Current Clamp Circuit Parasitic Resistance Compensation
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Solution Overview
Problem
Conventional current clamp circuits fail to accurately sense the current of the output signal due to unequal parasitic resistances in MOSFETs, leading to inaccurate bias signal generation and potential over-heating of load circuits.
Innovation Solution
A current clamp circuit that includes a current-source circuit, a current-sense circuit with a multiplexer circuit and operational amplifier, and a feedback circuit, which modifies the resistance of a resistive network using control signals to compensate for parasitic resistances and accurately sense the output current, preventing over-heating by limiting the current to a threshold level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a compensation resistor is connected between the source of the second MOSFET and the op-amp to equalize voltage drops, then the voltage drops across parasitic resistors are approximately equal, but the resistance of the compensation resistor is fixed while parasitic resistors change due to PVT variations and package stress, resulting in inaccurate current sensing
Solution Approach 1:
The patent applies the dynamics principle by making the compensation resistor dynamic rather than fixed. The compensation resistor's resistance value is adjusted based on PVT variations and package stress conditions, allowing it to adapt to changing parasitic resistance values. This dynamic adjustment mechanism enables the compensation resistor to maintain accurate current sensing across different operating conditions, directly resolving the contradiction between measurement precision and adaptability.
2Measurement precision
If the resistance of parasitic resistors is reduced to minimize voltage drop errors, then the voltage drops become smaller, but the resistors become even more difficult to measure and rectify due to their already small resistance values in the range of a few milliohms
Solution Approach 1:
The patent applies the intermediary principle by introducing a compensation resistor as a mediator between the parasitic resistors and the measurement system. This compensation resistor is designed with a larger, more measurable resistance value that can be easily characterized and adjusted. By using this intermediary element, the system can indirectly compensate for the difficult-to-measure parasitic resistors without requiring direct measurement of their small resistance values, thus resolving the contradiction between measurement precision and measurement difficulty.
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 proposed solution accurately senses the output current and prevents over-heating by dynamically adjusting resistances to match voltage drops, ensuring the current remains below the threshold, thus protecting the load circuit from damage.
Implementation Method 1
The current-sense circuit includes a second MOSFET and an operational amplifier (op-amp) in a negative-feedback configuration
Implementation Method 2
The multiplexer circuit modifies a resistance of the resistive network based on a first control signal
Implementation Method 3
The feedback circuit is connected to the current-source and current-sense circuits and generates the bias signal based on the sensed current signal
Data Source
AI summary
A current clamp circuit includes a current-source circuit, a current-sense circuit, and a feedback circuit. The current-sense circuit includes a transistor, a resistive network, and a multiplexer. The transistor outputs a sensed current signal having a current that is equal to a current of an output signal provided by the current-source circuit. The feedback circuit limits the current of the sensed current signal and the output signal below a threshold current. The multiplexer modifies a resistance of the resistive network based on a first control signal. The multiplexer circuit and the feedback circuit are programmed using the first control signal and a second control signal when the transistor operates in a linear region and in a saturation region, respectively, to accurately output the sensed current signal.