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

A light emitting device, comprising:

• at least one pixel, connected to at least one signal line, and 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 a current path of the drive transistor connected to one terminal of the light emitting element as well as holding capacity for storing charge by a voltage impressed on a current control terminal of the drive transistor;
• a voltage impressing circuit for outputting a reference voltage;
• a voltage measurement circuit;
• a switching circuit for switching connection of one end of the signal line, and the voltage measurement circuit;
• and
• a property parameter acquisition circuit for acquiring the property parameters that relate to the electrical properties of the pixel;
• wherein,
• the reference voltage has an electric potential in which the electric potential difference between the one end and 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 the signal line to the voltage impressing circuit and sets the connection between the one end of the signal line and the voltage impressing circuit being interrupted after impressing the reference voltage for a predetermined time on the one end of the signal line by the voltage impressing circuit, and connects the one end of the signal line to the voltage measurement circuit subsequent to a predetermined settling time elapsing;
• and
• the voltage measurement circuit acquires the voltage value of the one end of the signal line as the measured voltage when being connected to the one end of the signal line by the switching circuit;
• and
• the property parameter acquisition circuit acquires the threshold voltage of the drive transistor and the current amplification factor of the pixel drive circuit as property parameters based on the values of the plurality of measured voltages acquired by the voltage measurement circuit for the plurality settling times.

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

• a reference voltage impressing step for impressing a reference voltage on one end of the 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 transistorby connecting a voltage impressing circuit to the one end of the signal line;
• a measurement voltage acquisition step that interrupts the connection between one end of the signal line and the voltage impressing circuit, then acquires the voltages, as a plurality of measured voltages, of one end of the signal line after elapsing of each of a predetermined plurality of differing settling times after the interruption;
• and
• a property parameter acquisition step that acquires the threshold voltage of the drive transistor and the current amplification factor of the pixel drive circuit as property parameters based on the values of the plurality of measured voltages acquired for the plurality of settling times.

A light emitting device, comprising:

• a pixel, connected to a signal line, having a light emitting element, a drive transistor having a current path and 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, and a holding capacity for storing charge determined by the voltage impressed on the drive transistor;
• a voltage measurement circuit for acquiring a voltage value as a measured voltage of one end of the signal line;
• and
• a property parameter acquisition circuit for acquiring the property parameters that relate to the electrical properties of the pixel;
• wherein,
• the voltage measurement circuit acquires the voltage value of the voltage of the one end of the signal line indicated in equation (4), as the measured voltage, after voltage is impressed between both ends of the current path of the drive transistor via the one end of the signal line so as to exceed the threshold voltage of the drive transistor when the elapsed time from the moment the impressed voltage is stopped by the existence of a high impedance state becomes the settling time t, and when C is total capacity, which is the sum of the holding capacity of the pixel connected by the signal line, the parasitic capacity that is parasitic on the signal line, and the light emitting element capacity that is parasitic on the light emitting element;
• and
• the property parameter acquisition circuit acquires the threshold voltage of the drive transistor and the (C/β) value as property parameters based on the plurality of measured voltages acquired by the measurement circuit when the settling time t is a plurality of differing values that satisfy the condition of (C/β)/t<1.
• Vmeas
• 
• (
• t
• )
• =
• Vth
• +
• 1
• t
• (
• C
• /
• β
• )
• +
• 1
• Vref
• -
• Vth
• (
• 4
• )
• 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+Ce1)
• Cs:
• Holding capacity
• Cp:
• Wiring parasitic capacity
• Ce1:
• Light emitting element capacity
• β:
• Constant