Body-Connected FET Current Measurement via Voltage Control
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Solution Overview
Problem
Measuring effective current in field-effect transistors (FETs) is challenging due to the time required for the body to reach a steady-state condition, which is longer than the measurement time of standard instrumentation, and existing high-speed test equipment is expensive and not consistently accurate.
Innovation Solution
A semiconductor device comprising a first FET electrically coupled to a second FET of similar polarity, where the body voltage of the second FET controls the body voltage of the first FET, allowing for accurate measurement of effective current by averaging drain currents measured under different voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If standard instrumentation is used to measure FET effective current, then measurement precision is improved, but measurement time exceeds the body charging time, resulting in inaccurate readings
Solution Approach 1:
The patent applies preliminary action by pre-charging the body of the FET under test to a known voltage level before initiating the measurement process. This is achieved by connecting the body to a voltage source through a switch that is closed prior to measurement, ensuring the body reaches steady-state charge conditions before the actual current measurement begins. This eliminates the time delay issue by having the body already in the required state when measurement starts.
Solution Approach 2:
The patent uses an intermediary approach by introducing a separate body charging circuit as a mediator between the voltage source and the FET body. This intermediary circuit includes a switch and resistor network that controls the charging process independently from the main measurement circuitry, allowing the body to be pre-charged without interfering with the subsequent current measurement operations.
2Loss of time
If high-speed test equipment with fast sampling speed is used, then measurement time is reduced, but device complexity and cost increase significantly
Solution Approach 1:
The patent extracts the body charging function from the main measurement system and implements it as a separate, simple circuit module. By taking out the charging functionality and implementing it with basic components (switch, resistor, voltage source), the system avoids the need for complex high-speed test equipment while still achieving the required measurement speed through the simplified architecture.
Solution Approach 2:
The patent employs a simple, inexpensive body charging circuit using standard electronic components rather than relying on expensive high-speed test equipment. The charging circuit uses basic elements like switches, resistors, and voltage sources that are cost-effective and easy to implement, replacing the need for costly specialized instrumentation while maintaining measurement accuracy and speed.
3Measurement precision
If body charging time is extended to reach steady state, then measurement accuracy is improved, but productivity decreases due to longer measurement cycles
Solution Approach 1:
The patent applies preliminary action by completing the body charging process before the measurement cycle begins. The body is pre-charged to the required voltage level in advance, and once charged, the switch is opened to isolate the charging circuit from the measurement circuit. This separation allows the measurement to start immediately without waiting for charging to complete during the measurement cycle, thereby maintaining both accuracy and productivity.
Solution Approach 2:
The patent ensures continuity of useful action by maintaining the body at a stable charged state throughout the measurement process. Once the body is charged to the required voltage, the charging circuit is disconnected, and the body remains at this stable voltage during measurement. This continuous stable state allows for immediate and accurate measurement without repeated charging cycles, maintaining high measurement throughput.
Data Source
AI summary
A semiconductor includes: a first field-effect transistor (FET); and a second FET of similar polarity to the first FET, wherein a body of the first FET is electrically coupled to a body of the second FET, and a source of the first FET is electrically coupled to a source of the second FET, such that a body voltage of the second FET controls a body voltage of the first FET.