| Status | 已發表Published |
| Title | Digital Assisted Techniques for Bridge DAC Capacitor Mismatch Calibration in SAR ADC |
| Author | Wang , G.C.; Zhu, Y.  ; Chan, C. H.; U, S.P.
|
| Date Issued | 2017-08-31 |
| Keyword | Bridge DAC Capacitor Mismatch Calibration SAR ADC |
| Abstract | Analog to digital converter (ADC) is widely used in our life as the interface of the analog world and the digital world. The development and population of portable device (for example, the smartphone and tablet computer) create huge demand of high performance ADCs with low power consumption and small area. Successive-approximation-register (SAR) ADC is one of the popular architectures that provides properly resolution and speed with high power efficiency. It mainly consists of a capacitor digital-to-analog converter (CDAC), a comparator and SAR control logic. CDAC is the essential component that determines the conversion linearity of ADC. Bridge-DAC is the prevalent architecture of DAC that divides the DAC into the most significant bit (MSB) array and the least significant bit (LSB) array with an attenuation capacitor. It can significantly reduce the total unit capacitor and save area. However, the mismatch of the non-unit attenuation capacitor and the parasitic capacitor may cause gain error between the MSB array and the LSB array. Thanks to the downscaling of complementary metal oxide semiconductor (CMOS) technology, digital-assisted calibrations are proposed and implemented in ADCs. This thesis proposes two digital-assisted calibration for the gain error caused by the bridge digital-to-analog converter (DAC) mismatch. One is the missing code detection calibration (MCD) in digital domain while other is the feedback missing code detection (FMCD) calibration in analog domain. Both algorithms estimate the gain error by detecting the occurrence of missing codes. To eliminate the calibration dependence to the input signal, a testing signal generator(TSG) is proposed whose the circuit implementation and design consideration are introduced in detail. The MCD algorithm replaces the gain factor calculation with simple missing-codes count that significantly reduces the calibration digital overhead. The concept was verified in an 80MS/s 11bit SAR with DAC. Besides, the comparisons between the proposed and the code-statistic based scheme in terms of the accuracy and hardware complexities are discussed. The analysis is based on mathematic model with behavior simulation verifications. The measurement results demonstrate that the signal-to-noise ratio (SNR) can be improved by 7.4dB from 55.7dB to 63dB at DC input frequency. The FMCD calibration estimates the DAC mismatch by detecting the missing coed rather than comparing the DAC outputs with certain condition that simplifies the circuit implementation. The accuracy of the calibration and design consideration is introduced. Besides, its effectiveness is verified by behaviors simulations and measurement results. This conception is implemented in a 100MS/s 12-bit SAR ADC with bridge DAC. The measurement results depict that the SNR is improved from 61dB to 64dB at direct current (DC) input frequency and the missing codes caused by DAC mismatch are all removed without losing the dynamic rang. |
| Language | 英語English |
| PUB ID | 38600 |
| Document Type | Thesis |
| Collection | INSTITUTE OF MICROELECTRONICS |
| Corresponding Author | Zhu, Y. |
| Recommended Citation GB/T 7714 | Wang , G.C.,Zhu, Y.,Chan, C. H.,et al. Digital Assisted Techniques for Bridge DAC Capacitor Mismatch Calibration in SAR ADC[D], 2017. |
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