Peter R. Holloway

Comparator-based switched-capacitor circuits for scaled CMOS technologies

A comparator-based switched-capacitor circuit (CBSC) technique is presented for the design of analog and mixed-signal circuits in scaled CMOS technologies. The technique involves replacing the operational amplifier in a standard switched-capacitor circuit with a comparator and a current source. During charge transfer, the comparator detects the virtual ground condition in place of the opamp which normally forces the virtual ground condition. A prototype 1.5-bit/stage 10-bit 7.9-MS/s pipeline ADC was designed using the comparator-based switched-capacitor technique. The prototype ADC was implemented in 0.18-mum CMOS. It achieves an ENOB of 8.6 bits for a 3.8-MHz input signal and dissipates 2.5 mW

Comparator-Based Switched-Capacitor Circuits for Scaled CMOS Technologies

A comparator-based switched-capacitor (CBSC) design method for sampled-data systems utilizes topologies similar to traditional opamp-based methods but relies on the detection of the virtual ground using a comparator instead of forcing it with feedback. A prototype 10b CBSC 1.5b/stage pipelined ADC is implemented in a 0.18mum CMOS process. The converter operates at 8MHz and consumes 2.5mW

Noise Analysis for Comparator-Based Circuits

Noise analysis for comparator-based circuits is presented. The goal is to gain insight into the different sources of noise in these circuits for design purposes. After the general analysis techniques are established, they are applied to different noise sources in the comparator-based switched-capacitor pipeline analog-to-digital converter (ADC). The results show that the noise from the virtual ground threshold detection comparator dominates the overall ADC noise performance. The noise from the charging current can also be significant, depending on the size of the capacitors used, but the contribution was small in the prototype. The other noise sources have contributions comparable to those in op-amp-based designs, and their effects can be managed through appropriate design. In the prototype, folded flicker noise was found to be a significant contributor to the broadband noise because the flicker noise of the comparator extends beyond the Nyquist rate of the converter.