Design and Verification of An Energy-Efficient Edge-Pursuit Comparator

Sammanfattning: With the rapid development of mobile communication, sensors, and biomedical in recent years, the demand for accurate data information, highquality audio and image has become much more significant, which requires a high-precision Analog to Digital Converter (ADC) to process weak analog signals. As one of the core modules of ADC, the comparator’s precision, speed, stability, and noise play a key role in the performance of the whole circuit. Over the years, those performance has been improved a lot by both designing new architectures and using advanced fabrication technology. However, the conventional comparators occupy 50%-60% of the total energy consumption of EPC, even with advanced technology and lower supply voltage. In this thesis, a new type of energy-efficient comparator, called Edge-Pursuit Comparator (EPC), is proposed, which satisfies the need for low comparison energy. The design of EPC is based on a ring oscillator, when the EPC enters the evaluation mode, two signal edges with different propagation delays will chase in it until one overlaps the other, and finally generate a stable voltage level in each output node. The circuit is built and simulated in Cadence Virtuoso using cmos22fdsoi technology. The simulation results reveal that the energy consumed per comparison is dependent on the input differential voltage, and it can be as low as 7 fJ when vin = 50 mV, which is around ten times smaller compared with conventional comparators. In addition, as the power consumption is considerable when the two input voltages are very close, a promising improvement is applied to EPC, namely connecting every node with a variable capacitor, which is called Edge-Pursuit Comparator enhanced with Capacitor (EPCC). Cadence simulation results prove that EPCC can largely lower the energy consumption under a small vin while keeping input-referred noise the same. Therefore, a combination of EPC and EPCC is expected to have prospective applications in the energy-efficient area.