A 6-Bit Flash A/D Converter with New Design Techniques

• Main Authors: Chun-Wei Hsu, 許浚偉
• Other Authors: Tai-Haur Kuo
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/j5shzz

碩士 === 國立成功大學 === 電機工程學系碩博士班 === 90 === The thesis presents a high-speed 6-bit CMOS flash ADC with new design techniques. Autozeroing technique without idle time is the most effective way to suppress the errors due to process variation for the applications of continuous input conversion. Interpolation technique can reduce the input loading and the preamplifiers' number efficiently. However, it is difficult to include autozeroing without idle time and interpolation operations in a high-speed low-latency flash ADC at the same time. In this design, New Autozeroing with Interpolation (NAI) technique is proposed to achieve the target. A switching preamplifier is provided in NAI to avoid using non-overlap control signals required by the conventional autozeroing ADCs and to eliminate the interference, caused by the high-speed autozeroing operation, at input nodes. Besides, NAI has the merit of a single-phase control to avoid the synchronous problem since the multi-phase clocks are necessary for recent published flash ADCs with autozero. While charge injection and feedthrough in NAI limit the ADC performance, capacitor averaging technique is incorporated with NAI to decrease these errors. For the use of interpolation approach, large impedance is needed to generate enough interpolation signals to overcome noise and offset errors. That causes a large RC time constant at the interpolation nodes and deteriorates the ADC speed. A technique called, Negative Impedance Compensation (NIC), is presented to solve this problem so that the ADC can thereby achieve a higher conversion rate with small RC time constant. The designed ADC is fabricated in 0.25μm 1P5M CMOS technology and occupies an area of 1.0x0.8 mm^2. The measurement results show that the design can achieve an operating rate of 500MHz with a SNR>30dB. The total chip draws 261mW from 2.5V power supply.