Bandgap Reference Start-Up Circuit for Stable Diode Conduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional bandgap reference circuits face unpredictable and unstable start-up characteristics, particularly when the voltage across diodes is below the forward bias voltage, leading to failed or unstable operational states, which complicates detection of undesirable operating points.
Innovation Solution
A start-up circuit that samples current through diodes and injects current into the PTAT and CTAT networks until the current exceeds a pre-designated low value, ensuring stable operation by maintaining current flow through the diodes for proper conduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bandgap reference circuitry is used, then the circuit can operate with standard components, but the start-up characteristics become unpredictable and unstable when voltage across diodes is below forward bias voltage
Solution Approach 1:
The patent applies preliminary action by implementing a start-up circuit that proactively forces current through the PTAT and CTAT networks before the main bandgap reference operation begins. This preliminary current forcing ensures diodes are properly biased and conducting before normal operation, preventing the unpredictable start-up behavior that occurs when diode voltage is below forward bias threshold. The start-up circuit activates first to establish proper operating conditions.
Solution Approach 2:
The patent uses an intermediary approach by introducing a dedicated start-up circuit as a mediator between the power supply and the main bandgap reference circuitry. This intermediary circuit includes current-forcing transistors that temporarily modify the operating conditions of the PTAT and CTAT networks during start-up, allowing the main circuit to achieve stable operation without directly exposing it to the problematic low-voltage start-up conditions.
2Use of energy by moving object
If the voltage across diodes is kept low to reduce power consumption, then power efficiency improves, but the diodes fail to conduct properly causing unstable operation
Solution Approach 1:
The start-up circuit performs preliminary action by temporarily forcing higher current through the PTAT and CTAT networks to establish proper diode conduction before normal low-power operation begins. This preliminary high-current phase ensures diodes are properly biased, after which the circuit can transition to lower power consumption modes while maintaining stable operation.
Solution Approach 2:
The patent implements periodic action through the start-up circuit that operates in phases: initially forcing high current to establish conduction, then transitioning to normal operation. The start-up circuit activates only during the start-up phase and deactivates during normal operation, creating a periodic pattern of high-current initialization followed by low-power steady-state operation.
Data Source
AI summary
A start-up circuit for a bandgap reference circuit includes a sampling circuit for sampling current through a diode in one of first and second diode/resistor networks that respectively provide complementary PTAT and CTAT characteristics in the bandgap reference, and a current injection circuit to inject current to a PMOS bus of the bandgap reference if the sampled current is not higher than a pre-designated low value. By virtue of this operation, since current through the diode itself is sampled, the start-up circuit ensures that current through the sampled diode is higher than the pre-designated low value, thereby leading to rapid start-up of the bandgap reference to a stable operating point.