external compensation for high-resolution amoled displays€¦ · external compensation for high...

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EXTERNAL COMPENSATION FOR HIGH-RESOLUTION AMOLED DISPLAYS

LYNN VERSCHUEREN

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OVERVIEW

Display Driving Active Matrix

External Compensation Why? 3T2C

Calibration Method Display Characterization

2T1C Calibration Method Display Characterization

Conclusion

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DISPLAY DRIVING

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ACTIVE MATRIX

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OVERVIEW





Conclusion

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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

Presenter

Presentation Notes

AMOLED: uses TFT as analog current source, so VT differences nonuniformity Calibration: 2 options: internal (in-pixel) calibration and external calibration In pixel: requires more TFTs larger pixels lower resolution External: minimal #TFTs + compensation in c-Si high resolution + accuracy

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EXTERNAL COMPENSATION FOR HIGH RESOLUTION AMOLED

8T pixel circuit

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3T pixel circuits:

2T pixel circuit:

US 2017/0148383 A1

US 2007/0195020 A1

This presentation

3T2C

2T1C

IN-PIXEL COMPENSATION EXTERNAL COMPENSATION

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OVERVIEW





Conclusion

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3T2C COMPENSATION PRINCIPLE

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3T2C DUAL-GATE ACTIVE MATRIX

3T2C Pixel CircuitShared Data Line Higher Resolution

Presenter

Presentation Notes

Dual gate: voltage on BG shifts VT

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VBG = -3V

VBG = 3V

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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

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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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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


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CURRENT VARIATION OF 1024 PIXELS

With Calibration

µ = 229 nAσ = 22.74 %

µ = 225 nAσ = 0.56 %


Without Calibration

Presenter

Presentation Notes

Without calibration = fixed BG Note: scale: horizontal is same scale, vertical scale is very different (~factor 25)

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BRIGHTNESS VARIATION OF 1024 PIXELS


With CalibrationWithout Calibration

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Without Calibration With Calibration

VARIATION AT MULTIPLE GRAY-LEVELS FOR 1024 PIXELS


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

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OVERVIEW





Conclusion

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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.

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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.

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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

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OVERVIEW





Conclusion

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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

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external compensation for high-resolution amoled displays€¦ · external compensation for high...

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