Reference Current Generator Low Temperature Coefficient
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Solution Overview
Problem
Prior art reference current generator circuits in RFID systems exhibit significant temperature-dependent variations in generated reference currents, leading to increased power consumption and reduced reliability due to currents being proportional to absolute temperature (PTAT), resulting in a 45% variation over a wide temperature range.
Innovation Solution
A reference current generator circuit design that includes a core circuit with a parallel configuration of transistors, where a third transistor with a different threshold voltage counteracts the PTAT characteristics, maintaining a substantially constant voltage differential across a resistive component, thus minimizing temperature variation in the generated current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a prior art reference current generator circuit is used, then the circuit provides a simple current reference, but the generated current varies by 45% over a wide temperature range due to PTAT characteristics
Solution Approach 1:
The patent changes the operating parameters of the transistor by biasing it at a specific current density to exploit the transition region where mobility degradation compensates for thermal effects. This parameter adjustment transforms the temperature dependence from PTAT (positive temperature coefficient) to approximately zero temperature coefficient, resolving the contradiction between reliability and temperature sensitivity.
Solution Approach 2:
The patent converts the harmful temperature-dependent mobility variation into a beneficial compensating effect. By operating in the transition region where mobility degradation with temperature becomes significant, the circuit transforms the temperature sensitivity that would normally cause drift into a stabilizing mechanism that counteracts other temperature effects, achieving low temperature coefficient.
2Reliability
If the reference current is proportional to absolute temperature (PTAT), then the current increases with temperature, but this results in increased power consumption and reduced reliability
Solution Approach 1:
The patent changes the current density parameter of the reference transistor to operate in a specific transition region. This parameter change fundamentally alters the temperature dependence of the current, transforming it from PTAT (increasing with temperature) to approximately constant (independent of temperature). This resolves the contradiction by eliminating the temperature-driven power consumption increase while maintaining reliable operation.
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 a substantially constant current over a wide temperature range, reducing power consumption and enhancing the reliability and performance of RFID tags by minimizing temperature-dependent variations in reference currents.
Implementation Method 1
Prior art reference current generators typically generate currents that are proportional to absolute temperature ('PTAT'), and therefore currents that increase as temperature increases
Implementation Method 2
a voltage is generated across the resistive component being substantially equal to a voltage differential between the first transistor and the second transistor
Data Source
AI summary
Embodiments of the invention describe a core circuit for a reference current generator circuit that biases a first transistor to source a first current and a second transistor parallel to the first transistor, biased to source a second current controlled by the first current. A third transistor is coupled parallel to the second transistor and sources a third current controlled by the first current. The third transistor has a different threshold voltage than a threshold voltage of the second transistor. A resistive component coupled to conduct the second current has a resistive voltage that is substantially equal to a voltage differential between the first transistor and the second transistor. The conducting current through the resistive component is substantially independent of temperature variations.