Bandgap Reference Trimming for Low-Voltage Current Accuracy
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Solution Overview
Problem
Conventional bandgap reference circuits face challenges in generating accurate reference currents and voltages due to the large number of circuit components, which contribute to errors, size, cost, and complexity, especially in achieving temperature independence and process/mismatch variations.
Innovation Solution
A low supply voltage BiCMOS self-biased bandgap reference circuit with a trimming circuit that uses differently-sized bipolar transistors and field effect transistors to generate PTAT and CTAT currents, and a trimming circuit to modify the CTAT current based on a trim control signal, reducing base current contributions and improving accuracy by compensating for temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional bandgap reference circuits use large numbers of circuit components including bipolar transistors to generate accurate reference currents, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts and eliminates unnecessary circuit components from conventional bandgap reference designs. Specifically, it removes redundant transistors and operational amplifiers while retaining only the essential elements (bipolar transistors Q1-Q2, resistors R1-R3, and capacitors C1-C2) needed to generate accurate reference currents, thereby reducing device complexity without sacrificing measurement precision
Solution Approach 2:
The circuit is segmented into functionally distinct blocks: a differential amplifier stage using bipolar transistors Q1-Q2 for temperature compensation, a current generation stage using resistors R1-R3 for setting reference currents, and a filtering stage using capacitors C1-C2 for stabilizing the reference voltage. This segmentation allows each component to be optimized for its specific function, improving overall accuracy while minimizing the total number of components
2Stability of the object's composition
If conventional bandgap reference circuits use multiple bipolar transistors to compensate CTAT voltage, then temperature independence is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs parameter changes by using bipolar transistors Q1 and Q2 with deliberately different emitter areas (different sizing reference values) to generate the PTAT voltage. This parameter differentiation, combined with the temperature-dependent behavior of bipolar transistors, enables automatic temperature compensation without requiring tight manufacturing tolerances on individual components
Solution Approach 2:
The circuit combines different types of components (bipolar transistors for temperature compensation, resistors for current setting, and capacitors for filtering) into a composite structure that achieves temperature independence. The interaction between these heterogeneous components creates a system that is more robust to manufacturing variations than any single component could be
3Stability of the object's composition
If conventional bandgap reference circuits combine PTAT and CTAT currents through multiple circuits, then temperature compensation is improved, but ease of manufacture deteriorates
Solution Approach 1:
The patent merges the PTAT current generation and CTAT current generation into a single integrated circuit block. The bipolar transistors Q1-Q2 simultaneously generate both current components, and the resistors R1-R3 directly convert these to the reference currents without requiring separate dedicated circuits for each current type, thereby simplifying manufacturing while maintaining temperature compensation
Solution Approach 2:
The bipolar transistors Q1 and Q2 serve multiple functions: they generate the PTAT voltage, produce the CTAT currents through their base-emitter junctions, and provide temperature compensation all in the same circuit structure. This multi-functionality eliminates the need for separate specialized circuits, making the design easier to manufacture while achieving effective temperature compensation
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 provides a smaller bandgap reference circuit with improved accuracy and temperature independence, minimizing the need for extra circuitry and achieving low voltage operation with reduced curvature of the bandgap reference voltage over temperature, resulting in more accurate and robust reference currents and voltages.
Implementation Method 1
a first circuit branch connected, respectively, to the first bipolar transistor, to generate a first current that is a proportional to absolute temperature (PTAT)
Implementation Method 2
a second circuit branch connected, respectively, to the second bipolar transistor, to generate a second current that is an inverse or complementary proportional to absolute temperature (CTAT)
Data Source
Figure 1
Figure 2
AI summary
A bandgap reference circuit includes a first current generator having first and second bipolar transistors for generating a first current that varies proportionally as a function of temperature. A second current generator includes a field effect transistor for generating a second current that varies inversely as a function of temperature. A trimming circuit includes a third bipolar transistor sized to match the first bipolar transistor, a third current generator having a second field effect transistor coupled to a collector and base of the third bipolar transistor to generate a third current based on a base current of the third bipolar transistor, and a trim control circuit configured to modify the second current by adding the third current to or subtracting the third current from the second current based on a trim control signal. A bandgap reference current is generated by summing the first current and the modified second current.