Integrated Circuit Current Regulation with On-Chip Measurement Resistor
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Solution Overview
Problem
Existing integrated circuit arrangements for current regulation of electromagnetic loads face challenges in accurately measuring coil current due to small voltage drops and large common mode jumps, particularly in battery charging systems, where manufacturing variations and temperature dependencies complicate precise current measurement.
Innovation Solution
Incorporating an on-chip measurement resistor with digital processing means for offset correction and temperature compensation, along with a full differential measurement amplifier, sample-and-hold circuit, and low-pass filter, to improve accuracy and reliability of current measurement during the freewheeling phase, and using a temperature sensor for real-time adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external or internal measurement resistor (shunt) is used to measure coil current, then current measurement can be performed, but the small voltage drop on the shunt and large common mode jumps on the amplifier input prevent satisfactory operation
Solution Approach 1:
The patent introduces an intermediary measurement system that converts the difficult-to-measure small voltage drop into an easily measurable frequency signal. The measurement resistor is integrated into an oscillator circuit where the voltage drop modulates the oscillation frequency, allowing current measurement through frequency detection rather than direct voltage measurement, thus avoiding the common mode jump problem
Solution Approach 2:
The patent replaces the traditional voltage-based measurement system with a frequency-based measurement system. Instead of using a voltage amplifier to detect the small voltage drop, the system uses an oscillator where the voltage drop controls the frequency, and a frequency counter measures the frequency. This substitution of measurement domain (from voltage to frequency) eliminates the harmful effects of small voltage drops and large common mode jumps
2Measurement precision
If digital processing means are added for compensation of manufacturing variations and temperature influences, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-characterizing the measurement resistor during manufacturing. The actual resistance value is measured and stored as a correction factor before the device is deployed. During operation, this pre-stored correction factor is used to compensate for manufacturing variations, eliminating the need for complex real-time calibration circuits
Solution Approach 2:
The patent implements feedback through temperature compensation where the temperature-dependent behavior of the measurement resistor is predicted using stored correction data. The digital processing means uses the measured temperature and stored correction factors to calculate and apply compensation, creating a closed-loop system that maintains accuracy without requiring complex hardware
3Measurement precision
If measurement is performed during freewheeling phase only with sample-and-hold circuit, then accurate current measurement is achieved, but productivity is reduced due to limited measurement opportunities
Solution Approach 1:
The patent uses periodic action by measuring the current only during the freewheeling phase of the electromagnetic load operation. The sample-and-hold circuit captures the voltage drop during this specific periodic window when the switch is open and current flows through the measurement resistor. This periodic measurement approach ensures accuracy while accepting that not all time periods are used for measurement
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 enables accurate and reliable current measurement under various operating conditions, effectively compensating for manufacturing variations and temperature influences, thereby enhancing the precision and stability of current regulation in battery charging systems.
Implementation Method 1
an on-chip measurement resistor (5) for measuring the coil current (3) in the freewheeling path of the control circuit
Implementation Method 2
a temperature sensor is assigned at least indirectly to the measurement resistor, whose temperature measurement signal is fed to the digital processing means for temperature compensation of the voltage signal
Implementation Method 3
the output of the sample-and-hold circuit is connected to the input of a low-pass filter
Data Source
AI summary
An integrated circuit arrangement for current regulation of an electromagnetic load, especially an electric motor, generator, solenoid valve, or the like, with a coil, a power switch element, and a freewheeling diode is disclosed. In one embodiment, the circuit arrangement has an integrated measurement resistor for measuring the coil current. The measurement resistor is arranged in a freewheeling path of the circuit arrangement in series between the freewheeling diode and the power switch element, and has a digital processing means connected after a voltage measurement device assigned to the measurement resistor for at least partial compensation of resistor manufacturing variations and/or temperature fluctuations in the voltage signal and/or an error due to analog voltage signal processing.