Pixel driving device, light emitting device, and property parameter acquisition method in a pixel driving device

A light emitting device, comprising:

• a pixel array, which is constituted with a plurality of pixels arranged, connected to each of a plurality of signal lines, and each comprising a light emitting element, and a pixel drive circuit having a drive transistor for controlling the current supplied to the light emitting element with one end of the current path of the drive transistor connected to one terminal of the light emitting element as well as a holding capacity for storing charge by voltage impressed on a current control terminal of the drive transistor;
• a voltage impressing circuit for outputting a reference voltage;
• a plurality of voltage measurement circuits equipped respectively for connecting to each of the plurality of signal lines;
• a switching circuit for switching connection of one end of each signal line, between the voltage impressing circuit and each voltage measurement circuit;
• and
• a property parameter acquisition circuit for acquiring the property parameters that relate to the electrical properties of each pixel;
• wherein,
• the reference voltage has an electric potential in which the electric potential difference of the one end with respect to the other end of the current path of the drive transistor is a value that exceeds a threshold voltage of the drive transistor;
• and
• the switching circuit connects the one end of each signal line to the voltage impressing circuit sets the connection between the one end of each signal line and the voltage impressing circuit being interrupted after impressing the reference voltage for a predetermined time on the one end of each signal line by the voltage impressing circuit, and connects one end of each signal line to each voltage measurement circuit subsequent to a predetermined settling time elapsing;
• and
• each voltage measurement circuit acquires the voltage of the one end of each signal line as the measured voltage when being connected with one end of each signal line by the switching circuit;
• and
• the settling time is set to respective value of a first settling time group and a second settling time;
• the first settling time group is constituted with a plurality of different time values, each of which is larger than the ratio (C/β0) where C is total capacity, which is, the sum of the parasitic capacity that is parasitic on a single signal line, the holding capacity, and the light emitting element capacity that is parasitic on the light emitting element, and β0 is the reference value of the current amplification factor;
• and the second settling time is constituted with the time value which is shorter than the ratio (C/β0);
• and
• the property parameter acquisition circuit acquires the threshold voltage of the drive transistor for each pixel and the current amplification factor of the pixel drive circuit as a first property parameter in the property parameters based on the values of the plurality of measured voltages acquired by the voltage measurement circuit for the first settling time group;
• and the property parameter acquisition circuit acquires the irregularity parameter that indicates the irregularity of the current amplification factor as a second property parameter in the property parameters based on value of the threshold voltage acquired for each pixel and the value of the measured voltage acquired by the voltage measurement circuit for the second settling time.

A property parameter acquisition method in a pixel driving device for driving a plurality of pixels, connected to each of a plurality of signal lines, and each comprising a light emitting element, and a pixel drive circuit having a drive transistor whose one end of the current path is connected to one terminal of the light emitting element for controlling the current supplied to the light emitting element, the pixel drive circuit having a holding capacity for storing charge determined by voltage impressed on the control terminal of the drive transistor, including;

• a reference voltage impressing step for impressing a reference voltage on one end of each signal line so that the electric potential difference of one end to the other end of the current path of the drive transistor is a value that exceeds the threshold voltage of the drive transistor of one end of each signal line by connecting a voltage impressing circuit to one end of each signal line;
• measurement voltage acquisition step that interrupts the connection between one end of each signal line and the voltage impressing circuit, then acquires a voltage of one end of each signal line as the measured voltage after passage of each of predetermined settling times after interrupting the connection;
• a property parameter acquisition step for acquiring the property parameters that relate to the electrical properties of each pixel from the measured voltages;
• wherein,
• the settling time in the measured voltage acquisition step is set to respective values of a first settling time group and a second settling time;
• the first settling time group is constituted with a plurality of different time values, each of which is larger than the ratio (C/β0) C is total capacity, which is, the sum of the parasitic capacity that is parasitic on a single signal line, the holding capacity, and the light emitting element capacity that is parasitic on the light emitting element, and β0 is the reference value of the current amplification factor, and the second settling time is constituted with the time value which is shorter than the ratio (C/β0);
• and
• the property parameter acquisition step, including:
• a first property parameter acquisition step that acquires the threshold voltage of the drive transistor of each pixel and the current amplification factor of the pixel drive circuit as the first property parameters in the property parameters, based on the values of measured voltages for the first settling time group;
• and
• a second property parameter acquisition step that acquires the irregularity parameter which indicates the irregularity of the current amplification factor as a second property parameter in the property parameters based on the value of the threshold voltage acquired for each pixel and the value of the measured voltage for the second settling time.

A light emitting device, comprising:

• a plurality of pixels, connected to each of a plurality of signal lines, each comprising
• a light emitting element, and
• a drive transistor having a current path and a control terminal, which connects one end of the current path to one terminal of the light emitting element and which controls the electric current supplied to the light emitting element through the current path based on the voltage data written between the control terminal and the one end of the current path;
• a voltage measurement circuit for acquiring a voltage value as a measured voltage of one end of each signal line;
• a property parameter acquisition circuit for acquiring the property parameters that relate to the electrical properties of each pixel;
• wherein,
• the voltage measurement circuit acquires the voltage value of the one end of each signal line, denoted as Vmeas(t) in equation (7), as a plurality of first measured voltages for a plurality of different settling times whose respective values to satisfy the condition (C/β)/t<1 and as a second measured voltage, for a settling time whose value satisfies the condition (C/β)/t≧1, where the settling time is defined as the time elapsed from the time when an impressed voltage is stopped after the voltage is impressed on the one end of the current path of the drive transistor via the one end of each signal line so that the electric potential difference between one end and the other end of the current path of the drive transistor exceeds the threshold voltage of the drive transistor, and then the one end of each signal line is set in a state of high impedance;
• and
• the property parameter acquisition circuit acquires an irregularity parameter (Δβ/β) that indicates the irregularity of the voltage/current properties of the drive transistor of the plurality of pixels, as the property parameter, based on the plurality of first measured voltage values, and the value of the second measured voltage, acquired by the voltage measurement circuit.
• Vmeas
• 
• (
• t
• )
• =
• Vth
• +
• 1
• t
• (
• C
• /
• β
• )
• +
• 1
• Vref
• -
• Vth
• (
• 7
• )
• where, t:
• settling time
• Vmeas(t):
• the measured voltage acquired by the voltage measurement circuit at the elapsed settling time t
• Vth:
• the threshold voltage of the drive transistor
• Vref:
• Reference voltage
• C:
• Total Capacity(C=Cs+Cp+Cel)
• Cs:
• Holding capacity
• Cp:
• Wiring parasitic capacity
• Cel:
• Light emitting element capacity
• β:
• Constant