Diode-Connected MOS Start-Up Circuit for Bandgap Reference Stability
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Solution Overview
Problem
Conventional start-up circuits for voltage and current reference circuits in integrated circuits are sensitive to variations in power supply voltage and process parameters, leading to instability and high power consumption, particularly in power-aware applications like energy harvesting systems.
Innovation Solution
A start-up circuit with a diode-connected transistor and a current source, matched to the current control transistor, that uses switch logic to control switches based on the reference circuit's current, ensuring minimal power consumption and stability by eliminating current flow after startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional start-up circuits are used for voltage and current reference circuits, then the reference circuit can be initialized, but the start-up circuit consumes high power and exhibits instability due to sensitivity to power supply voltage and process parameter variations
Solution Approach 1:
The start-up circuit activates preliminary current paths through transistors M1-M4 and current sources I1-I2 to initialize the reference circuit before normal operation begins. This preliminary action ensures the reference circuit reaches its operating point without requiring continuous power consumption afterward.
Solution Approach 2:
The start-up circuit is designed as a separate, extractable module that can be independently controlled and disabled. Once the reference circuit is initialized, the start-up circuit is turned off through control signals, removing its power consumption from the system while maintaining its initialization function.
2Speed
If conventional start-up circuits with high gain loops are used, then startup can be achieved, but the circuit exhibits instability and sensitivity to process and voltage variations
Solution Approach 1:
The start-up circuit uses controlled current parameters through current sources I1 and I2 that can be adjusted independently of high gain loops. By changing current parameters rather than relying on high gain voltage amplification, the circuit achieves fast startup while maintaining stability against PVT variations.
Solution Approach 2:
The patent introduces intermediate control signals and current mirrors as mediators between the start-up circuit and the reference circuit. These intermediaries buffer the startup process from direct feedback loops, reducing sensitivity to PVT variations while maintaining controlled startup speed.
3Reliability
If the start-up circuit remains active continuously, then the reference circuit can be maintained, but power consumption increases significantly in power-aware applications
Solution Approach 1:
The start-up circuit operates periodically rather than continuously - it activates to initialize the reference circuit and then enters a low-power standby state. Control logic monitors the reference circuit status and reactivates the start-up circuit only when initialization is needed, eliminating continuous power consumption.
Solution Approach 2:
The reference circuit monitors its own operational status and automatically triggers the start-up circuit when initialization is required. This self-service mechanism eliminates the need for continuous monitoring and control circuitry, reducing standby power consumption while ensuring the reference circuit remains operational.
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 provides a stable, power-efficient start-up circuit that quickly settles the reference circuit, is scalable, and reduces power consumption to nearly zero post-startup, making it suitable for energy harvesting and other power-aware systems.
Implementation Method 1
a diode-connected start-up transistor constructed in a matching manner relative to the current control transistor
Implementation Method 2
a current source coupled in series with the start-up transistor. In start-up, the current conducted by the current source turns on the start-up transistor
Implementation Method 3
switch logic controls switches in the start-up circuit in response to a current generated by the reference circuit, to eliminate current consumption in the start-up circuit after start-up
Data Source
AI summary
A start-up circuit for a reference circuit such as a bandgap reference circuit. The start-up circuit includes a diode-connected metal-oxide-semiconductor (MOS) transistor connected between a power supply node and a start-up node that is connected in turn to the gate of a current control MOS transistor in the reference circuit. The diode-connected MOS transistor and the current control MOS transistor are matched with one another. To start up the reference circuit, current is conducted through the diode-connected MOS transistor to set the gate voltage of the current control transistor at a threshold voltage below the power supply voltage. Current conducted by the current control transistor initiates operation of the bandgap reference circuit, and disables the start-up circuit.