Semiconductor Integrated Circuit Start-Up Circuit Design
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Solution Overview
Problem
In semiconductor integrated circuits, low threshold voltage transistors used in constant current circuits lead to high off-leak currents, especially at higher temperatures, causing start-up issues due to premature charging of nodes before the power source voltage reaches the required level, resulting in failure to initiate the constant current circuit.
Innovation Solution
The semiconductor integrated circuit design incorporates a start-up section with a P channel MOS transistor having a higher threshold value and a capacitance element, allowing for stable start-up even with slow power voltage rises by ensuring the P channel MOS transistor remains in an on-state, providing consistent current to the constant current circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If low threshold voltage transistors are used in constant current circuits, then low voltage operation is enabled, but off-leak currents increase causing premature node charging and start-up failure
Solution Approach 1:
A start-up circuit is introduced as an intermediary component between the power source and the constant current circuit. This start-up circuit includes a start-up transistor that temporarily provides a start-up current path, enabling the constant current circuit to initialize before the off-leak current of the low threshold voltage transistors becomes dominant. The start-up circuit acts as a mediator that facilitates proper circuit initialization while the main circuit uses low threshold voltage transistors for low voltage operation.
2Speed
If slow power voltage rise occurs, then low threshold voltage transistors generate sufficient off-leak current to charge nodes prematurely, but the constant current circuit cannot start up
Solution Approach 1:
The start-up circuit performs preliminary action by establishing the initial current flow path before the constant current circuit becomes operational. The start-up transistor is designed to conduct during the voltage rise phase, preemptively creating the necessary current conditions. This preliminary current establishment ensures that when the constant current circuit eventually activates, the nodes are already in the correct voltage state, preventing start-up failure even when power voltage rises slowly.
3Temperature
If high temperature conditions occur, then off-leak current increases, but the start-up circuit must remain stable
Solution Approach 1:
Different threshold voltage characteristics are applied to different transistors in different circuit regions. The constant current circuit uses low threshold voltage transistors optimized for low voltage operation, while the start-up circuit uses high threshold voltage transistors optimized for temperature stability and leak current suppression. This local differentiation of transistor characteristics allows each circuit block to operate optimally under the given conditions, with the start-up circuit remaining stable even at high temperatures.
Data Source
AI summary
A semiconductor integrated circuit provided with: a transistor M7 with a control terminal supplied with a second voltage GND, a first terminal connected to a third node N3, and second terminal connected to a fourth node N4 for introducing current according to the potential at a second voltage supply node N8, the transistor M7 having a specific value for a threshold value representing the size of voltage supplied to the control terminal to conduct a current of a specific amount between the first terminal and the second terminal; and a transistor M5 with a control terminal connected to fourth node N4, first terminal supplied with a first voltage, and a second terminal connected to a second node N2, the threshold value of transistor M5 being smaller than the specific value.