wherein
a second differentiating circuit is connected in parallel with the MOS transistor, the first capacitor and the first resistor of the first differentiating circuit; and
the second differentiating circuit includes:
a second capacitor connected with an output terminal of the inverter circuit; and
a second resistor whose one end is connected with the cathode of the light emitting diode and another end is connected with the second capacitor.
7. The light emitting diode driving circuit as set forth in claim 6 , wherein:
the inverter circuit includes a first inverter circuit provided for the first differentiating circuit and a second inverter circuit provided for the second differentiating circuit; and
a phase adjusting circuit is provided before the first inverter circuit of the first differentiating circuit and the second inverter circuit of the second differentiating circuit, for matching a phase of the peaking current outputted from the first differentiating circuit with a phase of the peaking current outputted from the second differentiating circuit.
8. The light emitting diode driving circuit as set forth in claim 1 , further comprising a bias current output circuit outputting a constant bias current as a driving current when the light emitting diode is OFF.
9. An optical transmission device comprising a light emitting diode driving circuit,
the light emitting diode driving circuit including:
a driving current generating circuit generating a driving current for a light emitting diode in accordance with a driving pulse signal supplied from outside;
a peaking current generating circuit generating a peaking current obtained by differentiating the driving pulse signal, and
a peaking current control circuit controlling a magnitude of the peaking current generated from the peaking current generating circuit,
a current that is equal to a sum of the driving current and the peaking current flowing to the light emitting diode, and
the light emitting diode driving circuit being applicable to a driving circuit of a semiconductor light emitting element for an optical fiber communication, for a space light transmission communication or for a photocoupler signal transmission, wherein
the driving current generating circuit of the light emitting diode driving circuit includes:
a constant current circuit; and
a switching circuit provided between the constant current circuit and the light emitting diode, for carrying out ON-OFF control of the light emitting diode in accordance with the driving pulse signal, and
the peaking current generating circuit of the light emitting diode driving circuit includes a first differentiating circuit, wherein the first differentiating circuit comprises:
a first resistor whose one end is connected with a cathode of the light emitting diode;
a first capacitor whose one end is connected with another end of the first resistor;
an inverter circuit to which the driving pulse signal is inputted; and
a MOS transistor whose drain is connected with another end of the first capacitor, source is connected with an output terminal of the inverter circuit, and gate receives a control voltage for controlling the peaking current.
10. The optical transmission device as set forth in claim 9 , wherein the peaking current control circuit of the light emitting diode driving circuit controls a magnitude of the peaking current in accordance with a temperature change in the peaking current.
11. The optical transmission device as set forth in claim 9 , wherein the peaking current control circuit of the light emitting diode driving circuit controls a magnitude of the peaking current in accordance with a temperature change in the driving current.
12. The optical transmission device as set forth in claim 9 , wherein the light emitting diode driving circuit includes a bias current output circuit outputting a constant bias current as a driving current when the light emitting diode is OFF.