Journal of the Institute of Electronics and Information Engineers (전자공학회논문지)

The Institute of Electronics and Information Engineers (대한전자공학회)
권호 표지
DOI QR코드

DOI QR Code

An Area-Efficient Time-Shared 10b DAC for AMOLED Column Driver IC Applications

AMOLED 컬럼 구동회로 응용을 위한 시분할 기법 기반의 면적 효율적인 10b DAC

  • Kim, Won-Kang (Dept. of Electronic Engineering, Sogang University) ;
  • An, Tai-Ji (Dept. of Electronic Engineering, Sogang University) ;
  • Lee, Seung-Hoon (Dept. of Electronic Engineering, Sogang University)
  • Received : 2016.01.25
  • Accepted : 2016.04.28
  • Published : 2016.05.25
Download PDF
⟨ Previous Next ⟩

Abstract

This work proposes a time-shared 10b DAC based on a two-step resistor string to minimize the effective area of a DAC channel for driving each AMOLED display column. The proposed DAC shows a lower effective DAC area per unit column driver and a faster conversion speed than the conventional DACs by employing a time-shared DEMUX and a ROM-based two-step decoder of 6b and 4b in the first and second resistor string. In the second-stage 4b floating resistor string, a simple current source rather than a unity-gain buffer decreases the loading effect and chip area of a DAC channel and eliminates offset mismatch between channels caused by buffer amplifiers. The proposed 1-to-24 DEMUX enables a single DAC channel to drive 24 columns sequentially with a single-phase clock and a 5b binary counter. A 0.9pF sampling capacitor and a small-sized source follower in the input stage of each column-driving buffer amplifier decrease the effect due to channel charge injection and improve the output settling accuracy of the buffer amplifier while using the top-plate sampling scheme in the proposed DAC. The proposed DAC in a $0.18{\mu}m$ CMOS shows a signal settling time of 62.5ns during code transitions from '$000_{16}$' to '$3FF_{16}$'. The prototype DAC occupies a unit channel area of $0.058mm^2$ and an effective unit channel area of $0.002mm^2$ while consuming 6.08mW with analog and digital power supplies of 3.3V and 1.8V, respectively.

본 논문에서는 시분할 기법을 적용하여 AMOLED 컬럼 구동회로용 DAC의 유효 채널 면적을 최소화한 2단 저항 열 기반의 10비트 DAC를 제안한다. 제안하는 DAC는 시분할 기법 기반의 DEMUX, 6비트 및 4비트의 2단 저항 열 구조를 기반으로 하는 롬 구조의 디코더를 2단계로 사용하여 기존의 디스플레이용 DAC보다 빠른 변환속도를 가지는 동시에 하나의 패널 컬럼 구동을 위한 DAC의 유효 면적을 최소화하였다. 두 번째 단 4비트 저항 열에서는 DAC 채널의 면적과 부하 영향을 줄이는 동시에 버퍼 증폭기로 인한 채널 간 오프셋 부정합을 제거하기 위해 기존의 단위-이득 버퍼 대신 간단한 구조의 전류원으로 대체하였다. 제안하는 1:24 DEMUX는 하나의 클록과 5비트 2진 카운터만을 사용하여, 하나의 DAC 채널이 24개의 컬럼을 순차적으로 구동할 수 있도록 하였다. 각 디스플레이 컬럼을 구동하는 출력 버퍼 입력 단에는 0.9pF의 샘플링 커패시터와 작은 크기의 source follower를 추가하여 top-plate 샘플링 구조를 사용하면서 채널 전하 주입에 의한 영향을 최소화하는 동시에 출력 버퍼의 신호정착 정확도를 향상시켰다. 제안하는 DAC는 $0.18{\mu}m$ CMOS 공정으로 제작하였으며, DAC 출력의 정착 시간은 입력을 '$000_{16}$'에서 '$3FF_{16}$'으로 인가했을 때 62.5ns의 수준을 보인다. 제안하는 DAC 단위 채널의 면적 및 유효 채널 면적은 각각 $0.058mm^2$ 및 $0.002mm^2$이며, 3.3V의 아날로그 및 1.8V의 디지털 전원 전압에서 6.08mW의 전력을 소모한다.

Keywords

References

  1. K. Yoneda, R. Yokoyama, and T. Yamada, "Development Trends of LTPS TFT LCDs for Mobile Applications," in Symp. VLSI Circuits Dig. Tech. Papers, pp. 85-90, June 2001.
  2. K. M. Kim, et al, "One-Chip Driver IC for 16 Million Color WXGA LTPS TFT LCD Panel," in SID Symposium Dig. Tech. Papers, May 2008, vol. 39, no. 1, pp. 1391-1393.
  3. C. W Lu, C. C. Shen and W. C. Chen, "An Area-Efficient Fully R-DAC-Based TFT-LCD Column Driver," IEEE TCAS I: Regular Papers, vol. 57, no. 10, pp. 2588-2601, Oct. 2010.
  4. J. H. Kim, B. D. Choi, and O. K. Kwon, "1-billion-color TFT LCD TV with full HD format," IEEE Trans. Consumer Electronics, vol. 51, no. 4, pp. 1042-1050, Nov. 2005. https://doi.org/10.1109/TCE.2005.1561823
  5. J. S. Shim, B. D. Choi, "Design of 8-bit DAC for TFT-LCD Data Driver ICs: Trade-off between Speed and Circuit Area," IEEK Fall Conference, pp. 663-666, Nov. 2013.
  6. Y.-C. Sung, S.-M. So, J.-K. Kim, and O.-K. Kwon, "10bit Source Driver with ResistorResistor-String Digital to Analog Converter," in SID Symp. Dig. Tech. Papers, Jun. 2005, pp. 1099-1101.
  7. M. J. Bell, "An LCD column driver using a switch capacitor DAC," IEEE J. Solid-State Circuits, vol. 40, no. 12, pp. 2756-2765, Dec. 2005. https://doi.org/10.1109/JSSC.2005.858481
  8. Y.-J. Jeon, H.-M. Lee, S.-W. Lee, G.-H. Cho, H.-R. Kim, Y.-K. Choi, and M. Lee, "A Piecewise Linear 10 Bit DAC Architecture With Drain Current Modulation for Compact LCD Driver ICs," IEEE J. Solid-State Circuits, vol. 44, no. 12, pp. 3659-3675, Dec. 2009. https://doi.org/10.1109/JSSC.2009.2035547
  9. C.-W. Lu, C.-M. Hsiao, and P.-Y. Yin, "A 10-b Two-Stage DAC with an Area-Efficient Multiple-Output Voltage Selector and a Linearity-Enhanced DAC-Embedded Op-Amp for LCD Column Driver ICs," IEEE J. Solid- State Circuits, vol. 48, no. 6, pp. 1475-1486, Jun. 2013. https://doi.org/10.1109/JSSC.2013.2252525
  10. K.-D. Kim, et al, "A 10-bit Linear R-string DAC Architecture for Mobile Full-HD AMOLED Driver ICs," in SID Symposium Dig. Tech. Papers, June 2013, vol. 44, no. 1, pp. 469-472.
  11. C.-W. Lu, P.-Y. Yin, C.-M. Hsiao, and M.-C. F. Chang, "A 10b Resistor-Resistor-String DAC with Current Compensation for Compact LCD Driver ICs," in ISSCC Dig. Tech. Papers, pp. 318-320, Feb. 2011.
  12. C.-W. Lu, P.-Y. Yin, C.-M. Hsiao, M.-C. F. Chang, and Y.-S. Lin, "A 10-bit ResistorFloating -Resistor-String DAC (RFR-DAC) for High Color-Depth LCD Driver ICs," IEEE J. Solid-State Circuits, vol. 47, no. 10, pp. 2454-2466, Oct. 2012. https://doi.org/10.1109/JSSC.2012.2206684
  13. R. Hogervorst, et al., "A Compact PowerEfficient 3V CMOS Rail-to-Rail Input/ Output Operational Amplifier for VLSI Cell Libraries," IEEE J. Solid-State Circuits, vol. 29, no. 12, pp. 1505-1513, Dec. 1994. https://doi.org/10.1109/4.340424
  14. Y.-J. Kim, H.-C. Choi, G.-C. Ahn, and S.-H. Lee, "A 12b 50 MS/s CMOS Nyquist A/D converter with a fully differential class-AB switched op-amp," IEEE J. Solid-State Circuits, vol. 45, no. 3, pp. 620-628, Mar. 2010. https://doi.org/10.1109/JSSC.2009.2039534
  15. C. D. Kim, J. Y. Han, Y. W. Kim, N. J. Song, M. W. Ha, S. H. Lee, "A 1280-RGB x 800-Dot Driver based on 1:12 MUX for 16M-Color LTPS TFT-LCD Displays," Journal of the Institute of Electronics and Information Engineers, vol. 46, SD, no. 1, pp. 98-106, Jan. 2009.
  16. H.-S. Kim, J.-H. Yang, S.-H. Park, S.-T. Ryu, and G.-H. Cho, "A 10-Bit Column-Driver IC With Parasitic-Insensitive Iterative Charge-Sharing Based Capacitor-String Interpolation for Mobile Active-Matrix LCDs," IEEE J. Solid-State Circuits, vol. 49, no. 3, pp. 766-782, Mar. 2014. https://doi.org/10.1109/JSSC.2014.2302301