Bandgap Current Reference with Single PTAT Path Stability
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Solution Overview
Problem
Existing bandgap current reference circuits face challenges in achieving precise temperature stability and reducing circuit area and component mismatch, leading to multiple stable operating points and increased trim requirements.
Innovation Solution
The proposed bandgap current reference circuits incorporate a bandgap core circuit with a bipolar transistor and resistors, coupled with an error amplifier featuring a differential input stage, which ensures a single stable operating point and reduces circuit area by using a single PTAT path and a CTAT leg, eliminating undesirable operational modes through integrated differential pairs within the error amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If traditional bandgap current reference circuits are used, then temperature stability can be achieved, but circuit area increases and multiple stable operating points appear
Solution Approach 1:
The patent combines the PTAT current generation and error amplification functions into a single integrated circuit block. The error amplifier's differential input stage directly processes signals from the PTAT current path, eliminating the need for separate monitoring circuits and reducing overall circuit area while maintaining temperature stability through the combined feedback mechanism.
Solution Approach 2:
The error amplifier is designed to serve multiple functions: it amplifies the differential voltage from the PTAT current path, provides feedback control to the bandgap core circuit, and ensures single stable operating point through its differential input stage. This multi-functionality reduces the need for additional dedicated circuits, thereby reducing circuit area.
2Reliability
If multiple PTAT paths are used to ensure stable operation, then reliability improves, but circuit area and component mismatch increase
Solution Approach 1:
The patent merges the functions of multiple PTAT paths into a single integrated error amplifier circuit. The differential input stage of the error amplifier processes the PTAT current signal while providing feedback control, eliminating the need for separate monitoring and control circuits. This integration maintains reliable stable operation while reducing circuit complexity and component mismatch.
3Stability of the object's composition
If larger emitter areas are used in bipolar transistors, then temperature stability improves, but circuit area increases
Solution Approach 1:
The patent combines the temperature compensation function into the error amplifier's feedback mechanism rather than relying solely on large emitter area transistors. The error amplifier processes the differential voltage from the PTAT current path and adjusts the bandgap core circuit to maintain temperature stability, allowing the use of smaller transistor emitters while achieving the same temperature stability performance.
4Measurement precision
If trim requirements are increased to compensate for variation, then precision improves, but manufacturing cost and complexity increase
Solution Approach 1:
The patent employs an error amplifier with feedback control that automatically compensates for variations in reference current due to temperature, voltage, and process changes. The differential input stage detects deviations from the desired operating point and adjusts the bandgap core circuit accordingly, maintaining high precision without requiring additional trim components or complex calibration procedures, thereby simplifying manufacturing.
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 reduced circuit area, improved power supply rejection, and minimized variation in reference current over temperature, voltage, and process, thereby reducing trim requirements and associated costs.
Implementation Method 1
The bipolar transistor is configured to pass a current that is proportional to absolute temperature (PTAT current)
Implementation Method 2
The bandgap reference circuit combines the PTAT and CTAT voltages or currents such that their respective temperature coefficients cancel each other out to produce a temperature stable voltage or current
Data Source
AI summary
A bandgap current reference circuit includes a bandgap core circuit and an error amplifier. The bandgap core circuit is configured to generate a zero temperature coefficient bandgap current. The bandgap core circuit includes a bipolar transistor. The bipolar transistor is configured to pass a current that is proportional to absolute temperature (PTAT current). The error amplifier is coupled to the bandgap core circuit and includes a bipolar differential input pair. The bipolar differential input pair is configured to ensure that the PTAT current is flowing in the bipolar transistor.