Supply-Selection Circuit for IC Body-Bias Control
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Solution Overview
Problem
Conventional supply-switching circuits for integrated circuits often select the battery when the main supply voltage is within a predetermined range, leading to inefficient power management and reduced battery life due to diode drops and unnecessary switching, as well as increased production costs from additional electronic components.
Innovation Solution
A supply-selection system utilizing first through third transistors with specific connections and a control logic circuit that ensures the main supply is selected when within a predetermined range and switches to the battery only when the main supply is unavailable, eliminating diode drops and reducing battery leakage by avoiding fixed-current sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diode is used in the switching circuit to prevent battery leakage, then battery protection is improved, but voltage is reduced due to diode drop
Solution Approach 1:
The patent removes the diode from the switching circuit entirely. Instead of using a diode to prevent battery leakage, the invention uses a PMOS transistor with its body terminal connected to a higher voltage source, which inherently prevents the body diode from conducting and thus eliminates battery leakage without introducing voltage drop.
Solution Approach 2:
The patent introduces a higher voltage source (VHIGH) as an intermediary to control the body terminal of the PMOS transistor. This intermediary voltage ensures that the body diode remains reverse-biased and does not conduct, preventing battery leakage without the need for a series diode that would cause voltage drop.
2Reliability
If additional electronic components are added to the supply-switching circuit, then switching control is improved, but production cost and chip area increase
Solution Approach 1:
The PMOS transistor in the patent serves multiple functions simultaneously: it acts as the switching element, provides body-bias voltage control through its body terminal connection, and prevents battery leakage through its body diode configuration. This multi-functionality eliminates the need for separate diodes and reduces overall circuit complexity.
Solution Approach 2:
The patent combines the switching function and the body-bias control function into a single PMOS transistor structure. The body terminal connection to VHIGH merges the protection function with the switching function, eliminating the need for separate protective components and reducing chip area.
3Reliability
If the battery is selected when main supply voltage is within predetermined range, then power redundancy is improved, but battery life is reduced due to unnecessary switching
Solution Approach 1:
The patent implements voltage monitoring that provides feedback to the switching control. The circuit monitors the main supply voltage and only switches to battery power when the main supply voltage falls outside the predetermined range, preventing unnecessary battery discharge and extending battery life while maintaining power redundancy when needed.
Data Source
AI summary
A system for providing a first voltage generated by a main supply and a second voltage generated by a battery to an integrated circuit (IC) includes supply-selection, control logic and switching circuits. The supply-selection circuit includes first, second, and third transistors. The switching circuit includes fourth and fifth transistors that supply the first and second voltages to the IC when switched on. The supply-selection circuit selects and provides the higher of the first and second voltages to body terminals of the fourth and fifth transistors for maintaining required body-bias voltage conditions. The control logic circuit generates a first control signal as long as the first voltage is within a predetermined range for keeping the fourth transistor switched on and a second control signal when the first voltage is not within the predetermined range for switching on the fifth transistor to supply the second voltage.