Floating-Rail Reference Circuit Using Dynamic Voltage Tracking
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Solution Overview
Problem
State-of-the-art floating-rail architectures are limited to operating with a minimum battery or DC input voltage of 2.7V, which is higher than the required 1.6V needed for continuous operation in modern semiconductor devices, especially those fabricated at 28 nm and 22 nm technologies, due to the use of 1.8V Gox devices.
Innovation Solution
A low-power floating-rail reference generator that generates a stable floating-rail voltage (VSSHV_REF) using a tracking current source and current scaling resistor, controlled by a differential amplifier, to produce a voltage equal to (VBAT−1.8V) for input voltages between 1.6V and 4.8V, with a total current consumption of less than 100 nano-amperes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional floating-rail architecture is used, then stable 1.8V floating-rail voltage is provided for logic devices, but minimum operating voltage is limited to 2.7V
Solution Approach 1:
The patent implements dynamic voltage tracking by using a differential amplifier to continuously adjust the gate voltages of PMOS transistors based on the input voltage level. This dynamic control enables the floating-rail voltage to adapt to varying input voltages from 1.6V to 4.8V while maintaining the required 1.8V output, resolving the contradiction between stability and adaptability.
Solution Approach 2:
The patent changes the operating parameters of the MOS transistors by adjusting their gate-source voltages dynamically. By controlling the gate voltages of the PMOS transistors through the differential amplifier, the system can operate across a wide input voltage range (1.6V to 4.8V) while maintaining stable output, overcoming the fixed 2.7V minimum limitation of conventional architectures.
2Reliability
If conventional floating-rail architecture with current sink is used, then floating-rail voltage is regulated, but power consumption is high
Solution Approach 1:
The patent removes the conventional current sink circuitry (NMOS transistors 112a and 112b) from the floating-rail architecture. By eliminating this power-consuming component and replacing it with a high-impedance voltage divider and differential amplifier configuration, the system achieves voltage regulation with significantly reduced power consumption, addressing the contradiction between regulation reliability and energy efficiency.
3Ease of manufacture
If 1.8V Gox devices are used for both logic and power transistors, then process compatibility is achieved, but gate-to-source voltage must be limited to 1.8V
Solution Approach 1:
The patent makes the PMOS transistors serve multiple functions: they act as both power switching devices and voltage regulation elements. By using the same 1.8V Gox PMOS transistors for both power control and floating-rail generation, the design achieves process compatibility without requiring separate device types, simplifying the overall architecture while maintaining the required voltage limitations.
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 generator provides a stable floating-rail voltage across logic devices, ensuring they operate within the 1.8V gate oxide limit, while maintaining low power consumption and continuous operation across a wide range of input voltages.
Implementation Method 1
a pair of MOS transistors having a first transistor coupled between the input voltage (VBAT) and the output and a second transistor, and a differential amplifier having an output coupled to gates of the first and second transistors
Implementation Method 2
generate a tracking current (Isource) through the current scaling resistor to produce a floating-rail reference voltage (VSSHV_REF)
Data Source
AI summary
A floating-rail reference generator and method of operating the same are provided. Generally, the generator includes a tracking current source coupled in series with a current scaling resistor between an input voltage (VBAT) and ground. The tracking current source is operable to receive a reference voltage and couple a tracking current through the resistor to produce a floating-rail reference voltage (VSSHV_REF) at an output between the tracking current source and scaling resistor, wherein: VSSHV_REF=((VBAT−VGS)/k)·1/R·k·R, where VGS is a desired constant potential difference between VBAT and VSSHV_REF, k is a voltage scaling ratio, and R is a resistance of the current scaling resistor. In some embodiments, the tracking current source includes a transistor coupled between VBAT and the output, and controlled by a differential amplifier.