Source Follower Output Circuit Using Intermediate-Voltage Shutdown
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Solution Overview
Problem
Existing semiconductor output circuits using depletion transistors as shutdown transistors require transistors with higher breakdown voltage due to power supply voltage being applied between the gate and source, leading to unnecessary current flow and increased device area.
Innovation Solution
A semiconductor output circuit design that uses a depletion transistor as a shutdown transistor, where the voltage applied between the gate and source is controlled within a range smaller than the battery voltage level, allowing for the use of a device with lower breakdown voltage by generating an intermediate control voltage and creating an electrical short between the gate and source when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a depletion transistor is used as a shutdown transistor with power supply voltage applied between gate and source, then the transistor can effectively control the conductive state, but a higher breakdown voltage transistor is required leading to larger device area
Solution Approach 1:
The patent introduces an intermediate voltage generating circuit that creates a voltage level between the power supply voltage and ground potential. This intermediate voltage is applied to the gate of the depletion transistor during shutdown, serving as a mediator that reduces the voltage stress on the gate-source junction while maintaining effective shutdown control. The intermediate voltage acts as a buffer that protects the depletion transistor from full power supply voltage stress.
Solution Approach 2:
The patent changes the voltage parameter applied to the gate of the depletion transistor from full power supply voltage to an intermediate voltage level. By modifying this critical parameter, the breakdown voltage requirement for the depletion transistor is reduced, allowing the use of smaller devices with lower breakdown voltage ratings while maintaining shutdown functionality.
2Loss of energy
If a depletion transistor is used as shutdown transistor, then standby current can be limited without requiring a bias resistor, but higher breakdown voltage transistors with larger area are needed
Solution Approach 1:
The intermediate voltage generating circuit serves as an intermediary that enables the depletion transistor to achieve low standby current operation without requiring large device area. By providing a reduced voltage level at the gate, the circuit allows the use of smaller depletion transistors that would otherwise not have sufficient breakdown voltage margin, thus maintaining energy efficiency while reducing area.
Solution Approach 2:
The patent modifies the gate voltage parameter from full power supply voltage to an intermediate voltage level, which changes the operating conditions of the depletion transistor. This parameter change allows smaller devices to achieve the same low standby current performance, effectively decoupling the standby current reduction benefit from the large device area requirement.
3Ease of operation
If full power supply voltage is applied to the gate of depletion transistor, then effective shutdown control is achieved, but transistors with higher breakdown voltage and larger area are required
Solution Approach 1:
The intermediate voltage generating circuit acts as a mediator that simplifies the shutdown control operation by automatically providing the appropriate reduced voltage level to the depletion transistor gate. This intermediary circuit handles the voltage scaling, making the shutdown control easier to implement with smaller devices while maintaining effective control functionality.
Data Source
AI summary
Between a control terminal (gate) of an output transistor of a source follower configuration and an output terminal to which a load is coupled, a depletion transistor having a relatively lower breakdown voltage (that is, smaller device-area) is provided as a shutdown transistor of the output transistor, to thereby control a conductive state/nonconductive state of the depletion transistor. There are provided: the output transistor of the source follower configuration coupled between a first power supply line and the output terminal; the load coupled between the output terminal and a second power supply line; the depletion transistor coupled between the gate of the output transistor and the output terminal; and a control circuit controlling the conductive state/nonconductive state of the depletion transistor by applying, between a gate and a source thereof, a voltage smaller than a voltage deference between a potential of the first power supply line and a potential of the second power supply line.