Switched Capacitor Voltage Divider Leakage Reduction
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Solution Overview
Problem
Conventional voltage dividers in integrated circuits suffer from significant leakage due to reverse biased and channel leakage mechanisms, which introduce nondeterministic errors and are challenging to calibrate, especially in high precision sampled systems.
Innovation Solution
A switched capacitor divider architecture is implemented with a pair of capacitors and switches that enable charge sharing between them, minimizing leakage by providing a high impedance connection to the discharge switch and reducing the bulk voltage of the sampling switch to match the output voltage, thereby reducing reverse biased and channel leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional switched capacitor divider is used to step down DC voltages in sampled systems, then voltage division can be achieved, but significant leakage occurs through reverse biased and channel leakage mechanisms
Solution Approach 1:
The voltage divider is segmented into multiple phases (first phase for charging, second phase for discharge, third phase for charge sharing) with dedicated switches for each function. This segmentation allows the discharge switch to be isolated from the sampling capacitor during charging, eliminating channel leakage, and enables separate optimization of each phase's switching elements.
Solution Approach 2:
The bulk voltage of the sampling switch is preliminarily set to match the output voltage level before the charging phase begins. This preliminary voltage matching prevents reverse biased leakage through the source-to-bulk and drain-to-bulk diodes during the charging phase, as there is no voltage difference to drive the leakage current.
Solution Approach 3:
A dedicated charge sharing switch is introduced as an intermediary element to transfer charge between the sampling capacitor and the output capacitor. This intermediary switch isolates the main discharge switch from direct connection to the sampling capacitor, eliminating the channel leakage path while still enabling the voltage division function through controlled charge transfer.
2Device complexity
If a resistor divider is used to step down DC voltages, then simple voltage division is achieved, but temperature coefficient and poor supply rejection introduce errors
Solution Approach 1:
The passive resistor divider is replaced with an active switched capacitor system that uses capacitors and controlled switches instead of resistors. This substitution eliminates the temperature-dependent resistance values and supply rejection issues inherent in resistor dividers, as capacitors have much lower temperature coefficients and the switched capacitor architecture provides inherent supply rejection through synchronous switching.
Solution Approach 2:
The invention changes the fundamental operating parameters from continuous DC voltage division through resistors to phased charge transfer through capacitors. By operating in discrete phases with controlled switching, the system achieves voltage division based on capacitor ratios rather than resistor ratios, providing superior temperature stability and supply rejection while maintaining the voltage division function.
3Reliability
If conventional voltage dividers are used in high precision sampled systems, then voltage stepping is achieved, but nondeterministic leakage errors cannot be calibrated out
Solution Approach 1:
The discharge function is extracted from the main sampling path and implemented as a separate phase with dedicated switches. The discharge switch operates only during the second phase when the sampling capacitor is disconnected from the input, eliminating channel leakage during the critical charging phase. This extraction makes the leakage paths deterministic and phase-dependent, allowing for calibration if needed.
Solution Approach 2:
The voltage division function continues uninterrupted through the phased operation. During the first phase, the sampling capacitor charges to the input voltage. During the second phase, it discharges to the output node. During the third phase, charge sharing occurs. This continuous phased operation ensures that voltage division is maintained throughout the sampling cycle without gaps, while leakage is confined to specific phases where it can be managed or calibrated.
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
This approach reduces leakage by over two orders of magnitude compared to conventional voltage dividers, enhancing the reliability and enabling a more area-efficient capacitor structure, suitable across various process, voltage, and temperature conditions.
Implementation Method 1
a bypass switch having a first terminal coupled to the first terminal of the second capacitor and a second terminal coupled to the second terminal of the second capacitor; and a charge sharing switch coupled to the second terminal of the second capacitor; wherein the bypass switch and the charge sharing switch enable the sharing of charge between the first capacitor and the second capacitor
Implementation Method 2
minimizing leakage by providing a high impedance connection to the discharge switch
Implementation Method 3
Dominant leakage mechanisms include reverse biased leakage through the source-to-bulk (S/B) or the drain-to-bulk (D/B) diodes
Implementation Method 4
channel leakage through the discharge switch (which results in leakage off the sampling capacitor)
Data Source
AI summary
A voltage divider is described. The voltage divider comprises a pair of input nodes for receiving an input signal; a pair of output nodes configured to generate an output signal; a first capacitor having a first terminal coupled to a first output node of the pair of output nodes and a second terminal coupled to a second output node of the pair of output nodes; and a second capacitor having first terminal and a second terminal; a bypass switch having a first terminal coupled to the first terminal of the second capacitor and a second terminal coupled to the second terminal of the second capacitor; and a charge sharing switch coupled to the second terminal of the second capacitor; wherein the bypass switch and the charge sharing switch enable the sharing of charge between the first capacitor and the second capacitor.