Driver circuit, optical print head, and image forming apparatus
A driver circuit in an optical print head uses driving transistors to drive a row of light-emitting elements. The gate electrodes of the driving transistors are at least partly oriented so that driving current flows in the channels below the gate electrodes in a direction different from the direction of the row the light-emitting elements. This orientation reduces the temperature dependency of the driving current, so that the optical print head can produce the same high image quality at low ambient temperatures as at room temperature.
1. A driver circuit having a plurality of driving transistors for supplying driving current to a plurality of driven elements, the driven elements being disposed in a row oriented in a first direction,
wherein the driving transistors have respective gate electrodes with respective first parts and conduct the driving current below the first parts of the gate electrodes in a second direction differing from the first direction,
wherein the second direction is substantially orthogonal to the first direction, and
wherein the gate electrodes also have respective second parts and the driving transistors conduct the driving current below the second parts of the gate electrodes in a third direction differing from the second direction.
2. The driver circuit of claim 1 , wherein the driving transistors are metal-oxide-semiconductor transistors with respective source areas and drain areas located on opposite sides of the first parts of the gate electrodes as seen in the second direction.
3. The driver circuit of claim 1 , wherein the driving current flows only in the second direction below the gate electrodes of the driving transistors.
4. The driver circuit of claim 1 , wherein the third direction is substantially orthogonal to the second direction.
5. The driver circuit of claim 1 , wherein the first and second parts of each one of the gate electrodes form a unitary L-shaped structure.
6. The driver circuit of claim 5 , wherein each one of the gate electrodes also includes at least one third part disposed parallel to the first part in a rectangular area bounded on two sides by the unitary L-shaped structure.
7. The driver circuit of claim 1 , wherein the first and second parts of each one of the gate electrodes form a unitary U-shaped structure.
8. The driver circuit of claim 7 , wherein each one of the gate electrodes also includes at least one third part disposed parallel to the first part in a rectangular area bounded on three sides by the unitary U-shaped structure.
9. The driver circuit of claim 1 , wherein the first and second parts of each one of the gate electrodes form a unitary structure bounding a closed area.
10. The driver circuit of claim 1 , wherein the first and second parts of each one of the gate electrodes form a unitary structure bounding a plurality of closed areas.
11. The driver circuit of claim 10 , wherein the first and second parts of each one of the gate electrodes form an orthogonal grid.
12. The driver circuit of claim 1 , wherein the driving transistors include both main driving transistors having gate electrodes with both the first and the second parts and auxiliary driving transistors having gate electrodes with only the first parts.
13. The driver circuit of claim 1 , wherein the driving current flows only in the second direction below the gate electrodes of the driving transistors.
14. An optical print head comprising:
the driver circuit of claim 1 ;
a substrate on which the driver circuit is mounted;
an array of light-emitting elements functioning as the driven elements driven by the driver circuit; and
an array of lenses for focusing light emitted from the array of light-emitting elements.
15. An image forming apparatus comprising:
the optical print head of claim 14 ; and
a photosensitive member for receiving the light focused by the array of lenses in the optical print head.