Current Sensor Impedance Compensation for PVT-Accurate Sensing
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Solution Overview
Problem
Current sensing in SoCs is compromised by variations in resistance of power switches due to PVT changes, leading to inaccurate current measurements.
Innovation Solution
A current-sensing circuit with a replica switch and multiplexer implements time-interleaved impedance compensation, generating a compensation factor to correct for resistance variations in power switches, using a switched-capacitor amplifier with autozeroing to enhance accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current-sensing circuit is implemented without impedance compensation, then the device complexity is reduced, but the measurement precision deteriorates due to PVT-induced resistance variations
Solution Approach 1:
The patent employs a replica switch that copies the electrical characteristics of the power switch, including its PVT-induced resistance variations. By measuring the voltage across the replica switch with a known current, the circuit obtains a copy of the impedance variation pattern, which is then used to compensate the current measurement through division, eliminating the need for complex calibration while maintaining high precision
Solution Approach 2:
The patent introduces an intermediary compensation mechanism using the replica switch and multiplexer system. The replica switch acts as a mediator that translates the power switch's impedance variations into measurable voltage signals, which are then processed through the multiplexer and divider circuit to generate correction factors that improve measurement accuracy without requiring direct modification of the power switch itself
2Measurement precision
If a replica switch and multiplexer are added for impedance compensation, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The multiplexer in the patent serves multiple functions: it selectively connects either the power switch or the replica switch to the amplifier input, enabling both the measurement of actual current and the characterization of impedance variations through a single unified circuit path. This multi-functionality reduces the need for separate dedicated circuits for each measurement mode
Solution Approach 2:
The patent utilizes parameter changes in the replica switch's resistance as a function of PVT conditions to track and compensate for impedance variations. By monitoring how the replica switch's resistance parameter changes under different process, voltage, and temperature conditions, the system dynamically adjusts the current measurement through division, converting a source of error into a compensation mechanism
3Measurement precision
If time-interleaved measurement of power switch and replica switch is implemented, then the measurement precision improves through compensation, but the measurement time increases
Solution Approach 1:
The patent implements periodic time-interleaved measurement cycles where the multiplexer alternates between connecting the power switch and the replica switch to the amplifier. This periodic switching enables the system to collect both the actual current measurement and the impedance variation data in an organized sequence, allowing for systematic compensation calculations that improve precision while maintaining predictable timing
Solution Approach 2:
The patent performs preliminary measurement of the replica switch's voltage to characterize impedance variations before using this information to correct the power switch current measurement. By obtaining the impedance profile data in advance through the time-interleaved sequence, the system can apply the appropriate compensation factor to the main current measurement, improving accuracy without requiring real-time complex calculations
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 solution provides accurate current estimation by compensating for resistance changes in power switches, improving current management and reducing errors in SoC operations.
Implementation Method 1
using a switched-capacitor amplifier with autozeroing to enhance accuracy
Data Source
AI summary
A system includes one or more power switches, a replica switch, a current source coupled in series with the replica switch, and a multiplexer having a first input, a second input, a third input, a fourth input, a first output, and a second output, wherein the one or more power switches are coupled between the first input and the second input of the multiplexer, and the replica switch is coupled between the third input and the fourth input of the multiplexer. The system also includes an amplifying circuit having a first input, a second input, and an output, wherein the first input of the amplifying circuit is coupled to the first output of the multiplexer, and the second input of the amplifying circuit is coupled to the second output of the multiplexer. The system also includes an analog-to-digital converter (ADC) coupled to the output of the amplifying circuit.