Switched-Capacitor CTAT Circuit for Low-Power Bandgap Biasing
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Solution Overview
Problem
Conventional CTAT circuits for low-power bandgap operations require high-resistance resistors, occupying large chip areas and consuming high current, while existing alternatives are not reliable in specified operation conditions.
Innovation Solution
A CTAT circuit using a switched capacitor voltage divider and a voltage-to-current converter to scale down the CTAT voltage and current, reducing resistor area and current consumption by using passive components and low-power active blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a high-resistance resistor is used to achieve very low CTAT currents for low-power operations, then current consumption is reduced, but the resistor occupies a large chip area
Solution Approach 1:
The circuit is divided into two functional blocks: a CTAT current generator and a voltage divider. The voltage divider is further segmented into switched capacitor-based stages, allowing the resistor to operate at higher current while the final output current is reduced through sequential voltage division, thus reducing the required resistor area
Solution Approach 2:
Switched capacitors are introduced as intermediary elements between the CTAT current generator and the resistor. These capacitors store and transfer charge to create scaled-down voltage versions, enabling the resistor to work at optimized current levels while achieving the desired low output current through the intermediary charging/discharging process
2Device complexity
If a conventional resistor-based CTAT circuit is used, then the circuit is simple in structure, but it occupies large chip area and consumes high current for low-power operations
Solution Approach 1:
The conventional purely resistive voltage division is replaced with a switched capacitor-based voltage division system. This substitution uses electrical charge storage and transfer mechanisms instead of relying solely on resistive ratios, enabling compact implementation with reduced area while maintaining the essential voltage division function
Solution Approach 2:
The switched capacitor voltage divider operates through periodic switching cycles, where capacitors are alternately charged and discharged to achieve voltage division. This periodic operation allows the circuit to achieve low output current through time-averaged charge transfer rather than requiring a continuously high-resistance path
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 effectively reduces CTAT current and resistor area, achieving a more compact and low-power circuit suitable for low-power bandgap operations.
Implementation Method 1
a switched capacitor voltage divider connected to the diode and configured to receive the forward voltage and to output a scaled voltage that is a fraction of the forward voltage
Implementation Method 2
a voltage-to-current converter coupled between the switched capacitor voltage divider and the resistor and that is configured to provide a resistor current, which is proportional to the scaled voltage and inversely proportional to a resistance of the resistor
Implementation Method 3
The diode is configured to receive a diode current so that a forward voltage occurs across the diode
Data Source
AI summary
In accordance with an embodiment, a circuit includes: a switched-capacitor voltage divider; a voltage-to-current converter coupled to an output of the switched-capacitor voltage divider, wherein a first output node of the voltage-to-current converter is configured to provide a CTAT current with respect to a reference resistance; a current mirror having an input coupled to a second output node of the voltage-to-current converter, and a diode junction coupled to an output of the current mirror and to an input of the switched-capacitor voltage divider.