Fig.5 Simulated spectrum.
Fig.6 Noise and power breakdown.
(a)
(b)
Fig.7 Simulation results of the sampling circuits in (a) traditional SAR ADC and (b) proposed SAR ADC
Fig. 7 compares the simulated voltage and current waveforms of the sampling circuits in a conventional SAR ADC and the proposed one. For a conventional SAR ADC, in order to leave as much as time to SAR conversion, typically the tracking phase occupies a small portion of an entire ADC cycle. As shown in Fig. 7(a), 13% of an entire ADC cycle is used for tracking. For a near-Nyquist input signal, the maximum input signal change (ΔVmax) on the sampling capacitor is as high as 990 mV and the peak current (ΔImax) drawn from the input buffer is 44.3 mA. In contrast, for the proposed ADC, the most of an ADC cycle can be allocated for tracking. As shown in Fig. 7(b), 87% of an entire ADC cycle is used for tracking, leading to a short time of disconnection between the input driver and the sampling capacitor. This makes the proposed ADC close to a continuous-time one. Comparing to Fig. 7(a), the maximum input signal change (ΔVmax) on the sampling capacitor and the peak current (ΔImax) are significantly reduced to 256.3 mV and 15.1 mA, respectively. This verifies that the long tracking time can relax the requirement on the driving capability of input buffer.
Conclusion: This work proposes an improved kT/C noise cancellation technique with presampling for SAR ADCs. Comparing to the previous works [4], the proposed technique effectively addresses the nonlinear issues and relaxes the bandwidth requirement of the amplifier, leading to the improved accuracy and reduced power. Comparing to the conventional SAR ADCs, it greatly increases the tracking time and reduces the DAC size, leading to relaxed burden for the input drivers and reference buffers.
Author Contributions: Yuanfan Gu : Data curation; Formal analysis; Validation; Visualization; Methodology;Writing–original draft ;Writing—review & editing. Kaipeng Wang : Formal analysis; Methodology; Validation; Writing–original draft; Writing– review & editing. Tiange Yi : Formal analysis; Validation; Visualization; Writing– review & editing. Xiaoguo Chen : Formal analysis; Validation; Visualization; Writing– review & editing. Shiheng Yang : Formal analysis; Funding acquisition; Methodology. Jiaxin Liu : Conceptualization; Funding acquisition; Project administration; Resources; Supervision; Writing– review & editing.
Acknowledgments: This work was supported by NSFC under Grant 62174023.
Conflict of interest statement: The authors do not have a conflict of interest to disclose.
Data availability statement: The data that support the findings of this study are available from the corresponding author upon reasonable request.