Reexamination Certificate
2000-03-27
2001-12-25
Cunningham, Terry D. (Department: 2816)
C327S538000, C327S543000, C326S082000, C326S083000, C345S100000
Reexamination Certificate
active
06332661
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a constant current driving apparatus which drives each of a lot of loads at a constant current, and a constant current driving semiconductor integrated circuit for use in such a constant current driving apparatus.
2. Description of the Related Art
Traditionally, in a light-emitting diode (abbreviated as “LED” hereinafter) printer head, an LED display panel which are formed by arranging a lot of LED devices, an organic electroluminescence (abbreviated as “EL” hereafter) display panel which utilizes an EL phenomenon of a specific organic compound, and the like, a lot of loads such as light-emitting devices are individually driven at a constant current. Since all these loads need to be driven at a time, they are often driven by using a plurality of constant current driver integrated circuits (occasionally abbreviated as “IC” hereinafter), which are semiconductor ICs provided with a plurality of constant current output terminals. In this case, when variations arise in output current values of the constant current driver ICs, variations arise in light-emitting amounts or the like of the light-emitting devices, print inconsistencies are caused in a printer, and display inconsistencies are caused in a display panel. In order to reduce such inconsistencies, it is required to minimize variations in output currents of the constant current driver ICs among the constant current output terminals.
On the other hand, in ICs produced from the same mask in the same process step and formed on different semiconductor chips, devices such as transistors and resistances formed on the semiconductor chips have different electrical characteristics, respectively, so that the ICs are not highly matched. However, among devices such as transistors and resistances formed on the same semiconductor chip, a relative error of electrical characteristics is small, so that the ICs are highly matched. For this reason, although variations in output currents of the driver ICs are small among constant current output terminals of the same IC, the variations are relatively large among different ICs. Therefore, in the case of using a plurality of driver ICs to drive light-emitting devices of an LED printer head, an LED display panel, an organic EL display panel and the like, it is required to correct variations among the driver ICs.
Variations among driver ICs are corrected by externally mounting a current setting resistance on each driver IC and regulating resistance values of the current setting resistances. Japanese Unexamined Patent Publication JP-A 8-169139 (1996) discloses a prior art of embedding a current setting resistance which is capable of changing a combined resistance value by combination in each driver IC used for driving an LED head, changing a combined resistance value of a combination of resistances so as to correspond to correction data from outside, and changing a constant current value.
In the conventional method of regulating a current setting resistance value and correcting variations among driver ICs used for driving at a constant current, there is a problem that it is hard to automate an assembly operation of assembling display devices and driver ICs in an LED printer head, an LED display panel, an organic EL display panel or the like. Although variations in constant current outputs are decreased by forming driver ICs into a single semiconductor integrated circuit, the size of the semiconductor integrated circuit is large and the area necessary for a semiconductor chip is also large. In addition, general versatility as a driver IC is lost, with the result that the driver IC becomes exclusive to a specific LED head, LED display panel, organic EL display panel or the like. Such a problem is also true in a driver IC which outputs a constant voltage.
SUMMARY OF THE INVENTION
An object of the invention is to provide a constant current driving apparatus and a constant current driving semiconductor integrated circuit, which can reduce inconsistencies of current in outputs among the plural parts of semiconductor circuits even in the case of driving a plurality of loads by a plurality of semiconductor circuits.
The invention provides a constant current driving apparatus which drives a plurality of loads at a same current,
the constant current driving apparatus comprising:
a plurality of constant current driving semiconductor integrated circuits, number of which is less than total number of the loads; and
a reference signal producing circuit for producing a reference signal,
each of the constant current driving semiconductor integrated circuits being formed of circuit elements integrated on a single semiconductor chip, and comprising:
a plurality of drive circuits having one or more reference input terminals, and two or more output terminals for driving two or more but part of the loads at a constant current corresponding to the reference signal inputted to the reference input terminal, and
a control circuit having driving input terminals for the loads for on-off-controlling outputs of the individual output terminals of the drive circuits in accordance with input signals to the driving input terminals,
the reference signal producing circuit being formed of circuit elements integrated on a single semiconductor chip, for supplying same reference signals, to the reference input terminals of the driver circuits in the plurality of constant current driving semiconductor integrated circuits.
According to the invention, a plurality of loads are driven individually at the same current by a plurality of drive circuits included in a plurality of constant current driving semiconductor integrated circuits. Each constant current driving semiconductor integrated circuit includes a drive circuit and a control circuit. The drive circuit has one or more reference input terminals and two or more output terminals and drives some of the loads individually at a constant current which is outputted to the respective output terminals, corresponding to reference signals inputted to the reference input terminals. The control circuit has driving input terminals for the individual loads and carries on-off control of outputs of the output terminals of the drive circuits individually in accordance with input signals to the driving input terminals. To the reference input terminal of the drive circuit, a reference signal from a reference signal producing circuit is supplied. The reference signal producing circuit is integrated on the same semiconductor chip as the constant current driving semiconductor integrated circuits, and produces a reference signal so as to supply the same reference signal to the reference input terminals of the constant current driving semiconductor integrated circuits. From the reference signal producing circuit, reference signals with small variations are produced and supplied to the individual reference input terminals of the drive circuit in the constant current driving semiconductor integrated circuits. Constant currents for driving the loads in correspondence with the reference signals in the individual constant current driving semiconductor integrated circuits are outputted from the drive circuits on the single semiconductor chip, so that variations can be minimized. Driving currents from different constant current driving semiconductor integrated circuits are also outputted in correspondence with reference signals with small variations produced from the reference signal producing circuit on the single semiconductor chip, so that variations in output currents can be minimized without regulation by a resistance or the like.
As described above, according to the invention, it is possible to drive a plurality of loads at constant currents with small variations supplied from a plurality of constant current driving semiconductor integrated circuits, and on-off-control driving outputs. Since regulation among the constant current driving semiconductor integrated circuits is not necessary in order to minimize variations in outpu
Cunningham Terry D.
Nguyen Long
Sharp Kabushiki Kaisha
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