Bandgap Reference Circuit Using Mirrored PTAT Current for Low Noise
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Solution Overview
Problem
Bandgap reference circuits face challenges in achieving high precision and low noise while maintaining a small circuit area, as increasing PTAT current to reduce noise can lead to increased current density and temperature drift errors, and existing methods to increase PTAT current often require larger transistor sizes.
Innovation Solution
The implementation of current mirroring techniques in bandgap reference circuits, which split and scale up PTAT current without increasing the size of transistors, reducing the scaling factor K and output noise while maintaining a compact circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If PTAT current is increased to reduce noise, then output noise is reduced, but current density increases causing temperature drift errors
Solution Approach 1:
The patent segments the PTAT current path into multiple parallel branches with different current densities. By using multiple transistors operating in parallel, the total PTAT current is divided among them, allowing the circuit to achieve high total current (low noise) while maintaining low current density in each individual transistor (low temperature drift).
Solution Approach 2:
Different transistors are designed with different emitter areas to create local variations in current density. Some transistors operate at higher current densities while others operate at lower current densities, but the weighted average maintains optimal temperature characteristics. This local differentiation allows simultaneous optimization of noise and temperature drift.
2Object-generated harmful factors
If PTAT current is increased to reduce noise, then output noise is reduced, but transistor area increases
Solution Approach 1:
The patent merges multiple transistor branches in parallel to achieve the desired total PTAT current. By combining several smaller transistor instances rather than using one large transistor, the circuit achieves the required current level for low noise operation while the distributed structure allows better area utilization and reduced overall footprint.
3Reliability
If transistor size is increased to reduce temperature drift, then temperature stability is improved, but circuit area increases
Solution Approach 1:
Instead of using a single large transistor, the patent segments the functionality across multiple smaller transistors operating in parallel. Each transistor contributes to the overall temperature stability through its specific current density characteristics, achieving the same temperature stability as a large transistor would provide, but with reduced total area and better current distribution.
Data Source
AI summary
A bandgap reference circuit includes an amplifier, a first transistor, a second transistor, a third transistor, a first resistor, and a second resistor. The amplifier is configured to generate a bandgap voltage. The first transistor is coupled to the amplifier, and passes a first PTAT current. The second transistor is coupled to the amplifier, and passes a second PTAT current. The first resistor is coupled to the amplifier and the second transistor, and passes the second PTAT current to the second transistor. The third transistor is coupled to the amplifier, and passes a third PTAT current that bypasses the first resistor and the second transistor. The second resistor is coupled to the first transistor, the second transistor, and the third transistor, and passes the first PTAT current, the second PTAT current, and the third PTAT current.