A Charge-Sharing-Based Two-Phase Charging Scheme for Zero-Crossing-Based Integrator Circuits

Abstract

As an effort to improve the energy efficiency of switched-capacitor circuits, zero-crossingbased integrators (ZCBI) that consist of zero-crossing detectors and charging circuits have been proposed. To break the trade-off between accuracy and speed, ZCBI typically employs a two-phase charging scheme that relies on an additional threshold for zero-crossing detection. This paper proposes a simpler realization method of the two-phase charging scheme by means of charge sharing. To demonstrate feasibility of the proposed method, we designed and fabricated a second-order delta-sigma modulator in 180-nm complementary metal-oxide-semiconductor (CMOS) technology. The measurement results show that the modulator exhibits a peak signal-to-noise-and-distortion ratio (SNDR) of 46.3 dB over the bandwidth of 156 kHz with the power consumption of 684 µW. We also designed the same modulator in 65-nm CMOS technology and simulation results imply that the proposed circuit is able to achieve a much better energy efficiency in advanced technology.

A Zero-Crossing-Based Integrator with Bidirectional Two-Phase Charging and Selective-Reset Operations for ΔΣ ADCs

“…Consequently, the signal-dependent overshoot error results in increased harmonic distortions. The amount of overshoot can be reduced without sacrificing the speed too much by employing twophase (coarse and fine) charging schemes [9], [10]. During the coarse phase, the charging current level is high for speed; during the fine phase, the charging current level is low for lower overshoot.…”

“…Furthermore, the additional threshold should be well controlled under process-voltagetemperature (PVT) variations. [10] implemented a two-phase charging scheme by means of simple charge sharing, but its usefulness might be marginal under severe PVT variations as well. The implementations in [9], [10] are able to reduce the amount of overshoot but the errors are still signal-dependent.…”

“…We simulated the total harmonic distortions (THDs) of integrators with three different twophase charging schemes: the proposed bidirectional scheme, charge-sharing scheme (Fig. 4(a) [10]), and the unidirectional scheme (Fig. 4(b) [11]).…”

“…This paper proposes an inverter-based ZCBI with a two-phase charging scheme that is simple to implement and also creates less signal-dependent overshoot errors. In general, ZCBIs exhibit lower static power consumption than conventional SC circuits, especially when the ZCD is implemented using a digital inverter with an auto-zeroed capacitor [9], [10]. The inherent reset operation in ZCBI circuits, however, may increase the dynamic power consumption.…”

A Novel Offset and Finite-Gain Compensated Switched-Capacitor Amplifier with Input Correlated Level Shifting

“…Recently, several techniques have been developed to alleviate the finite gain error of op-amps in SC circuits, such as comparator-based SC (CBSC) circuits [11,12], digital circuits-based SC circuits, which are also called zero-crossing-detectors-based (ZCD) SC circuits [13][14][15] and digital calibration algorithms [16][17][18]. However, CBSC circuits introduce large offset errors and linearity problems due to the output overshoots and voltage drop on switches [19].…”