Comparison of Opamp-Based and Comparator-Based Delta-Sigma Modulation

Abstract

Comparator-based switched capacitor (CBSC) circuits present an alternative approach to designing sampled data systems based on the principle of detecting a virtual ground condition with a comparator rather than actively enforcing it with a high-gain operational amplifier (opamp) in feedback. This work demonstrates a 2 nd -order ∆Σ converter designed using the CBSC technique. The same modulator topology was also implemented using two conventional design methods for a two-stage Miller-compensated amplifier and a single-stage folded cascode amplifier, such that all three blocks can be used as 'drop-in replacements' in the top-level circuit. The designs are done in a 0.13 µm UMC technology. The SNDR performance and power consumption of all three approaches were simulated with a sampling frequency of 5.12 MHz and an oversampling ratio of 64. It can be concluded that the CBSC method provides a great simplification of design effort and significant power savings compared to the traditional OTA-based methods.

Realization of DVCCTA Based Versatile Modulator

“…Implementation scheme Active element used Modulation type [1] Schmitt trigger followed by integrator CCII, Opamps PWM [2,3] Schmitt trigger followed by integrator OTAs PWM [4] Schmitt trigger followed by integrator OTAs AM, FM, delta, and sigma delta [5] Schmitt trigger followed by integrator CCCDTA PWM [6] Schmitt trigger followed by integrator MOCCCDTA PWM [7] Schmitt trigger followed by integrator OTRA PWM [8] Switched capacitor Opamps Sigma delta [9] Comparator based switched capacitors Dynamic Comparator OTA Sigma delta [10] Class-C inverter switched capacitor Class-C inverter Sigma delta [11] Comparator based switched capacitors Opamps Sigma delta [12] Switched current CMOS None Sigma delta [13][14][15] Loop filter + quantizer Opamps Sigma delta Proposed Schmitt trigger followed by integrator DVCCTA AM, FM, delta, and sigma delta…”

“…The pulse width of the carrier signal is modulated in accordance with input modulating signal in circuits proposed in [1][2][3][4][5][6][7]. Sigma delta modulators are the other class of modulators available in literature [4,[8][9][10][11][12][13][14][15]. These modulators can be classified as designs based on (i) switched capacitor technique [8][9][10][11], (ii) switched current technique [12], (iii) Loop filter and quantizer method [13][14][15], and (iv) ABB [4].…”

“…Sigma delta modulators are the other class of modulators available in literature [4,[8][9][10][11][12][13][14][15]. These modulators can be classified as designs based on (i) switched capacitor technique [8][9][10][11], (ii) switched current technique [12], (iii) Loop filter and quantizer method [13][14][15], and (iv) ABB [4]. A detailed comparison of these structures is given in Table 1.…”