Sub-Bandgap Reference Voltage Circuit for Stable Startup and Output
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Solution Overview
Problem
Existing sub-bandgap reference voltage generators face issues with stability upon startup and are susceptible to variations due to process and temperature-related changes in resistors, leading to inconsistent output.
Innovation Solution
A circuit comprising a reference current generator, a voltage generator, and a differential amplifier that produces a temperature-insensitive output by summing currents proportional and complementary to absolute temperature, using a configuration of bipolar junction transistors and field effect transistors to generate a sub-bandgap reference voltage, avoiding resistor-based variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If resistor-based sub-bandgap reference voltage generation is used, then the circuit can generate sub-bandgap voltage, but the output is subject to process variations and temperature-related resistance changes
Solution Approach 1:
The patent extracts and eliminates the resistor component from the reference voltage generation path. By using a current mirror configuration with bipolar junction transistors and field effect transistors, the circuit generates the sub-bandgap reference voltage without relying on resistor values, thereby removing the source of process and temperature variations associated with resistors.
Solution Approach 2:
The patent replaces the resistor-based voltage division mechanism with a transistor-based current mirror and voltage generation mechanism. The mechanical/electrical system of resistor voltage division is substituted with a semiconductor-based system using BJT and FET devices that generate voltage through controlled current flow and transistor characteristics, which are less sensitive to process variations.
2Measurement precision
If known sub-bandgap generators are used, then sub-bandgap voltage can be generated, but stability upon device startup is compromised
Solution Approach 1:
The patent implements preliminary action by ensuring the reference current generator and voltage generator are properly biased and initialized before the differential amplifier operates. The circuit configuration ensures that the PTAT and CTAT currents are established in advance, providing a stable foundation for the differential amplifier to produce the reference voltage, thereby ensuring startup stability.
3Ease of manufacture
If resistor-based voltage generation is used, then circuit implementation is straightforward, but the circuit is susceptible to process and temperature variations
Solution Approach 1:
The patent replaces the resistor-based voltage generation mechanism with a transistor-based system. The current mirror configuration using BJT and FET devices provides a manufacturing approach that is equally straightforward but yields superior voltage consistency by eliminating resistor process variations. The transistor-based current mirrors and voltage generators can be implemented using standard CMOS or bipolar process steps.
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 head-room requirements and easy scaling, reducing temperature dependence and process variations, resulting in a consistent output.
Implementation Method 1
The reference current generator is configured to generate a reference current that is proportional to absolute temperature
Implementation Method 2
The voltage generator is configured to generate an input voltage from the reference current, with the input voltage being complementary to absolute temperature
Implementation Method 3
generate a current proportional to absolute temperature as a function of a difference between base to emitter voltages of first and second bipolar junction transistors
Implementation Method 4
generate a voltage complementary to absolute temperature by applying the current proportional to absolute temperature through a plurality of field effect transistors coupled in series
Data Source
AI summary
A sub-bandgap reference voltage generator includes a reference current generator generating a reference current (proportional to absolute temperature), a voltage generator generating an input voltage (proportional to absolute temperature) from the reference current, and a differential amplifier. The differential amplifier is biased by the reference current and has an input receiving the input voltage and a resistor generating a voltage proportional to absolute temperature summed with the input voltage to produce a temperature insensitive output reference voltage. The reference current generator may generate the reference current as a function of a difference between bias voltages of first and second transistors. The voltage generator may generate the input voltage by applying the current proportional to absolute temperature through a plurality of transistors coupled in series between the bias voltage of the second transistor and ground, and tapping a node between given adjacent ones of the plurality of transistors.