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A capacitive DAC with custom 3-D 1-fF MOM unit capacitors optimized for fast-settling routing in high speed SAR ADCs

Chixiao Chen, Jixuan Xiang, Huabin Chen, Jun Xu, Fan Ye, Ning Li and Junyan Ren

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 Corresponding author: Junyan Ren, E-mail: jyren@fudan.edu.cn

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Abstract: Asynchronous successive approximation register (SAR) analog-to-digital converters (ADC) feature high energy efficiency but medium performance. From the point of view of speed, the key bottleneck is the unit capacitor size. In this paper, a small size three-dimensional (3-D) metal-oxide-metal (MOM) capacitor is proposed. The unit capacitor has a capacitance of 1-fF. It shapes as an umbrella, which is designed for fast settling consideration. A comparison among the proposed capacitor with other 3-D MOM capacitors is also given in the paper. To demonstrate the effectiveness of the MOM capacitor, a 6-b capacitive DAC is implemented in TSMC 1P9M 65 nm LP CMOS technology. The DAC consumes a power dissipation of 0.16 mW at the rate of 100 MS/s, excluding a source-follower based output buffer. Static measurement result shows that INL is less than ± 1 LSB and DNL is less than ± 0.5 LSB. In addition, a 100 MS/s 9-bit SAR ADC with the proposed 3-D capacitor is simulated.

Key words: metal-oxide-metal capacitorSAR analog-to-digital convertorsdigital-to-analog convertors



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Fig. 1.  MOM capacitors for SAR ADCs. (a) A general model for unit MOM capacitor. (b-d) 3-D MOM capacitor from References [2, 4, 5], respectively.

Fig. 2.  Multi-view on the proposed 3-D MOM capacitor.

Fig. 3.  A 3-D illustration on the proposed custom MOM capacitor.

Fig. 4.  Circuit implementation of the test chip.

Fig. 5.  Die photo and detailed layout diagram.

Fig. 6.  Static measurement result including INL and DNL.

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Table 1.   Comparison of the 3-D MOM Capacitors with same area and process.

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    Received: 09 September 2014 Revised: Online: Published: 01 May 2015

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      Chixiao Chen, Jixuan Xiang, Huabin Chen, Jun Xu, Fan Ye, Ning Li, Junyan Ren. A capacitive DAC with custom 3-D 1-fF MOM unit capacitors optimized for fast-settling routing in high speed SAR ADCs[J]. Journal of Semiconductors, 2015, 36(5): 055011. doi: 10.1088/1674-4926/36/5/055011 C X Chen, J X Xiang, H B Chen, J Xu, F Ye, N Li, J Y Ren. A capacitive DAC with custom 3-D 1-fF MOM unit capacitors optimized for fast-settling routing in high speed SAR ADCs[J]. J. Semicond., 2015, 36(5): 055011. doi: 10.1088/1674-4926/36/5/055011.Export: BibTex EndNote
      Citation:
      Chixiao Chen, Jixuan Xiang, Huabin Chen, Jun Xu, Fan Ye, Ning Li, Junyan Ren. A capacitive DAC with custom 3-D 1-fF MOM unit capacitors optimized for fast-settling routing in high speed SAR ADCs[J]. Journal of Semiconductors, 2015, 36(5): 055011. doi: 10.1088/1674-4926/36/5/055011

      C X Chen, J X Xiang, H B Chen, J Xu, F Ye, N Li, J Y Ren. A capacitive DAC with custom 3-D 1-fF MOM unit capacitors optimized for fast-settling routing in high speed SAR ADCs[J]. J. Semicond., 2015, 36(5): 055011. doi: 10.1088/1674-4926/36/5/055011.
      Export: BibTex EndNote

      A capacitive DAC with custom 3-D 1-fF MOM unit capacitors optimized for fast-settling routing in high speed SAR ADCs

      doi: 10.1088/1674-4926/36/5/055011
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      • Corresponding author: E-mail: jyren@fudan.edu.cn
      • Received Date: 2014-09-09
      • Accepted Date: 2014-10-23
      • Published Date: 2015-01-25

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