Band-gap Reference Circuit Start-up Method
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Solution Overview
Problem
Band-gap reference circuits experience prolonged settling times and voltage overshots under large load or low power conditions, affecting the stability of reference voltages and potentially damaging external circuits.
Innovation Solution
Incorporating a current source connected to the inputs of the operational amplifier during the start-up phase, which is then disconnected after the phase, allowing charging currents to flow directly to the inputs via switches, bypassing the second node and reducing the settling time and voltage overshots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional start-up circuit is used to enable the band-gap reference circuit during start-up phase, then the circuit can be started up from standby state, but the settling time is prolonged and voltage overshots occur under large load or low power conditions
Solution Approach 1:
The patent segments the start-up process into distinct phases by introducing separate start-up current paths (first and second current paths) that can be independently controlled. The start-up circuit selectively enables different current paths based on operational conditions, allowing optimized charging during start-up phase versus normal operation phase, thereby reducing settling time while maintaining stability.
Solution Approach 2:
The patent applies preliminary action by pre-charging the inputs of the operational amplifier through dedicated start-up current paths before the main reference voltage generation begins. The start-up circuit activates these current paths at the beginning of the start-up phase to quickly establish initial voltages at the amplifier inputs, preventing prolonged settling and voltage overshots that would otherwise occur.
2Ease of operation
If the start-up circuit enables charging currents to flow through the second node during start-up phase, then the operational amplifier inputs can be charged, but voltage overshots occur that may damage external circuits
Solution Approach 1:
The patent introduces an intermediary start-up circuit that mediates between the power supply and the operational amplifier inputs during the start-up phase. This intermediary circuit provides controlled charging current through dedicated paths, preventing direct uncontrolled charging that would cause voltage overshots at the second node, while still ensuring proper initialization of the amplifier inputs.
Solution Approach 2:
The patent applies local quality by providing different current paths with different characteristics for different purposes: the first current path provides controlled charging current to one input of the operational amplifier, while the second current path provides charging current to the other input. Each path is optimized for its specific function, allowing precise control over charging behavior to prevent voltage overshots while ensuring proper start-up.
Data Source
AI summary
A circuit includes a band-gap reference circuit and a start-up circuit. The band-gap reference circuit includes an operational amplifier, a first current path between a power supply node and a reference node, a second current path between the power supply node and the reference node, and a feedback path between an output of the operational amplifier and the first and second current paths. A first input of the operational amplifier is coupled to the first current path, and a second input of the operational amplifier is coupled to the second current path. The start-up circuit includes a current source and at least one switch coupled between the current source and the band-gap reference circuit. The at least one switch is configured to electrically couple the current source with the first and second current paths during a start-up phase.