Op-Amp Start-Up Circuit Layout for Low-Power Fast Biasing
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Solution Overview
Problem
Existing operational amplifier start-up circuits face challenges of high power consumption and complex design, which can affect the normal operation of the amplifier and increase chip area.
Innovation Solution
A start-up circuit for operational amplifiers is designed with a simple structure using two start-up transistors (M16 and M17) connected to a tail bias node and a bias voltage, allowing for quick start-up of the operational amplifier without introducing additional zeros and poles, thus avoiding the need for bandwidth compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing start-up circuits are used, then the operational amplifier can be started, but the power consumption is high and the design is complex
Solution Approach 1:
The start-up circuit is segmented into two independent transistors (M16 and M17) that operate separately during different phases. This segmentation allows each transistor to be optimized for its specific function: M16 provides start-up current while M17 suppresses leakage, simplifying the overall design compared to integrated complex start-up circuits.
Solution Approach 2:
The circuit performs preliminary action by using M16 to establish the initial operating state of the operational amplifier before normal operation begins. Once started, M17 takes over to suppress leakage current, eliminating the need for complex continuous start-up mechanisms.
2Reliability
If existing start-up circuits are used, then the operational amplifier can be started, but the power consumption is high
Solution Approach 1:
The start-up circuit operates periodically rather than continuously. M16 is active only during the start-up phase to provide necessary current, while M17 becomes active after start-up to suppress leakage. This periodic operation dramatically reduces average power consumption compared to traditional circuits that consume power continuously.
Solution Approach 2:
The circuit discards the start-up function after it has served its purpose. Once the operational amplifier is started, M16 is effectively deactivated and its function is recovered by M17 which suppresses leakage current, eliminating unnecessary power consumption from continuous start-up circuit operation.
3Device complexity
If a simple start-up circuit is used, then the design is simplified and power consumption is reduced, but additional zeros and poles are introduced affecting bandwidth
Solution Approach 1:
The start-up transistors are strategically positioned at specific locations in the circuit (connected to the tail bias node and second-stage input terminals) where they can provide start-up current without interfering with the main signal path. This local placement ensures that the simple circuit structure does not introduce additional zeros and poles that would affect bandwidth performance.
Data Source
AI summary
This application provides an operational amplifier and a start-up circuit of the operational amplifier. The start-up circuit has the advantages of having a simple structure and consuming less. The operational amplifier includes a multi-stage amplifier and a start-up circuit, where the start-up circuit includes a first start-up transistor and a second start-up transistor. A source of the first start-up transistor and a source of the second start-up transistor are connected to a tail bias node of a first-stage amplifier in the multi-stage amplifier, a gate of the first start-up transistor and a gate of the second start-up transistor are configured to connect to a first bias voltage Vb, and a drain of the first start-up transistor and a drain of the second start-up transistor are connected to input terminals of a second-stage or higher-stage amplifier.