Source-Follower Output Circuit With Intermediate Gate 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 the application of power supply voltage between the gate and source, leading to increased device area and standby current.
Innovation Solution
A semiconductor output circuit design that uses an intermediate voltage generating circuit and inverter to apply a voltage based on the intermediate potential to the gate of the depletion transistor, allowing the depletion transistor to be turned on or off within a voltage range smaller than the battery voltage level, enabling the use of a device with lower breakdown voltage.
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 be turned on or off, but a higher breakdown voltage transistor is required leading to increased device area
Solution Approach 1:
An intermediate voltage generating circuit is introduced as a mediator between the power supply and the depletion transistor gate. This circuit generates an intermediate voltage that is lower than the full power supply voltage, applying it to the gate of the depletion transistor. This intermediary voltage level allows the depletion transistor to function as a shutdown device while requiring a lower breakdown voltage, thereby reducing the device area.
2Loss of energy
If a depletion transistor is used as a shutdown transistor, then standby current can be limited without a bias resistor, but a higher breakdown voltage transistor is required
Solution Approach 1:
The voltage parameter applied to the depletion transistor gate is changed from the full power supply voltage to an intermediate voltage level. This parameter change is achieved through the intermediate voltage generating circuit which outputs a voltage lower than the power supply voltage. By changing the voltage parameter, the depletion transistor can maintain its low standby current characteristic while requiring a lower breakdown voltage.
3Strength
If a higher breakdown voltage transistor is used, then the depletion transistor can handle power supply voltage, but the device area increases
Solution Approach 1:
The intermediate voltage generating circuit acts as an intermediary that reduces the voltage stress on the depletion transistor. Instead of applying the full power supply voltage to the gate, the circuit generates and applies an intermediate voltage level. This allows the use of a depletion transistor with lower breakdown voltage capability, thereby reducing the required transistor area while still achieving effective shutdown function.
Data Source
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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.