Output circuit for gray scale control, testing apparatus thereof, and method for testing output circuit for gray scale control

Abstract

An output circuit for gray scale control includes a low-side current mirror unit, a low-side gray scale control circuit, a high-side current mirror unit, a high-side gray scale control circuit, a current increment control circuit and a selective precharge control circuit. A gray scale control circuit for outputting gray scale signals is separated into the high side and the low side, thereby enabling the output-current characteristics to be controlled to be close to the γ characteristics of a light emitting device. In addition, variations in the current for each output unit can be suppressed by using multistage current mirrors.

1 - 7 . (canceled)  
   
   
       8 . An output circuit for gray scale control, comprising: 
 a power-supply voltage supply unit;    a first current supply unit;    a power-supply voltage supply wire connected to the power-supply voltage supply unit;    a first MISFET which is provided between the first current supply unit and the power-supply voltage supply unit and has a gate electrode connected to the power-supply voltage supply unit;    a plurality of gray scale control units each having a transistor connected to the power-supply voltage supply wire;    a second current supply unit;    a MISFET for tilted-bias which is connected to the second current supply unit and the power-supply voltage supply wire and is of the same conductive type as the first MISFET; and    a bias supply line which connects between a gate electrode of the first MISFET and a gate electrode of the MISFET for tilted-bias, is connected to the power-supply voltage supply wire, and controls currents flowing to the transistors.    
   
   
       9 . The output circuit for gray scale control of  claim 8 , wherein 
 the transistors are each a MISFET having a gate electrode connected to the bias supply line.    
   
   
       10 . The output circuit for gray scale control of  claim 8 , further comprising 
 a second MISFET which is connected to the power-supply voltage supply unit and constitutes a transmission-side current mirror together with the first MISFET, wherein    the second current supply unit is a reception-side current mirror which is connected to the transmission-side current mirror and is constituted of MISFETs of which conductive types are same as one another.    
   
   
       11 . The output circuit for gray scale control of  claim 8 , wherein 
 the plurality of gray scale control units are each a current adding-type D/A converter.    
   
   
       12 . The output circuit for gray scale control of  claim 8 , wherein 
 the plurality of gray scale control units has:    a plurality of current mirror units mutually parallel-connected to the power-supply voltage supply node to represent M gray scales when M is a multiple integer of 2;    the same number of selecting switches connected to the current mirror units; and    a current output unit connected to all the selecting switches, and    the current mirror unit is constituted of current mirrors constituted of the transistors.    
   
   
       13 . The output circuit for gray scale control of  claim 12 , wherein 
 the current mirror unit is constituted of 1, 2, . . . , M/2 pieces of current mirrors having mutually same device configurations to control the M gray scales.    
   
   
       14 . The output circuit for gray scale control of  claim 12 , wherein 
 the transistors are MISFETs having mutually same device configurations, and    an output current from each of the current mirror units is adjusted according to a ratio of a gate width of the MISFET to a gate length thereof.    
   
   
       15 . The output circuit for gray scale control of  claim 11 , wherein 
 the gray scale control unit has a plurality of gray scale generation units having the current mirror units and selecting switches having the same numbers of transfer gates and inverters connected to the current mirror units, and    the current mirror units and the selecting switches are collectively disposed for each gray scale generation unit.    
   
   
       16 . The output circuit for gray scale control of  claim 8 , wherein 
 the transistors are of the same conductive type and are a first transistor and a second transistor constituting a current mirror, and    the gray scale control unit has an output buffer unit having the first transistor, and a differential circuit having the second transistor.    
   
   
       17 . The output circuit for gray scale control of  claim 16 , wherein 
 a current flowing through the first transistor at the time of driving is larger than a current flowing through the second transistor.    
   
   
       18 . The output circuit for gray scale control of  claim 16 , wherein 
 the gray scale control unit further has a voltage selection switch for supplying a voltage for gray scale control to the output buffer unit.    
   
   
       19 . The output circuit for gray scale control of  claim 18 , wherein 
 the differential circuit has an operational amplifier of which an input unit is connected to the voltage selection switch and an output unit is connected to the output buffer unit.    
   
   
       20 . An output circuit for gray scale control, comprising: 
 a plurality of multistage current mirror units which are constituted of plurality of current mirrors, in which the same current as a current flowing through a first stage of the current mirrors flows to each of three or more stages of the current mirrors; and    a plurality of gray scale control units for receiving reference voltages and gray scale signals from each of the plurality of multistage current mirror units, and outputting gray scale controlling currents different from one another.    
   
   
       21 . The output circuit for gray scale control of  claim 20 , further comprising 
 an output control unit for receiving the gray scale controlling signals from the plurality of gray scale control units, and varying combinations of the gray scale controlling currents outputted according to the gray scale signals.    
   
   
       22 . The output circuit for gray scale control of  claim 20 , wherein 
 the plurality of gray scale control units are separated into low-side gray scale control units capable of controlling gray scales in the lowest range and high-side gray scale control units capable of controlling gray scales higher than those controlled by the low-side gray scale control units, among the plurality of gray scale control units, and    the plurality of multistage current mirror units are separated into low-side multistage current mirror units connected to the low-side gray scale control units and high-side multistage current mirror units connected to the high-side gray scale control units.    
   
   
       23 . The output circuit for gray scale control of  claim 22 , wherein 
 the output control unit controls such that only the gray scale controlling currents from the low-side gray scale control unit are outputted when the number of gray scales is equal to or less than a predetermined value, and the gray scale controlling currents from the high-side gray scale control unit are outputted in addition to the gray scale controlling currents from the low-side gray scale control unit when the number of gray scales exceeds the predetermined value.    
   
   
       24 . The output circuit for gray scale control of  claim 22 , wherein 
 the low-side multistage current mirror units, the high-side multistage current mirror units, the low-side gray scale control units and the high-side gray scale control units for at least three colors red, green and blue are integrated into a same chip.    
   
   
       25 . The output circuit for gray scale control of  claim 24 , wherein 
 the low-side multistage current mirror units and the high-side multistage current mirror units are each disposed in a pair to be adjacent to one another and are disposed in a predetermined order of colors in a column direction,    the low-side gray scale control units, the high-side gray scale control unit and the output control units are disposed substantially in a matrix, and    the low-side gray scale control unit, the high-side gray scale control unit and the output control unit which are connected to the one pair of the low-side multistage current mirror unit and the high-side multistage current mirror unit are collectively disposed.    
   
   
       26 . The output circuit for gray scale control of  claim 20 , wherein 
 each of the plurality of gray scale control units includes a plurality of gray scale generation units having current mirror units and selecting switches having the same numbers of transfer gates and inverters connected to the current mirror units, and    the current mirror units and the selecting switches are collectively disposed for each gray scale generation unit.    
   
   
       27 . The output circuit for gray scale control of  claim 22 , further comprising 
 a current increment control circuit for outputting to the output control unit currents for incrementing the output current from the low-side gray scale control unit and the output current from the high-side gray scale control unit upon reception of increment control signals and the reference voltage supplied from the multistage current mirrors.    
   
   
       28 . The output circuit for gray scale control of  claim 22 , further comprising 
 a current increment control circuit for outputting a current for incrementing the output current from the low-side gray scale control unit, between the low-side multistage current mirror unit and the low-side gray scale control unit.    
   
   
       29 . The output circuit for gray scale control of  claim 28 , wherein 
 the current increment control circuit has a function of increasing or reducing a current outputted in correspondence with a gray scale to be controlled.    
   
   
       30 . The output circuit for gray scale control of  claim 21 , wherein 
 the output control circuit further has:    a selective precharge circuit for supplying a voltage for charging an external signal line in accordance with switching control; and    a selective precharge control circuit for holding the selective precharge circuit in an on-state for a predetermined period of time in accordance with timing control corresponding to display data.    
   
   
       31 . An output circuit for gray scale control, comprising: 
 an internal circuit which is integrated into a semiconductor chip and has an output unit for outputting a current signal;    an external terminal provided on the semiconductor chip and connected to the output unit; and    a resistor which is provided on the semiconductor chip, is connected to the output unit, and converts the current signal into a voltage signal.    
   
   
       32 . The output circuit for gray scale control of  claim 31 , further comprising 
 a switching circuit connected to the resistor, wherein    the switching circuit is capable of performing switching operations so that:    at normal operation time and power cut time, the resistor and the internal circuit are mutually series connected to the external terminal; and    at testing time, the resistor is connected to the ground, and the resistor and the external terminal are mutually parallel connected to the output unit.    
   
   
       33 . The output circuit for gray scale control of  claim 31 , wherein 
 the internal circuit has:    a multistage current mirror unit; and    a gray scale control unit for outputting gray scale control current upon reception of a reference voltage from the multistage current mirror unit.    
   
   
       34 . An output circuit for gray scale control, comprising: 
 a plurality of gray scale control units having a plurality of bit cells;    a normal operating latch circuit provided for each bit cell;    a common latch circuit for supplying signals to all the bit cells; and    a selection circuit which is provided between the common latch circuit and the normal operating latch circuit and the bit cell and performs switching operations such that the signal from the normal operating latch circuit is transferred to the bit cell at normal operation time, and the signal outputted from the common latch circuit is transferred to the bit cell at testing time.    
   
   
       35 . The output circuit for gray scale control of  claim 34 , further comprising 
 a multistage current mirror unit for supplying reference voltages in each of the plurality of gray scale control units.    
   
   
       36 . A testing apparatus of an output circuit for gray scale control, comprising: 
 a substrate having an upper surface settable to a tester for testing wafers;    probes which are made of a conductor, are provided on an undersurface of the substrate, and receive current signals from at least from a wafer to be tested;    resistors disposed on the substrate in proximity to the probes and connected to the probes to convert the current signals into voltage signals; and    wires connected to the resistors and provided to pass through the substrate.    
   
   
       37 . The testing apparatus of an output circuit for gray scale control of  claim 36 , wherein 
 the distance between the probe and the resistor is equal to or less than 10 cm.    
   
   
       38 . The testing apparatus of an output circuit for gray scale control of  claim 36 , further comprising 
 operational amplifiers connected parallel to the resistors with respect to the probe, in which an output unit is connected to negative-side input units via the resistors.    
   
   
       39 . The testing apparatus of an output circuit for gray scale control of  claim 38 , wherein 
 a reference voltage outputted from the tester is inputted to a positive-side input unit of the operational amplifier.    
   
   
       40 . The testing apparatus of an output circuit for gray scale control of  claim 36 , wherein 
 the resistors are integrated.    
   
   
       41 . The testing apparatus of an output circuit for gray scale control, of  claim 38 , wherein 
 the operational amplifiers are integrated.    
   
   
       42 . A method for testing an output circuit for gray scale control comprising reference current sources connected to first resistors mutually parallel connected, and gray scale control units which are connected to the reference current sources and output currents for gray scale control, the method comprising: 
 connecting, at testing time, second resisters which are provided parallel to the first resisters and have a resistance value lower than that of the first resisters, to the reference current sources; and    turning off, at normal operation time, the connection between the second resisters and the reference current sources.