Fully Isolated NPN Bandgap Reference Circuit
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Solution Overview
Problem
Existing bandgap voltage references face challenges in achieving temperature stability due to mismatched magnitudes of temperature coefficients in PTAT and CTAT voltage references, which prevents complete cancellation of temperature coefficients, and resistor temperature coefficients can affect current generation.
Innovation Solution
The solution involves generating and scaling PTAT and CTAT currents to ensure equal magnitudes of temperature coefficients, combining them to form a constant current that is temperature-independent, and using a fully isolated NPN-based bandgap reference circuit with matched transistors and resistors to maintain stability across temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If PTAT and CTAT voltage references are combined to generate temperature-stable voltage, then temperature coefficient cancellation is achieved, but mismatched magnitudes of temperature coefficients prevent complete cancellation
Solution Approach 1:
The patent applies parameter changes by scaling the PTAT current through a resistor ratio (R2/R1) to adjust its magnitude. By changing the resistance values, the scaled PTAT current achieves precise magnitude matching with the CTAT current, enabling complete temperature coefficient cancellation. This is expressed in the patent as scaling the PTAT current to have the same magnitude as the CTAT current through resistor ratio adjustment.
2Productivity
If resistors are used in the bandgap reference circuit, then current generation and voltage scaling are enabled, but resistor temperature coefficients affect current generation and reduce stability
Solution Approach 1:
The patent employs feedback by using the bandgap reference voltage (Vbg) to control the current through the resistors. The circuit forms a feedback loop where Vbg regulates the current generation, compensating for resistor temperature coefficient effects. This feedback mechanism ensures that the current remains stable across temperature variations, as the bandgap voltage's temperature independence compensates for resistor drift.
3Reliability
If a fully isolated NPN-based circuit is used, then substrate charge carrier injection is prevented, but circuit complexity increases due to isolation requirements
Solution Approach 1:
The patent applies segmentation by dividing the circuit into isolated NPN transistor sections with dedicated current paths. Each transistor (Q1, Q2) and its associated resistors form isolated segments that prevent charge carrier injection from the substrate. The circuit is segmented such that only solid nodes (ground, voltage supply) couple with the substrate, while signal nodes remain isolated. This segmentation achieves full isolation without requiring complex additional isolation structures.
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 approach effectively cancels out temperature coefficients, providing a stable voltage reference that remains constant across temperature variations, and compensates for resistor variations, ensuring accurate temperature sensing and voltage generation.
Implementation Method 1
the base-emitter voltage decreases, thereby causing the current through resistor 108 to be the CTAT current, ICTAT
Implementation Method 2
the increasing difference in the base-emitter voltages of transistors 102, 104 cause the current flowing through the resistor 109 to increase, thereby causing the voltage across the resistor 109 to increase as temperature increases. Thus, the current flowing through resistor 109 forms the PTAT current, IPTAT
Implementation Method 3
the control circuit 120, which mirrors the voltages and currents between the nodes 110, 115. In other words, the voltages at nodes 110 and 115 are substantially equal and the current flowing from nodes 110 and 115 into the control circuit 120 are also substantially equal
Data Source
AI summary
Generating a bandgap reference by generating a first current in a first circuit and a second current in a second circuit, a control circuit forcing the first and second currents to have a first magnitude proportional-to-temperature. Generating a third current in a third circuit having a second magnitude based on a first voltage associated with the first circuit, the second magnitude being complementary-to-temperature. Adding the first and second magnitudes in a fourth circuit to form a third magnitude substantially constant over change in temperature, the fourth circuit generating a fourth current having the third magnitude. Adding the first and second magnitudes to generate a fifth current having the first magnitude in a fifth circuit and a sixth current having the second magnitude in a sixth circuit, the fifth and sixth circuits sinking current from the fourth circuit.