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.