JP5771807B2 - Signal processing circuit for light emitting device - Google Patents

Description

  The present invention relates to a signal processing circuit for a light emitting device that performs nonlinear processing such as gamma correction on the light emitting device.

2. Description of the Related Art Conventionally, a technique is known in which light emission output characteristics (non-linear characteristics) on the receiver side are taken into consideration and correction is performed in advance on the transmission side in consideration of the characteristics. For example, many television receivers use a cathode ray tube (CRT) as a display device, and this CRT also has non-linear characteristics. Such a non-linear characteristic is called a gamma characteristic. The non-linear characteristic on the image receiving side can be expressed as y = x ^γ when the input is represented by x and the output is represented by y. This curve is like the input / output characteristics of the light emitting device shown in FIG.

For this reason, on the image transmission side or image reception side, the gamma characteristic of y = x ^{1 / γ} shown in the gamma correction curve in FIG. 11 is added to cancel the CRT gamma characteristic on the image reception side. Through such processing, the television receiver can correct the CRT gamma characteristic and perform linear display as shown in the corrected overall characteristic of FIG.

  Recently, a display device using a light emitting device using a light emitting diode or the like has been proposed. A light-emitting device using a light-emitting element also has input / output characteristics as shown in FIG. 11, which may be gamma corrected. Further, gamma correction is often performed for image processing.

  As described above, when gamma correction processing is performed, for example, as disclosed in Patent Document 1, a video signal is converted into a digital signal once and the gamma correction that satisfies the gamma characteristics stored in the memory is performed. After reading out the data, it was converted to an analog signal and converted into a video signal again, so that the input / output characteristics were in a proportional relationship.

JP-A-6-6820

  However, in the conventional gamma correction processing, as described above, the video signal is once converted into a digital signal and the contents of the gamma correction memory are read out.

  For this reason, a memory for storing gamma correction data is required. Also, the gain is very high near the black level where the signal level of the gamma characteristic is low. If an attempt is made to construct digital hardware according to the conventional word length, a bit drop will inevitably occur. For example, in order to obtain A-bit luminance resolution, input data of (A + 2) bits or more is required. Therefore, in the case of gamma correction by A-bit data input, the luminance resolution is reduced to about (A-2) bits.

  In addition, if the word length is increased in order to prevent the deterioration of the luminance resolution, the subsequent processing is affected, and the circuit scale is greatly increased.

  The present invention was devised to solve the above-described problems, and prevents deterioration in luminance resolution without increasing the number of bits of input data, and corrects non-linearity with a simple circuit configuration. An object of the present invention is to provide a signal processing circuit for a light-emitting device that can be used.

In order to achieve the above object, a signal processing circuit for a light-emitting device according to the present invention is a signal processing circuit for a light-emitting device that changes the luminance level of the light-emitting device by changing the pulse width supplied to a drive circuit connected to the light-emitting device A pulse width modulation circuit that holds an input luminance signal and determines an output pulse width based on the luminance signal and an input nonlinear waveform signal, and supplies the pulse signal to the drive circuit; A non-linear waveform signal generating circuit for generating a non-linear waveform signal, wherein the non-linear waveform signal has a non-linearity in a linear portion of a triangular wave, and the non- linear waveform signal generating circuit includes the capacitor of the triangular wave generating circuit using a capacitor. It is composed of a non-linear capacitor. Alternatively, the nonlinear waveform signal generation circuit is configured by a full-wave rectification circuit using a sine wave output from the sine wave generation circuit. Alternatively, the nonlinear waveform signal generation circuit is configured by a synchronous detection circuit using a sine wave output from the sine wave generation circuit .

  According to the present invention, the luminance level of the light emitting device is changed by a change in the pulse width supplied to the drive circuit, and the pulse width modulation circuit for supplying a pulse to the drive circuit holds the input luminance signal. Since the output pulse width is determined based on the luminance signal and the input nonlinear waveform signal, the output pulse width of the pulse width modulation circuit changes depending on the level of the luminance signal. On the other hand, since the non-linear waveform signal input to the pulse width modulation circuit is a signal having nonlinearity in the linear part of the triangular wave, the rate of change of the output pulse width of the pulse width modulation circuit is not linear but nonlinear, The same effect as gamma correction can be obtained.

It is a figure which shows the circuit structure of the principal part of the signal processing circuit for light-emitting devices of this invention. It is a figure which shows the time chart for demonstrating operation | movement of the circuit of FIG. It is a figure which shows the circuit structure which produces | generates the signal waveform which gave the nonlinearity to the linear part of the triangular waveform. It is a figure which shows the circuit structure which produces | generates a triangular waveform signal. FIG. 4 is a diagram showing an output signal waveform when the signal of FIG. 3A is input to the circuit of FIG. 1 and the data stored in the capacitor 9 is changed. FIG. 5 is a diagram illustrating an output signal waveform when the signal of FIG. 4A is input to the circuit of FIG. 1 and the data stored in the capacitor 9 is changed. It is a figure which shows the circuit structure which produces | generates a nonlinear signal. It is a figure which shows the input waveform and output waveform of the circuit of FIG. It is a figure which shows the circuit structure which produces | generates a nonlinear signal. It is a figure which shows the example of the signal waveform which gave the nonlinearity of the power to the linear part of a triangular wave. It is a figure which shows the input / output characteristic of a light-emitting device, a gamma correction curve, and the comprehensive characteristic after correction | amendment. It is a figure which shows the circuit structural example of a sine wave generation circuit.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. The drawings relating to the structure are schematic, and there may be a case where portions having different dimensional relationships and ratios are included between the drawings.

  For example, a light-emitting device in which light-emitting elements such as light-emitting diodes are arranged two-dimensionally includes an active matrix circuit and a passive matrix circuit. FIG. 1 shows a circuit configuration corresponding to one pixel among them. .

  FIG. 1 also shows a circuit configuration example of the main part of the signal processing circuit for a light emitting device according to the present invention, which is composed of a pixel circuit 12 and a driver circuit 11. The pixel circuit 12 includes a capacitor 9, an inverter 1, an FET 2, an FET 3, an FET 4, a light emitting element 5 such as a light emitting diode, an FET 6, an FET 7, a capacitor 9, and a capacitor 10. Here, FETs 2, 3, 6, and 7 are N-type MOS transistors, and FET 4 is a P-type MOS transistor. The driver circuit 11 includes a constant current source 8.

  The inverter 1 includes, for example, a P-type MOS FET 1a and an N-type MOS FET 1b, as shown in FIG.

  As shown by the broken line in FIG. 1, the pixel circuit 12 includes a pulse width modulation circuit 12 a including a capacitor 9, an inverter 1, and an FET 2, and a current driving circuit for a light emitting element 5 including an FET 3, FET 4, FET 6, FET 7, and a capacitor 10. 12b. The pulse width modulation circuit 12a generates pulse signals having different pulse widths from the input signal, and the current drive circuit 12b is a current equalization circuit, and reduces variations in the drive current of the FET 4.

  Here, the operation will be described with reference to the time chart of FIG. As shown in FIG. 2, the operation of the pixel circuit 12 includes an operation in the data program period and an operation in the light emission period in a sequence, and the pixel circuit 12 is operated by repetition of these two periods.

  First, the data program period of the pulse width modulation circuit 12a will be described. If the input signal Vsig is input as shown in FIG. 2, the DC component is removed by the capacitor 9 and input to the inverter 1. The inverter 1 is a self-bias type inverter and has a threshold voltage Vsb. When the Vscan signal is applied to the gate of the FET 2, the input side and the output side of the inverter 1 are short-circuited by the FET 2, so that the difference between Vsig (ie, Vdata) and Vsb in the Vscan signal period is charged in the capacitor 9.

  Next, when the operation in the light emission period is executed, a Sweep Wave (triangular wave) is supplied to the Vsig line. Seep Wave passes through the capacitor 9 and reaches Vin. However, the gate voltage of the FET 2 is at a low level, and the FET 2 is off. Further, since the capacitor 9 is charged with the difference (Vdata−Vsb) between Vdata and Vsb as described above, a signal obtained by subtracting (Vdata−Vsb) from the Sweep Wave appears. Here, since a negative level signal at Vin is inverted and appears as a positive signal at the output Vout of the inverter 1, the signal has a pulse width as shown in the figure. That is, with (Vdata−Vsb) as a threshold, the Sweep Wave signal on the negative side of this value appears as a positive pulse signal.

  During the data program period of the current drive circuit 12b, the FET 6 that is the drive current write transistor and the FET 7 that is the current supply transistor are on. The voltage Vprg is a voltage charged in the capacitor 10. Further, the current Itft is substantially equal to Isup flowing through the constant current source 8. The current Isup is sufficient to charge the capacitor 10 and the entire pixel circuit, and Vprg and Vpx are fixed.

  In the light emission period, the following operation is performed. Since the capacitor 10 is charged and Vprg is supplied to the gate of the FET 4 which is the driving transistor, the FET 4 reaches the saturation region. The current Itft is unchanged and maintains a constant current. Here, the current Ioled is approximately equal to the current Isup. When the input signal Vsig is input, Vscan, Vsig, Vdd, GND, the cathode side voltage Vcat of the light emitting element 5 and the like are necessary to see the current flow of the light emitting element 5 of the pixel circuit 12.

  As described above, in the light emission period, the FET 3 is turned on during a period in which a positive pulse appears in Vout, and the current Itft and the current Ioled (period τoled) flow. During this period, the light emitting element 5 is turned on. Driven to emit light. Therefore, the luminance of the light emitting element 5 can be changed by changing the positive pulse width W appearing at Vout. For example, increasing the pulse width W increases the luminance, and decreasing the pulse width W decreases the luminance.

  In order to change the luminance of the light emitting element 5 by changing the pulse width W in this way, the value of (Vdata−Vsb) written in the capacitor 9 is changed to a predetermined LUT (lookup table) or the like during the data program period. A method of replacing with the above can be considered. When (Vdata−Vsb) is changed, the threshold value for the Deep Wave input to Vsig during the light emission period changes, so that the pulse width W changes.

  Therefore, a luminance signal may be input to Vsig during the data program period. In this case, of the (Vdata−Vsb) written in the capacitor 9, Vdata corresponds to a luminance signal.

  Even if (Vdata−Vsb) written to the capacitor 9 is constant during the data program period, if the shape of the Deep Wave input to Vsig during the light emission period, for example, the pulse width of a triangular wave, changes. The pulse width W changes corresponding to.

  Here, when performing gamma correction of a luminance signal in a light emitting display device or the like, it is used that the luminance of the light emitting element 5 can be controlled by the length of the pulse width. Therefore, the curve shown in FIG. 3A is input to the input signal Vsig of the circuit of FIG. 1 instead of the triangular wave shown in the Sweep Wave of FIG. As a comparison, a triangular wave is shown in FIG. As shown in FIG. 4A, the triangular wave is a linear signal in which the regions R1 and R2 constituting the triangle are straight lines.

  On the other hand, in the signal shown in FIG. 3A, the S1 and S2 regions constituting the signal are not straight lines but are non-linear (curved), so this signal is a non-linear signal. The curve shown in FIG. 3A is a curve of S1 and S2 by giving nonlinearity to the linear portions of R1 and R2 of the triangular wave of FIG. 4A. The portion S2 is equivalent to the curve of the gamma correction curve in FIG. 11, and the portion S1 corresponds to a curve in which the gamma correction curve in FIG.

  FIG. 5 and FIG. 6 show how the Vout and Ioled output waveforms in FIG. 1 change due to the difference in the input waveforms. FIG. 5 shows the result of inputting the waveform of FIG. 3A to Vsig of FIG. 1, and FIG. 6 shows the result of inputting the waveform of FIG. 4A to Vsig of FIG. First, with respect to Vdata during the data program period, the DC level was changed stepwise by a certain value. Next, when the waveform of FIG. 3A is input to Vsig of FIG. 1, the waveform shape of FIG. 3A is not changed, and the same DC level as the change of the DC level of Vdata is input. In addition, when the waveform of FIG. 4A is input to Vsig of FIG. 1, the DC shape that is input at the same DC level as the change of the DC level of Vdata without changing the shape of the waveform of FIG. The level was input in steps of a certain value.

  5 and 6, the left side is a data program period signal, and the right side is a light emission period signal.

  5 and 6, the same signals Vscan, Vdata, Vsb, Itft, and Isup are used during the data program period. FIGS. 5 and 6 show the pulse width of the signal during the light emission period, along with a constant change in the DC level of Vsig for both Vout and Ioled. Since the DC level of Vsig is changed step by step by a certain value, this change is a linear change. With respect to this change, the change in pulse width at Vout and Ioled in FIG. 6 is uniform.

  Thus, the input / output characteristics are linear. On the other hand, in FIG. 5, changes in the pulse widths of Vout and Ioled are not uniform. That is, while the pulse width is small, the increase rate of the pulse width is small, but as the pulse width increases, the increase rate of the pulse width gradually increases. Thus, in the case of the waveform shown in FIG. 3A, the input / output characteristics are non-linear, and the characteristics are substantially equivalent to the gamma correction curve.

  Therefore, a luminance signal for the light emitting element 5 is input to the signal Vsig in the data program period to obtain a Vdata signal written to the capacitor 9, and then a triangular wave as shown in FIG. When a signal with non-linearity is input to the linear portion, the input / output characteristics of the luminance signal become non-linear and close to gamma characteristics. This is because, as described above, the waveform in FIG. 3A is a waveform obtained by combining two gamma correction curves that are symmetric with respect to the y-axis. For this reason, the input / output characteristics are improved by the same effect as the gamma correction.

The gamma correction can be expressed as y = x ^{1 / γ} as described above. The curve of the gamma correction curve changes depending on (1 / γ) which should be x. This can be achieved by making the Vsig signal in the light emission period of FIG. 1 as shown in FIG. Corresponds to the gamma characteristic curve when the power of x (power (1 / γ)) is changed by changing the pulse width and the curve shape of the non-linear portion as in the waveforms of P1, P2, and P3. Can be made.

  As described above, FIG. 3B shows a circuit for creating a signal waveform having such a shape that two symmetrical gamma curves are combined. FIG. 3B is a circuit in which a capacitor of a triangular wave generation circuit using a capacitor is a non-linear capacitor. This circuit includes a constant current source 21, a P-type MOS transistor FET 22, an N-type MOS transistor FET 23, a constant current source 24, and a non-linear capacitor 25. As the nonlinear capacitor 25, a ferroelectric capacitor or the like is used. The drain terminal of the FET 22 is connected to the constant current source 21, and the source terminal is connected to the drain terminal of the FET 23 and the nonlinear capacitor.

  The gate of the FET 22 and the gate of the FET 23 are connected. When a rectangular pulse as shown in the figure is input to the input terminal to which the gate of the FET 22 and the gate of the FET 23 are connected, when the input signal is in a low level state, the FET 23 is turned off and the FET 22 is turned on. Then, the current of the constant current source 21 flows through the FET 22 and charges the nonlinear capacitor 25. For this reason, in the initial state, the nonlinear capacitor 25 is charged to a predetermined voltage.

  Next, when the input signal becomes high level, the FET 22 is turned off, while the FET 23 is turned on. For this reason, charging of the non-linear capacitor is stopped and current flows in the direction of the constant current source 24 by the FET 23. Thereby, the non-linear capacitor 25 is discharged. However, the non-linear capacitor 25 is discharged in a non-linear manner and is not discharged at a constant rate, so that the non-linear capacitor 25 has a curved shape like the portion S1 in FIG.

  Next, when the input signal changes from the high level to the low level, the FET 23 is turned off, while the FET 22 is turned on. For this reason, the discharge of the non-linear capacitor 25 stops and the non-linear capacitor 25 is charged by the current of the constant current source 21 via the FET 22. As in the previous discharge process, the non-linear capacitor 25 is charged in a non-linear manner and is not charged at a constant rate, and thus has a curved shape as shown by S2 in FIG. As described above, the nonlinear signal waveform shown in FIG. 3A is formed. It should be noted that in order to have the above-described power non-linearity, those having different charge / discharge characteristics of the non-linear capacitor 25 may be used.

  On the other hand, FIG. 4B shows a circuit for creating the triangular waveform of FIG. The circuit configuration relating to the constant current source 51, FET 52, FET 53, and constant current source 54 is the same as in FIG. Here, the difference from FIG. 3B is that the capacitor 55 is not a non-linear capacitor but a linear capacitor that is usually used. Since the charging and discharging operations of the linear capacitor are performed linearly, as shown in FIG. 3A, when the capacitor 55 is performing the discharging operation, the capacitor is discharged at a constant rate, like the portion R1. It becomes a linear shape. Further, when the capacitor 55 is performing the charging operation, the capacitor 55 is charged at a constant rate, and thus has a linear shape like the portion R2.

  Next, FIG. 7 shows another circuit configuration for generating the signal waveform of FIG. The circuit in FIG. 7 is a full-wave rectifier circuit including a sine wave oscillation circuit 35, a diode group 30, and a resistor 36. The diode group 30 includes diodes 31 to 34. The output of the sine wave oscillation circuit 35 becomes a sine wave as shown in FIG. In the sine wave of FIG. 8A, current flows through the diode 31 and the diode 33 during the positive voltage period. A voltage having the same shape as the positive voltage period of the sine wave in FIG. 8A is generated at both ends of the resistor 36. On the other hand, current flows through the diode 32 and the diode 34 during the negative voltage period. A voltage having a shape obtained by inverting the voltage in the negative voltage period of the sine wave of FIG. 8A is generated at both ends of the resistor 36. As described above, the signal waveform of FIG. 8B can be obtained. It should be noted that in order to give the power nonlinearity described above, the amplitude and frequency of the sine wave output from the sine wave oscillation circuit 35 may be changed.

  Further, another waveform generation circuit is shown in FIG. The circuit in FIG. 9 is a synchronous detection circuit, and includes a sine wave oscillation circuit 40, a non-inverting amplifier 41, an inverting amplifier 42, an inverter 43, analog switches 44 and 45, and a comparator 46. The output of the sine wave oscillation circuit 40 is connected to the input of the non-inverting amplifier 41, the input of the inverting amplifier 42, and the input of the comparator 46. The output of the non-inverting amplifier 41 is connected to the input of the analog switch 44, and the output of the inverting amplifier 42 is connected to the input of the analog switch 45. The output of the comparator 46 is connected to the input of the inverter 43 and the control terminal of the analog switch 44. The output of the inverter 43 is connected to the control terminal of the analog switch 45. Further, the analog switch 44 and the analog switch 45 are connected to become an output signal of the synchronous detection circuit.

  When the sine wave signal from the sine wave oscillation circuit 40 is input to the non-inverting amplifier 41, the inverting amplifier 42, and the comparator 46, first, during the positive voltage period of the sine wave, the non-inverting amplifier 41 generates a positive voltage signal. Output from the non-inverting amplifier 41. Further, the positive voltage signal is inverted by the inverting amplifier 42 to become a negative voltage signal, and is output from the inverting amplifier 42. On the other hand, since the sine wave signal is also input to the comparator 46, the output of the comparator 46 during the positive voltage period of the sine wave signal becomes a high level pulse signal.

  This high level signal drives the analog switch 44 to make the analog switch 44 conductive, and a positive voltage signal output from the non-inverting amplifier 41 is output via the analog switch 44. On the other hand, since the analog switch 45 is applied with a low level signal obtained by inverting the output of the comparator 46 by the inverter 43, the analog switch 45 is not turned on and the negative voltage signal output from the inverting amplifier 42 is not output.

  Next, during a sine wave negative voltage period, the output of the non-inverting amplifier 41 is a negative voltage signal, the output of the inverting amplifier 42 is a positive voltage signal, and the output of the comparator 46 is a low level signal. The analog switch 44 is turned off by this low level signal, and the output of the non-inverting amplifier 41 is not output from the analog switch 44. On the other hand, since the output of the comparator 46 is inverted by the inverter 43 to become a high level signal, the analog switch 45 becomes conductive, and the positive voltage signal output from the inverting amplifier 42 is output from the analog switch 45.

  As described above, an output signal similar to the output of the full-wave rectifier circuit of FIG. 7 is obtained. This waveform is shown as Vsig in FIG. In order to give the power nonlinearity described above, the amplitude and frequency of the sine wave output from the sine wave oscillation circuit 40 may be changed.

  Next, FIG. 12 shows a circuit configuration example of the sine wave oscillation circuits 35 and 40 described with reference to FIGS. FIG. 12 shows a Wien bridge oscillation circuit. An operational amplifier 61, resistors 60, 62, 63 and 65, and capacitors 64 and 66 are included. On the positive feedback side of the operational amplifier 61, a capacitor 66 and a resistor 65 connected in series to the output of the operational amplifier 61, and a bandpass filter composed of a resistor 63 and a resistor 64 connected in parallel between the resistor 65 and GND are configured. ing. This band pass filter passes only the frequency band to be oscillated. On the other hand, the negative feedback side includes a resistor 62 and a resistor 60 that determine the non-inverting amplification factor of the operational amplifier 61.

  The resistance values of the resistors 60, 62, 63, and 65 are R4, R3, R2, and R1, respectively, and the capacitances of the capacitors 64 and 66 are C2 and C1, respectively. Since the non-inverting amplification factor A of the operational amplifier 61 is equal to (1+ (R3 / R4)), the amplitude of the sine wave output can be changed by changing the amplification factor A. The oscillation condition of the Wien bridge oscillation circuit is amplification factor A ≧ 3.

On the other hand, the frequency condition f of the sine wave by the band-pass filter on the positive feedback side can be expressed as f = 1 / (2π (C1C2R1R2) ^1/2 ). Here, if the same value of capacitance as C1 = C2 = C0 is used and the same resistance value as R1 = R2 = R0 is used, then f = 1 / (2πR0C0).

  As described above, the Wien bridge oscillation circuit is applied to the sine wave oscillation circuits 35 and 40, and the amplitude of the sine wave output can be changed by changing the ratio of R3 and R4, and C1, C2, R1 The frequency of the sine wave output can be changed by changing the value of R2. As a result, the circuits of FIGS. 7 and 9 can have power nonlinearity as shown in FIG.

  As described above, the input / output of the light emitting element 5 can be changed nonlinearly, and gamma correction can be performed. Therefore, as a circuit of FIG. 1 and a circuit for generating a non-linear waveform signal, a circuit for one pixel is configured by selecting and using FIGS. 3, 7, 9 and the like, and if these are arranged two-dimensionally, gamma correction is performed. A light-emitting device that can be processed can be obtained.

  The configuration of the signal processing circuit of the light-emitting device of the present invention can be applied particularly to the improvement of input / output characteristics of a display device having a light-emitting element.

1 Inverter 1a FET
1b FET
2 FET
3 FET
4 Capacitor 5 FET
6 Capacitor 7 FET
8 Constant current source 9 Capacitor 10 Capacitor 11 Power supply voltage circuit 12 Pixel circuit

Claims (9)

A signal processing circuit for a light emitting device that changes a luminance level of the light emitting device by a change in a pulse width supplied to a drive circuit connected to the light emitting device,
A pulse width modulation circuit that holds an input luminance signal and determines an output pulse width based on the luminance signal and an input nonlinear waveform signal, and supplies the pulse signal to the driving circuit;
A non-linear waveform signal generating circuit for generating the non-linear waveform signal,
The nonlinear waveform signal has nonlinearity in the linear part of the triangular wave ,
The signal processing circuit for a light-emitting device, wherein the nonlinear waveform signal generation circuit includes the capacitor of a triangular wave generation circuit using a capacitor .   A signal processing circuit for a light emitting device that changes a luminance level of the light emitting device by a change in a pulse width supplied to a drive circuit connected to the light emitting device,
  A pulse width modulation circuit that holds an input luminance signal and determines an output pulse width based on the luminance signal and an input nonlinear waveform signal, and supplies the pulse signal to the driving circuit;
  A non-linear waveform signal generating circuit for generating the non-linear waveform signal,
  The nonlinear waveform signal has nonlinearity in the linear part of the triangular wave,
  The signal processing circuit for a light-emitting device, wherein the nonlinear waveform signal generation circuit is configured by a full-wave rectification circuit using a sine wave output from a sine wave generation circuit.   A signal processing circuit for a light emitting device that changes a luminance level of the light emitting device by a change in a pulse width supplied to a drive circuit connected to the light emitting device,
  A pulse width modulation circuit that holds an input luminance signal and determines an output pulse width based on the luminance signal and an input nonlinear waveform signal, and supplies the pulse signal to the driving circuit;
  A non-linear waveform signal generating circuit for generating the non-linear waveform signal,
  The nonlinear waveform signal has nonlinearity in the linear part of the triangular wave,
  The signal processing circuit for a light emitting device, wherein the nonlinear waveform signal generation circuit is configured by a synchronous detection circuit using a sine wave output from a sine wave generation circuit. 4. The signal processing circuit for a light emitting device according to claim 2, wherein the sine wave generation circuit can appropriately set the frequency and amplitude of the output sine wave. 5. The signal processing circuit for a light-emitting device according to claim 4, wherein the sine wave generation circuit is a Wien bridge oscillation circuit. 6. The signal processing circuit for a light emitting device according to claim 1, wherein the linear part of the triangular wave is provided with nonlinearity of power. The pulse width modulation circuit operates in a first operation period in which the input luminance signal is held and a second operation period in which the nonlinear waveform signal is input and a pulse signal whose pulse width is changed is output. The signal processing circuit for a light-emitting device according to any one of claims 1 to 6, wherein The signal processing circuit for a light-emitting device according to claim 1, wherein the light-emitting device includes a light-emitting element and changes a luminance level of the light-emitting element. The signal processing circuit for a light emitting device according to claim 8, wherein the light emitting element is a light emitting diode.

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