Reference Voltage Circuit Reducing Process Variation Sensitivity
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Solution Overview
Problem
Traditional bandgap reference voltage circuits are sensitive to semiconductor process variations, leading to variations in reference voltage values from process to process, lot to lot, and even from die to die on the same wafer.
Innovation Solution
A bandgap reference voltage circuit is designed to provide a reference voltage based on a Proportional-To-Absolute Temperature (PTAT) base-emitter voltage difference, reducing dependency on semiconductor process variations by using an amplifier, a first load element, and a feedback load element, where first and second PTAT currents and a CTAT current are arranged to generate a reference voltage that is less process-dependent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a traditional bandgap reference voltage circuit is used, then temperature insensitivity is achieved, but sensitivity to semiconductor process variations increases
Solution Approach 1:
The patent changes the fundamental parameters of the reference voltage circuit by eliminating the exponential relationship with Vbe and replacing it with a linear relationship based on PTAT voltage. This is achieved by using operational amplifiers to force equal voltages at input terminals, thereby deriving reference voltage from resistor ratios and base-emitter voltage differences rather than direct Vbe exponentiation, making the circuit less sensitive to process variations while maintaining temperature insensitivity
Solution Approach 2:
The patent substitutes the traditional bipolar transistor exponential I-V relationship mechanism with an operational amplifier-based voltage comparison and feedback mechanism. By using op-amps to enforce voltage equality at input terminals and deriving the reference voltage from linear PTAT relationships rather than exponential Vbe relationships, the circuit replaces a process-sensitive mechanism with a more robust linear mechanism
2Reliability
If bandgap reference voltage circuit is used, then reliable reference voltage is provided, but variation from process to process and die to die occurs
Solution Approach 1:
The patent changes the dependency parameters from exponential Vbe relationships to linear PTAT voltage relationships based on resistor ratios. By using operational amplifiers to force equal voltages at their input terminals and deriving reference voltage from the difference in base-emitter voltages of bipolar transistors operating at different current densities, the circuit achieves reliability while minimizing process and die-to-die variations
Solution Approach 2:
The patent employs operational amplifiers in feedback configurations where the output is fed back to the inverting input, forcing the voltages at the input terminals to be equal. This feedback mechanism ensures that the reference voltage is determined by stable resistor ratios and PTAT voltage differences rather than by process-sensitive transistor parameters, thereby improving reliability and reducing variation
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 results in a reference voltage with reduced process dependencies, allowing for accurate and scalable voltage references with minimal variations across different semiconductor processes, and the ability to easily trim the voltage to desired values.
Implementation Method 1
the amplifier A forces the voltage at the inverting input to be equal to the voltage at the non-inverting input
Implementation Method 2
a base-emitter voltage difference (ΔVbe) is developed across the resistor r1. Where: k is the Boltzmann constant; q is the charge on the electron; T is operating temperature in Kelvin
Implementation Method 3
One of the voltages is a Complementary-To-Absolute Temperature (CTAT) voltage typically provided by a base-emitter voltage of a forward biased bipolar transistor whose response is temperature dependent and reduces with increasing temperatures
Data Source
AI summary
A reference voltage circuit which is less dependent on semiconductor process variations compared to bandgap based reference voltage circuits. The circuit comprises a first amplifier having an inverting input, a non-inverting input and an output. A current biasing circuit provides first and second PTAT currents, and a CTAT current. The CTAT current is equal in value to the second PTAT at a first predetermined temperature and opposite in polarity. A first load element is coupled to the non-inverting input of the first amplifier and arranged for receiving the first PTAT current such that a PTAT voltage is developed across the first load element. A feedback load element is coupled between the inverting input and the output of the amplifier for receiving the summation of the CTAT current and the second PTAT current. The feedback load element is such that at a second predetermined temperature the voltage at the output of the amplifier is substantially equal to the voltage at the output of the amplifier at the first temperature.