PTAT-Only Reference Generator for Fast Zero-TC Biasing
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Solution Overview
Problem
Integrated bandgap reference (BGREF) circuits in CMOS technology face challenges such as wide output voltage distributions, slow settling times, large area requirements, and high current consumption, especially as transistor architecture scales and degrades, and they typically rely on parasitic bi-polar junction transistors which are not suitable for gate all-around configurations.
Innovation Solution
A bandgap-less apparatus that generates a zero-temperature coefficient (TC) or even constant-temperature (CTAT) reference current or voltage using PTAT-only currents, without the need for native CTAT components or bandgap diodes, through a circuit design that subtracts two different PTAT currents with different temperature coefficients, ensuring process, voltage, and temperature (PVT) insensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If parasitic BJT-based BGREF circuits are used to generate temperature independent reference voltage, then near zero TC voltage is achieved by canceling CTAT and PTAT voltages, but the output voltage distribution becomes too wide due to degradation of BJT ideality factor as CMOS technology scales
Solution Approach 1:
The patent extracts and eliminates the dependency on parasitic BJT components from the reference voltage generation circuit. By removing the BJT-based CTAT voltage generation mechanism, the circuit avoids the degradation of BJT ideality factor that causes wide output voltage distribution, while still achieving temperature independence through alternative PTAT current subtraction methods
Solution Approach 2:
The patent changes the fundamental operating parameters by transitioning from voltage-based BGREF operation to current-based operation. It uses proportional-to-absolute-temperature (PTAT) currents with different temperature coefficients that are subtracted to produce a temperature-independent reference current, fundamentally altering how temperature compensation is achieved
2Measurement precision
If traditional BGREF circuits are implemented in sub 10 nm CMOS process, then reference voltage is generated, but the circuit becomes slow to settle (approximately 1-4 μs) and consumes high current (approximately 700 μA)
Solution Approach 1:
The patent substitutes the traditional voltage-based feedback mechanism with a current-based direct subtraction approach. By using current mirrors to subtract PTAT currents with different temperature coefficients, the circuit eliminates the need for slow-settling operational amplifiers and feedback loops, achieving faster settling while maintaining reference stability
3Measurement precision
If parasitic BJT-based BGREF circuits are used in gate all-around transistor architecture, then reference voltage generation is attempted, but enabling high quality BJTs becomes even more challenging
Solution Approach 1:
The patent extracts the reference generation function from parasitic BJT components and implements it using standard CMOS transistors in gate all-around architecture. By eliminating the requirement for high-quality parasitic BJTs, the design becomes compatible with modern CMOS manufacturing processes where gate all-around transistors are the standard
4Measurement precision
If bandgap diodes and operational amplifiers are used in BGREF circuits, then temperature compensation is achieved, but the circuit area becomes large (approximately 70×90 μm²) and design complexity increases
Solution Approach 1:
The patent extracts and removes the bandgap diode and operational amplifier components from the reference circuit. By using simple current mirrors and direct PTAT current subtraction, it achieves temperature independence through a compact design that eliminates large-area components while maintaining PVT insensitivity
Solution Approach 2:
The patent changes from voltage-mode operation with operational amplifiers to current-mode operation with direct current subtraction. This parameter change enables a much smaller circuit area by eliminating the need for high-gain amplifiers and large bandgap diodes, achieving the same temperature compensation function with significantly reduced footprint
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 achieves fast settling times, reduced area, lower current consumption, and a simple design by eliminating the need for operational amplifiers and bandgap diodes, providing a PVT-insensitive reference suitable for various applications like voltage regulators and current-starved ring oscillators.
Implementation Method 1
a first circuit to generate a first reference current with a first temperature coefficient; a second circuit to generate a second reference current with a second temperature coefficient, wherein the first circuit is coupled to the second circuit via a node such that the second reference current is subtracted from the first reference current at the node
Data Source
AI summary
The bandgap-less apparatus is a fast settling circuit (e.g., with settling time of less than 40 ns) that can leverage proportional-to-absolute-temperature only (PTAT-only) currents to generate a zero or substantially zero temperature coefficient, or even complementary-to-absolute-temperature (CTAT), reference current or voltage, without the need of a native CTAT component or bandgap diodes. The apparatus subtracts two different PTAT currents so that the resulting current is zero-TC. The resulting current is a reference current. The resulting current can be converted to a reference voltage.