Accurate Current Sensing Circuit Ultra Low Voltage DC-DC Converter
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Solution Overview
Problem
Conventional current sensing circuits in DC-DC converters face challenges such as power wastage due to large sense resistors, non-linearity at low inductor currents, and the need for high supply voltages, which affect accuracy and functionality, especially in high-load and ultra-low voltage applications.
Innovation Solution
The implementation of an integrated circuit with a DC-DC converter that includes an operational amplifier and transistors forming a current mirror, using a negative feedback loop to maintain voltage matching and reduce current offset, allowing accurate and linear current sensing even at low inductor currents and ultra-low voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large sense resistor is used to maintain accuracy and reduce process variation, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent uses a current mirror circuit to create a copy of the inductor current through transistor M2, which then flows through a smaller sense resistor Rsense. This copied current path allows the use of a smaller resistor value while maintaining accurate sensing capability, thereby reducing power consumption in the main current path.
2Use of energy by moving object
If a small sense resistor is used to reduce power consumption, then power efficiency is improved, but measurement precision deteriorates
Solution Approach 1:
The current mirror creates an accurate copy of the inductor current through transistor M2, allowing the use of a smaller sense resistor Rsense in the mirrored path. This maintains measurement precision while reducing the power dissipation in the main current path through the original sense resistor.
3Measurement precision
If bipolar transistors are used to maintain equal voltages for accurate current sensing, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent employs an operational amplifier in a negative feedback configuration to automatically maintain equal voltages at nodes A and B. The op-amp continuously monitors the voltage difference and adjusts transistor M3's conduction to eliminate any imbalance, thereby ensuring accurate current mirroring without requiring complex bipolar transistor voltage matching circuits.
4Reliability
If high supply voltage is used to ensure proper transistor operation, then reliability is improved, but adaptability to ultra-low voltage applications deteriorates
Solution Approach 1:
The patent uses dynamic voltage balancing through the operational amplifier's negative feedback mechanism, which continuously adjusts to maintain proper transistor operation regardless of the supply voltage level. This dynamic adaptation allows the circuit to function reliably across a wide voltage range, from ultra-low voltage applications up to higher voltages, by automatically compensating for voltage variations.
Data Source
AI summary
An integrated circuit includes a DC-DC converter, which includes an inductor; a first transistor coupled to the inductor and configured to pass an inductor current to the inductor; and a second transistor forming a current mirror with the first transistor. The integrated circuit further includes an operational amplifier. The operational amplifier includes a first input node and a second input node. The first input node is configured to couple to a drain of the first transistor when the first transistor is turned on, and decoupled from the drain of the first transistor when the first transistor is turned off. The second input node is coupled to a drain of the second transistor.