Low-Power Voltage Detector Using Diode Ladder for CMOS
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Solution Overview
Problem
Existing battery-voltage detectors may damage sensitive semiconductor devices during power-down mode due to fluctuations in battery voltage, and they fail to accurately measure battery voltage due to variations in diode voltage drops caused by process, voltage, and temperature (PVT) conditions.
Innovation Solution
A battery-voltage detector that measures voltages at both terminals of a diode ladder, multiplying the measured diode voltage drop by the number of diodes to estimate the battery voltage, while using a resistor and switch configuration to limit current and power consumption, and employing a buffered or transistor-switched design to protect sensitive components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a power-down switch is opened to reduce power consumption, then power consumption is reduced, but voltage spikes can damage sensitive transistors
Solution Approach 1:
A diode is introduced as an intermediary component between the voltage detector output and the sensitive transistor. The diode's forward voltage drop (typically 0.7V) acts as a natural voltage limiter, ensuring that even when the power-down switch opens and voltage spikes occur, the sensitive transistor never experiences voltage above VBAT - Vdiode. This mediator protects the transistor without requiring active control or additional switching complexity.
2Object-affected harmful factors
If diodes are used to prevent voltage spikes, then transistor protection is improved, but measurement precision deteriorates due to PVT variations
Solution Approach 1:
The invention changes the measurement approach from directly measuring voltage at a fixed point to measuring the voltage drop across the protective diode itself. By measuring Vdiode = VDET0 - VDET1 (the voltage difference between the two diode terminals), the system captures a parameter that is relatively stable across PVT conditions. Since the diode and transistor are fabricated together, they experience correlated variations, making the diode voltage drop a reliable reference for accurate battery voltage measurement.
3Use of energy by moving object
If advanced semiconductor processes are used to reduce power consumption, then power consumption is reduced, but sensitivity to voltage damage increases
Solution Approach 1:
The protective diode is permanently integrated into the voltage detector circuit before the power-down switch can potentially cause voltage spikes. This beforehand cushioning ensures that sensitive transistors in advanced CMOS processes are always protected, regardless of the switch state. The diode's inherent voltage drop creates a safety margin that accommodates the higher voltage sensitivity of advanced process transistors while allowing the use of low-power design techniques.
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 protects sensitive devices from damage during power-down mode and provides accurate battery voltage measurement by ensuring consistent diode voltage drops across all diodes, reducing power consumption and preventing voltage spikes.
Implementation Method 1
current flowing through each of diodes 30, 32, 34, 36 causes a pn-junction voltage drop Vpn of about 0.5-0.7 volt per diode
Implementation Method 2
A current-limiting resistor 40 is connected in series with the diode ladder
Data Source
AI summary
A voltage detector has a diode ladder with one or more diodes connected in series between a battery voltage input and an upper measuring node. A measuring diode is connected between the upper measuring node and a lower measuring node. A resistor and a power-down switch are connected in series between the lower measuring node and a ground. An analog input to an Analog-to-Digital Converter (ADC) is connected by a switch to the upper measuring node to generate an upper digital value. Then the switch connects the analog input to the lower measuring node to generate a lower digital value. The difference between the upper and lower digital values is the diode voltage drop across the measuring diode and is multiplied by a number of diodes in the diode ladder and added to the upper digital value to generate a battery voltage measurement.