CONFIDENTIAL
EXTERNAL COMPENSATION FOR HIGH-RESOLUTION AMOLED DISPLAYS
LYNN VERSCHUEREN
CONFIDENTIAL
OVERVIEW
Display Driving Active Matrix
External Compensation Why? 3T2C
Calibration Method Display Characterization
2T1C Calibration Method Display Characterization
Conclusion
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CONFIDENTIAL
DISPLAY DRIVING
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ACTIVE MATRIX
CONFIDENTIAL
OVERVIEW
Display Driving Active Matrix
External Compensation Why? 3T2C
Calibration Method Display Characterization
2T1C Calibration Method Display Characterization
Conclusion
4
CONFIDENTIAL
AMOLED WITH EXTERNAL COMPENSATION
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WHY?
Calibration
• Initial Variations• Bias Stress• OLED Degradation
External
• High Resolution• Improved Accuracy
In-Pixel
AMOLED
• Higher Contrast• Flexibility• Low Power
CONFIDENTIAL
EXTERNAL COMPENSATION FOR HIGH RESOLUTION AMOLED
8T pixel circuit
6
3T pixel circuits:
2T pixel circuit:
US 2017/0148383 A1
US 2007/0195020 A1
This presentation
3T2C
2T1C
IN-PIXEL COMPENSATION EXTERNAL COMPENSATION
CONFIDENTIAL
OVERVIEW
Display Driving Active Matrix
External Compensation Why? 3T2C
Calibration Method Display Characterization
2T1C Calibration Method Display Characterization
Conclusion
7
CONFIDENTIAL
3T2C COMPENSATION PRINCIPLE
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3T2C DUAL-GATE ACTIVE MATRIX
3T2C Pixel CircuitShared Data Line Higher Resolution
CONFIDENTIAL
3T2C COMPENSATION PRINCIPLE
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VBG = -3V
VBG = 3V
CONFIDENTIAL
3T2C COMPENSATION PRINCIPLE
10
MODES OF OPERATION: CALIBRATION
Phase 1: CAL = 0, SEL = 1 DATA1 = reference voltage= 0= 1
= VREF
EP 3 367 374 A1, AN ACTIVE MATRIX DISPLAY AND A METHOD FOR THRESHOLD VOLTAGE COMPENSATION IN AN ACTIVE MATRIX DISPLAY, Genoe J., Verschueren L., De Roose F., Dehaene W.Verschueren L. et al., 40x Current Variation Reduction Enabled by an External VT-Compensation Scheme for AMOLED Displays using a 3T2C-Pixel Circuit with Dual-Gate TFTs, SID digest, pp. 437-440, 2018
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Phase 1: CAL = 0, SEL = 1 DATA1 = reference voltage
Phase 2: CAL = 1, SEL = 0 DATA2 varied I in GND line measured for every VDATA2
Phase 3: Store VDATA2 for which I = Iref
= 1= 0
= Vi
IGND
EP 3 367 374 A1, AN ACTIVE MATRIX DISPLAY AND A METHOD FOR THRESHOLD VOLTAGE COMPENSATION IN AN ACTIVE MATRIX DISPLAY, Genoe J., Verschueren L., De Roose F., Dehaene W.Verschueren L. et al., 40x Current Variation Reduction Enabled by an External VT-Compensation Scheme for AMOLED Displays using a 3T2C-Pixel Circuit with Dual-Gate TFTs, SID digest, pp. 437-440, 2018
3T2C COMPENSATION PRINCIPLEMODES OF OPERATION: CALIBRATION
CONFIDENTIAL12
Normal Operation Calibration Refresh
= 0= 1 = 1= 0
Simple Driving Scheme High Frame RatesEP 3 367 374 A1, AN ACTIVE MATRIX DISPLAY AND A METHOD FOR THRESHOLD VOLTAGE COMPENSATION IN AN ACTIVE MATRIX DISPLAY, Genoe J., Verschueren L., De Roose F., Dehaene W.
Verschueren L. et al., 40x Current Variation Reduction Enabled by an External VT-Compensation Scheme for AMOLED Displays using a 3T2C-Pixel Circuit with Dual-Gate TFTs, SID digest, pp. 437-440, 2018
3T2C COMPENSATION PRINCIPLEMODES OF OPERATION
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3T2C COMPENSATION PRINCIPLE
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SADG QQVGA DISPLAY FOR CHARACTERIZATION
Characterized Area:32x32 Pixels (1024)
DielectricGate
Gate insulator
SD
Glass
Gate insulatorIGZO
Polyimide
Interlayer
CathodeECL
Barrier
Barrier
OLED
BGate
Anode
Drive TFT
TFT SEL
TFT CAL
OLED
GND
Self-Aligned Dual-Gate QQVGA Display 3T2C Pixel
Verschueren L. et al., 40x Current Variation Reduction Enabled by an External VT-Compensation Scheme for AMOLED Displays using a 3T2C-Pixel Circuit with Dual-Gate TFTs, SID digest, pp. 437-440, 2018
CONFIDENTIAL
3T2C COMPENSATION PRINCIPLE
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CURRENT VARIATION OF 1024 PIXELS
With Calibration
µ = 229 nAσ = 22.74 %
µ = 225 nAσ = 0.56 %
Verschueren L. et al., 40x Current Variation Reduction Enabled by an External VT-Compensation Scheme for AMOLED Displays using a 3T2C-Pixel Circuit with Dual-Gate TFTs, SID digest, pp. 437-440, 2018
Without Calibration
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3T2C COMPENSATION PRINCIPLE
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BRIGHTNESS VARIATION OF 1024 PIXELS
Verschueren L. et al., 40x Current Variation Reduction Enabled by an External VT-Compensation Scheme for AMOLED Displays using a 3T2C-Pixel Circuit with Dual-Gate TFTs, SID digest, pp. 437-440, 2018
With CalibrationWithout Calibration
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3T2C COMPENSATION PRINCIPLE
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Without Calibration With Calibration
VARIATION AT MULTIPLE GRAY-LEVELS FOR 1024 PIXELS
Verschueren L. et al., 40x Current Variation Reduction Enabled by an External VT-Compensation Scheme for AMOLED Displays using a 3T2C-Pixel Circuit with Dual-Gate TFTs, SID digest, pp. 437-440, 2018
CONFIDENTIAL17Verschueren L. et al., 40x Current Variation Reduction Enabled by an External VT-Compensation Scheme for AMOLED Displays using a 3T2C-Pixel Circuit with Dual-Gate TFTs, SID digest, pp. 437-440, 2018
3T2C COMPENSATION PRINCIPLEVARIATION AT MULTIPLE GRAY-LEVELS FOR 1024 PIXELS
CONFIDENTIAL
OVERVIEW
Display Driving Active Matrix
External Compensation Why? 3T2C
Calibration Method Display Characterization
2T1C Calibration Method Display Characterization
Conclusion
18
CONFIDENTIAL
EXTERNAL COMPENSATION FOR HIGH RESOLUTION AMOLED
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𝐼𝐼𝐷𝐷𝐷𝐷 =µ ∗ 𝐶𝐶𝑜𝑜𝑜𝑜
2∗𝑊𝑊𝐿𝐿
𝑉𝑉𝐺𝐺𝐷𝐷 − 𝑉𝑉𝑇𝑇 2
Determines light output Data applied
Variations due to process variations, bias
stress, ...β-factor: variations due to process
variations (e.g. over-etch), should not change during operation
Not taken into account in previous implementation
EP 3 570 268 A1, AN ACTIVE MATRIX DISPLAY AND A METHOD FOR DRIVING AN ACTIVE MATRIX DISPLAY, Verschueren L., Myny K., Genoe J., Dehaene W.
CONFIDENTIAL
2T1C COMPENSATION PRINCIPLE
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β-FACTOR VARIATIONS
W
L
𝐶𝐶𝑜𝑜𝑜𝑜 = 𝜀𝜀𝑜𝑜𝑜𝑜𝑡𝑡𝑜𝑜𝑜𝑜
Gate insulator- Thickness = tox- Dielectric constant = εox
Process variations in gate insulator cause variations in Cox
W and L can vary due to process variations(e.g. alignment, over-etch)
β-factor:
𝛽𝛽 =𝜇𝜇 ∗ 𝐶𝐶𝑜𝑜𝑜𝑜
2∗𝑊𝑊𝐿𝐿
Process variations cause variations in β-factor
EP 3 570 268 A1, AN ACTIVE MATRIX DISPLAY AND A METHOD FOR DRIVING AN ACTIVE MATRIX DISPLAY, Verschueren L., Myny K., Genoe J., Dehaene W.
CONFIDENTIAL
2T1C COMPENSATION PRINCIPLE
21EP 3 570 268 A1, AN ACTIVE MATRIX DISPLAY AND A METHOD FOR DRIVING AN ACTIVE MATRIX DISPLAY, Verschueren L., Myny K., Genoe J., Dehaene W.
𝐼𝐼𝐷𝐷𝐷𝐷 = 𝛽𝛽 ∗ (𝑉𝑉𝐺𝐺𝐷𝐷 − 𝑉𝑉𝑇𝑇)2
Measure IDVG of every pixel Fit to TFT formula to extract VT & β
Use formula and extracted VT & β to calculate compensated voltage
Optional: recalibrate only VT
𝑉𝑉𝐺𝐺𝐷𝐷 =𝐼𝐼𝐷𝐷𝐷𝐷𝛽𝛽 + 𝑉𝑉𝑇𝑇
CONFIDENTIAL
OVERVIEW
Display Driving Active Matrix
External Compensation Why? 3T2C
Calibration Method Display Characterization
2T1C Calibration Method Display Characterization
Conclusion
22
CONFIDENTIAL
CONCLUSION
AMOLED with ExeternalCompensation• Higher Contrast• Flexibility• Low Power• High Resolution• Improved Accuracy
3T2C Compensation Method• Variation
Reduction from 23% to 0.56% at Calibration Point
2T1C Compensation Method• Variation Reduced
for all Grey Levels
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EXTERNAL COMPENSATION METHOD FOR AMOLED DISPLAYS
CONFIDENTIAL