CMOS Current Source with PTC-NTC Compensation for Stable Biasing
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Solution Overview
Problem
Current source circuits in semiconductor designs are affected by temperature variations and supply voltage fluctuations, leading to unstable operation, as they typically have temperature-dependent current outputs and require start-up circuits.
Innovation Solution
A ΔVgs-type current source circuit is designed with a combination of PTC and NTC branches, allowing for a controllable temperature coefficient and independence from supply voltage variations, using transistors in the triode region to generate and mirror currents, eliminating the need for a start-up circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional current source circuit is used, then the circuit can deliver current, but the current output is affected by temperature variations and supply voltage fluctuations
Solution Approach 1:
The current source circuit is divided into two separate branches: a PTC current branch and an NTC current branch. Each branch independently generates current with opposite temperature coefficients, allowing their effects to be combined to achieve temperature independence while maintaining stability against supply voltage variations
Solution Approach 2:
The circuit utilizes transistors operating in different regions (saturation region for PTC current generation, triode region for NTC current generation) to achieve different temperature coefficient characteristics. By changing the operating region and electrical parameters of transistors, the circuit generates currents with opposing temperature dependencies that compensate for each other
2Reliability
If transistors are used in current source configuration, then high output impedance is achieved, but temperature variations significantly affect the operation
Solution Approach 1:
The circuit employs counterbalancing by generating two currents with opposite temperature coefficients (PTC and NTC). The PTC current increases with temperature while the NTC current decreases with temperature, and their combination creates a net current that remains stable across temperature variations, effectively canceling out the temperature coefficient effects
3Productivity
If a ΔVgs-type current source is used, then current generation is achieved, but supply voltage variations affect the output current
Solution Approach 1:
The circuit employs feedback mechanisms where the PTC and NTC current branches continuously adjust their output based on temperature conditions. The feedback loop ensures that as supply voltage varies, the temperature-compensated current remains stable by automatically balancing the opposing temperature coefficient effects
4Productivity
If conventional current source designs are used, then current delivery is achieved, but start-up circuits are required to initiate operation
Solution Approach 1:
The dual-branch current source circuit is designed to be self-starting by utilizing the inherent positive feedback characteristics of the PTC and NTC branches. When power is applied, the circuit automatically initiates current flow through the interaction of the two branches without requiring external start-up assistance, as each branch naturally drives the other into operation
Data Source
AI summary
An improved current source may provide an improvement over a typical ΔVgs-type current source. The improved current source may comprise two branches. A first branch may be configured to generate a PTC (proportional to absolute temperature) current based on a ΔVgs developed across a resistor. A second branch may be configured to generate an NTC (inversely proportional to absolute temperature) current. The PTC current and NTC current may be combined to obtain a third current having a magnitude that is the sum of the respective magnitudes of the PTC current and the NTC current, and a temperature coefficient that is a combination of the respective temperature coefficients of the PTC current and NTC current. The current source may be configured to generate the NTC current and PTC current to be substantially insensitive to variations in the supply voltage.