CMOS Process Insensitive Current Reference Circuit
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Solution Overview
Problem
Smart temperature sensors manufactured with CMOS technology face limitations due to process variations, resulting in limited operating ranges and relatively low accuracy, which is exacerbated by the need for complex trimming techniques that increase silicon area and costs.
Innovation Solution
A CMOS-based process insensitive current reference circuit is developed, utilizing a constant transconductance circuitry with current mirrors and a resistive transistor to maintain a constant resistance value, independent of process variations, and includes feedback circuitry to adjust the reference voltage, thereby generating a constant electric current that is insensitive to manufacturing process variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If trimming techniques (one-point or two-point) are employed to compensate for process variations, then measurement precision is improved, but device complexity increases and silicon area increases
Solution Approach 1:
The bandgap reference circuit automatically compensates for process variations through its inherent feedback mechanism. The circuit self-adjusts by using the temperature-dependent characteristics of bipolar transistors to generate a stable reference voltage that is insensitive to manufacturing variations, eliminating the need for external trimming operations or additional compensation components.
Solution Approach 2:
The patent implements a feedback mechanism where the bandgap reference circuit continuously monitors and adjusts its output based on the temperature-dependent behavior of bipolar transistors. This feedback loop ensures that process variations are automatically compensated, maintaining measurement precision without requiring complex trimming circuitry or additional components.
2Measurement precision
If trimming techniques are used to compensate for process variations, then measurement precision is improved, but the silicon area increases
Solution Approach 1:
The patent merges the temperature sensing function with the bandgap reference circuit into a single integrated structure. By combining these functions, the circuit achieves process variation compensation and accurate temperature measurement without requiring separate trimming components or additional silicon area, as the compensation is inherent to the unified circuit design.
Solution Approach 2:
The bandgap reference circuit serves multiple functions simultaneously: it provides a stable voltage reference, compensates for process variations, and enables accurate temperature sensing. This multi-functionality eliminates the need for separate trimming circuits or additional components, thereby reducing the overall silicon area while maintaining measurement precision.
3Ease of manufacture
If standard CMOS technology is used for manufacturing smart temperature sensors, then ease of manufacture is improved, but manufacturing precision deteriorates due to process variations
Solution Approach 1:
The patent converts the harmful effect of process variations into a beneficial feature by exploiting the temperature-dependent characteristics of bipolar transistors. The circuit is designed to use these variations to generate a stable bandgap reference voltage that is inherently insensitive to manufacturing process deviations, thereby maintaining manufacturing simplicity while achieving high precision without requiring additional trimming or compensation components.
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
This solution improves the accuracy of smart temperature sensors by reducing their dependence on process variations, achieving accuracy within ±1.5°C to ±1.45°C without the need for trimming techniques, while maintaining a smaller silicon area and lower costs compared to conventional single-chip temperature sensors.
Implementation Method 1
feedback circuitry coupled with the first current mirror, the second current mirror, and the resistive transistor to maintain the resistance value of the resistive transistor at or around a constant resistance value
Implementation Method 2
constant transconductance circuitry comprising a first current mirror and a second current mirror and generating a constant electric current across one or more process corners
Data Source
AI summary
Disclosed are apparatuses and methods for implementing CMOS-based, process insensitive current reference circuit(s). An apparatus includes a constant transconductance circuitry including a first and second current mirrors and respectively generating constant currents across one or more process corners, a resistive transistor in the constant transconductance circuitry having a resistance, and a feedback circuitry coupled with the resistive transistor and the constant transconductance circuitry to form a constant current source. The apparatus may optionally include a data processing module as well as another constant transconductance circuitry, another resistive transistor, and another feedback circuitry that form another constant current source. A method for implementing a system on chip may identify first and second currents generated by process insensitive current circuits, determine first and second temperature dependent voltages, and generate a digital output by transforming the first and second temperature dependent voltages.