Reconfigurable Opamp-Free Delta-Sigma SAR ADC
Computing & Wireless : Hardware
Available for licensing
- Nan Sun, Ph.D. , Electrical & Computer Engineering
- Wenjuan Guo , University of Texas at Austin
Nowadays successive approximation-register (SAR) analog-to-digital converters (ADCs) are very popular with the ADC market, due to their power efficiency and compatibility with the technology. However, all the building blocks of an SAR, including the sample-and-hold (S/H) circuit, the DAC, and the comparator, are required to be as accurate as the overall ADC system, thus limiting their resolution to the medium range (8-12 bits). In contrast, delta-sigma ADCs trade speed for resolution, becoming the main choice for modern high-precision applications.
Through oversampling and noise shaping, delta-sigma ADCs greatly relax the accuracy requirement of many blocks. Their disadvantage is that the use of active integrators increases power consumption and design complexity. Realizing delta-sigma using SAR architectures is a power-efficient and hardware-friendly method for high-resolution ADCs. The reduction in power and hardware cost also benefits the ADC market by reducing production cost.
The delta-sigma SAR ADC combines the advantages of both SAR ADCs and delta-sigma ADCs, providing a low-power and low-cost architecture for high-resolution ADCs. Due to the inherent properties of the SAR ADC, simple passive integrators are designed to replace the active integrators in conventional delta-sigma ADCs. The proposed architecture can also be easily reconfigured according to the noise shaping order requirement. To prove the proposed concept, a delta-sigma SAR ADC capable of operating in three working modes--no noise shaping, first-order noise shaping, and second-order noise shaping--was created using CMOS technology.
The realization of delta-sigma on SAR architectures makes it possible to design a high-resolution ADC with minimum power consumption and design efforts.
- Reduces power compared to conventional delta-sigma ADCs
- Increases resolution compared to conventional SAR ADCs
ADCs are widely used in modern mixed-signal integrated-circuit (IC) industry. SAR ADCs are the choice of low-power ADCs in applications such as portable/battery-powered instruments, pen digitizers, industrial controls, and data/signal acquisition. Delta-sigma ADCs are the choice of high-resolution ADCs in applications such as modern voice-band, audio, and precision industrial control/measurement. The delta-sigma ADCs have the potential to replace conventional SAR ADCs and delta-sigma ADCs in their corresponding applications.