Sub-Bandgap Reference Voltage Circuit Without Resistor Drift
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Solution Overview
Problem
Existing sub-bandgap reference voltage generators face challenges in stability and variability due to device startup issues and sensitivity to process and temperature variations, particularly in resistor-based designs.
Innovation Solution
A circuit comprising a reference current generator and voltage generator using a combination of bipolar junction transistors and n-channel transistors, with a differential amplifier to produce a temperature-insensitive output reference voltage by balancing currents proportional and complementary to absolute temperature, avoiding resistor-based variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If resistor-based sub-bandgap reference voltage generators are used, then the circuit can generate sub-bandgap voltage, but the output voltage is subject to process variations and resistance variations over temperature
Solution Approach 1:
The patent changes the fundamental parameter used for voltage generation from resistor-based voltage division to a transistor-based current mirror system. By using the exponential current-voltage relationship of bipolar transistors and the square-law relationship of MOS transistors, the circuit generates temperature-compensated voltage without relying on resistor values, thereby eliminating sensitivity to process and temperature variations in resistors.
Solution Approach 2:
The patent substitutes the passive resistor-based voltage division mechanism with an active transistor-based current mirror and differential amplifier system. This replacement allows for dynamic temperature compensation through the inherent temperature-dependent characteristics of transistor junctions, achieving superior temperature independence compared to passive resistor networks.
2Temperature
If known sub-bandgap reference voltage generators are used, then sub-bandgap voltage can be generated, but stability issues occur upon device startup
Solution Approach 1:
The patent incorporates a startup circuit that pre-establishes the correct operating conditions before the main reference voltage generation begins. This preliminary action ensures that the differential amplifier and current mirrors are properly biased from the start, preventing startup instability and ensuring smooth transition to the stable reference voltage state.
Solution Approach 2:
The patent uses an intermediate differential amplifier stage that acts as a mediator between the current mirror circuit and the final output. This intermediate stage provides buffering and signal conditioning that stabilizes the transition during startup and ensures smooth operation throughout the device lifecycle.
3Device complexity
If resistor-based voltage division is used to generate sub-bandgap voltage, then the circuit structure is simple, but the output voltage varies with temperature and process
Solution Approach 1:
The patent creates a composite circuit architecture that combines bipolar junction transistors, MOS transistors, current mirrors, and differential amplifiers into an integrated system. This composite structure leverages the complementary temperature characteristics of different transistor types to achieve temperature-independent voltage generation, overcoming the limitations of simple resistor-based designs.
Solution Approach 2:
The patent implements feedback through the differential amplifier that continuously monitors and corrects the reference voltage output. The differential amplifier compares the generated voltage against a reference and adjusts the current mirror operation to maintain precise voltage output despite process and temperature variations, achieving manufacturing precision without increasing apparent circuit complexity.
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 provides a stable and scalable sub-bandgap reference voltage with low voltage headroom requirements and reduced sensitivity to temperature and process variations, enabling efficient generation of a fraction of the bandgap voltage.
Implementation Method 1
a first bipolar junction transistor having an emitter coupled to a first resistor, a collector coupled to ground, and a base; a second bipolar junction transistor having an emitter, a collector coupled to ground, and a base coupled to the base of the first bipolar junction transistor
Implementation Method 2
a first n-channel transistor having a source coupled to the first resistor and a gate; and a second n-channel transistor having a source coupled to the emitter of the second bipolar junction transistor, a drain, and a gate coupled to the drain of the second n-channel transistor and to the gate of the first n-channel transistor
Implementation Method 3
A differential amplifier has an input coupled to the node and an output generating a temperature insensitive output reference voltage, wherein the differential amplifier is coupled between a supply voltage and the output of the current mirror
Data Source
AI summary
A reference current generator circuit generating a reference current that is proportional to absolute temperature as a function of a difference between bias voltages of first and second transistors. A voltage generator generates an input voltage from the reference current by applying the reference current that is proportional to absolute temperature through a plurality of transistors coupled in series between the bias voltage of the second transistor and ground, with the input voltage being generated at a node between given adjacent ones of the plurality of transistors. The input voltage is complementary to absolute temperature. A differential amplifier is biased by a current derived from the reference current and generates a temperature insensitive output reference voltage from the input voltage and a voltage proportional to absolute temperature.