Charge Pump Adaptive Dead-Time and Body Biasing
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Solution Overview
Problem
Conventional charge pumping apparatuses face inefficiencies at low input voltages due to high leakage current and poor power conversion efficiency, particularly in designs using forward body biasing and cross-coupled NMOS transistors.
Innovation Solution
A charge pump circuit with a negative charge pump, adaptive dead-time circuit, and switching body biasing technique is implemented, utilizing a series of unit charge pumps with PMOS switches for body biasing and an adaptive dead-time circuit that selects between short and long dead-times based on input voltage, minimizing reverse current and maximizing power transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If forward body biasing (FBB) technique is used to improve voltage conversion efficiency for low input voltages, then voltage conversion efficiency is improved, but power conversion efficiency deteriorates
Solution Approach 1:
The patent implements dynamic body biasing that switches between forward body biasing and reverse body biasing based on operating conditions. During the off-state of switches, reverse body biasing is applied to minimize leakage current, while forward body biasing is applied during on-state to maintain low threshold voltage. This dynamic switching resolves the contradiction by optimizing for voltage conversion efficiency during charging phases and power efficiency during discharge phases.
Solution Approach 2:
The patent employs periodic switching of body biasing polarity synchronized with the charge pump operation cycles. The body biasing voltage alternates between forward and reverse biasing in periodic fashion, matching the switching frequency of the charge pump stages. This periodic action ensures that FBB benefits are realized during active charging intervals while RBB benefits are realized during discharge intervals, resolving the efficiency contradiction.
2Power
If NMOS switches are used with forward body biasing to achieve higher current transfer, then current transfer is improved, but leakage current increases
Solution Approach 1:
The patent dynamically switches the body biasing voltage of NMOS switches between forward and reverse biasing based on their operational state. When switches are in the on-state, forward body biasing reduces threshold voltage to maximize current transfer capability. When switches transition to off-state, reverse body biasing is applied to increase threshold voltage and minimize subthreshold leakage current. This dynamic adaptation resolves the contradiction between current transfer and leakage reduction.
Solution Approach 2:
The patent uses body biasing voltage as a control mechanism analogous to hydraulic pressure control. By adjusting the body biasing voltage polarity and magnitude, the patent effectively controls the 'pressure' (threshold voltage) of the NMOS switches to optimize flow (current) in different operational phases, resolving the contradiction between high current transfer and low leakage.
3Loss of energy
If reverse body biasing (RBB) is applied to minimize leakage current, then leakage current is reduced, but NMOS switches cannot be turned on at low input voltages
Solution Approach 1:
The patent implements dynamic body biasing control where the body biasing voltage is adjusted in real-time based on the operational requirements. During off-state, reverse body biasing is applied to minimize leakage current. During on-state transitions, forward body biasing is applied to ensure adequate threshold voltage reduction for reliable switch turn-on, even at low input voltages. This dynamic adaptation resolves the contradiction between leakage reduction and switch activation capability.
Solution Approach 2:
The patent applies forward body biasing in advance before the switching operation to prepare the NMOS switches for low-voltage turn-on. By pre-applying forward body biasing during the on-state phase, the threshold voltage is reduced beforehand, ensuring that switches can be reliably turned on even when input voltages are low. This preliminary action resolves the contradiction by ensuring switch activation capability is maintained while allowing reverse body biasing to be applied during off-state for leakage reduction.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly improves power conversion efficiency at low input voltages, extending the operating range below ground and maintaining efficiency at both low and high voltage operations, with measured improvements in output current and power throughput compared to conventional designs.
Implementation Method 1
Each unit charge pump includes: a first pumping capacitor, a second pumping capacitor, two cross-coupled NMOS switches, wherein the first pumping capacitor is coupled to the source of a first cross-coupled NMOS switch and the gate of the second cross-coupled NMOS switch
Implementation Method 2
The conventional CP-cross can be improved by using a bulk switching (BS) technique... the use of NMOS is a better choice than using PMOS because of higher mobility. The BS technique keeps the body of the PMOS switches at the highest voltage, even though the load current is heavy so that the voltage drop at the output is large, which avoids degradation of the threshold voltage due to the body effect
Data Source
AI summary
A charge pump (CP) that operates at low input voltage with high power conversion efficiency is disclosed. A first embodiment provides a negative CP used for controlling load switches of a voltage doubler. Using a negative CP extends the operating region below ground to relieve the power delivery limitation of the CP. A second embodiment provides a low power adaptive dead-time circuit, which has several dead-time signals having different lengths of dead-times and selects one according to the input voltage level. A low input voltage detector in the adaptive dead-time circuit is used to determine which dead-time should be used. A third embodiment provides a switching body bias used for the low input voltage CP. The switching body bias uses both forward and reverse body bias applied to the CP to minimize reverse current and maximize power transfer. The first, second, and third embodiments can be used together or independently.