Parallel Transistor Current Reference Circuit
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Solution Overview
Problem
Conventional current reference generator circuits face significant errors due to the spread of bandgap reference voltage and resistance variations with process corners, leading to temperature and process uncompensation issues.
Innovation Solution
A reference current path utilizing two transistors in parallel, biased by different voltages with opposite temperature coefficients, where one is biased by a bandgap voltage and the other by a proportional to absolute temperature (PTAT) voltage, effectively canceling out temperature coefficients and reducing process variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional current reference generator circuit using a single transistor biased by bandgap voltage is used, then the circuit structure is simple, but the reference current has high temperature coefficient and significant process variation errors
Solution Approach 1:
The current reference circuit is segmented into multiple parallel transistor branches (first transistor branch with first transistor, second transistor branch with second transistor). Each branch has its own biasing circuit and operates with different temperature characteristics. This segmentation allows combining devices with complementary temperature coefficients to achieve overall temperature compensation while maintaining reasonable circuit complexity.
Solution Approach 2:
The invention changes the biasing parameters by applying different voltages to the control terminals of parallel transistors. Specifically, the first transistor is biased by a first voltage and the second transistor is biased by a second voltage, where these voltages have different temperature coefficients. This parameter change enables the transistors to exhibit opposite temperature coefficients in their drain currents, achieving temperature compensation when the currents are combined.
2Ease of manufacture
If the resistance of resistor R1 is used for current reference generation, then the circuit is simple to manufacture, but the resistance value has more than ±30% spread with process variation leading to significant errors
Solution Approach 1:
The invention changes from using a single resistor with fixed resistance value to using multiple transistors with controllable electrical parameters. By biasing the transistors with voltages having different temperature coefficients, the effective resistance seen by the reference current path becomes dynamically adjustable and temperature-compensated, achieving manufacturing precision independent of resistor process variations.
Solution Approach 2:
The current reference circuit uses a composite structure combining multiple transistor devices with different biasing characteristics. The first transistor and second transistor, with their opposite temperature coefficients, act as composite elements whose combined effect compensates for individual device variations and environmental changes, achieving superior manufacturing precision.
3Device complexity
If a single transistor biased by bandgap voltage is used for current reference, then the biasing circuit is simple, but the reference current exhibits significant temperature dependence
Solution Approach 1:
The biasing system is segmented into multiple independent biasing circuits, each providing different voltage characteristics. The first biasing circuit generates a first voltage with a certain temperature coefficient, while the second biasing circuit generates a second voltage with an opposite temperature coefficient. This segmentation allows the system to leverage complementary temperature behaviors to achieve compensation.
Solution Approach 2:
The invention applies counterweight by using transistors with opposite temperature coefficients to balance each other's temperature dependence. The first transistor's drain current has a positive temperature coefficient while the second transistor's drain current has a negative temperature coefficient. When these currents are combined in the reference current path, they counterbalance each other's temperature effects, achieving low overall temperature coefficient.
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 low temperature coefficient for the reference current, significantly reducing errors and improving temperature and process compensation, resulting in a more stable reference current generation with minimal spread across different process corners.
Implementation Method 1
the first and second transistors are coupled in parallel with each other; and wherein a temperature coefficient of the current flowing in the first transistor and a temperature coefficient of the current flowing in the second transistor are opposite
Data Source
AI summary
A reference current path carries a reference current. A first transistor is coupled to the reference current path. A second transistor is also coupled to the reference current path. The first and second transistors are connected in parallel to carry the reference current. The first transistor is biased by a first voltage (which is a bandgap voltage plus a threshold voltage). The second transistor is biased by a second voltage (which is a PTAT voltage plus a threshold voltage). The first and second transistors are thus biased by voltages having different and opposite temperature coefficients with a result that the temperature coefficients of the currents flowing in the first and second transistors are opposite and the reference current accordingly has a low temperature coefficient.