Current Sense Circuit for PWM Driver Using Shared ADC
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Solution Overview
Problem
Traditional ABS and ESP systems require multiple current sense amplifiers for each valve actuation circuit, leading to wasteful current consumption and unnecessary die space due to separate high and low-side sense amplifiers and ADC sigma delta converters.
Innovation Solution
A current sensing circuit for PWM drivers that includes a PWM control circuit with a first and second switching device, an ADC comprising a DAC, comparator, and successive approximation register, which tracks and accurately measures current through a PWM driver using an external resistor for bias generation, reducing the need for multiple sense amplifiers and optimizing die area and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate high-side and low-side current sense amplifiers are used for each valve actuation circuit, then current measurement accuracy is maintained, but current consumption and die space increase significantly
Solution Approach 1:
The patent combines multiple current sense amplifiers into a single shared amplifier that serves both high-side and low-side valve actuation circuits. The amplifier is configured to measure currents from multiple circuits sequentially or simultaneously through multiplexing techniques, eliminating the need for separate amplifiers for each circuit while maintaining measurement accuracy through proper timing and signal conditioning.
Solution Approach 2:
The current sense amplifier is designed as a universal component that can measure currents from multiple different valve actuation circuits. The amplifier incorporates multiplexers and switching mechanisms that allow it to connect to and measure currents from any of the valve circuits, making a single amplifier perform the function of multiple dedicated amplifiers.
2Measurement precision
If separate high-side and low-side current sense amplifiers are used for each valve actuation circuit, then current measurement capability is ensured, but die space requirements increase
Solution Approach 1:
The patent merges multiple current sense amplifier circuits into a single integrated amplifier unit. By combining the differential input stages, operational amplifiers, and output stages into one shared component, the die space required is reduced from the sum of multiple separate amplifiers to approximately one amplifier's footprint, plus minimal additional space for multiplexing circuitry.
Solution Approach 2:
The patent introduces time as an additional dimension for current measurement. Instead of requiring spatial separation of amplifiers for simultaneous measurement of multiple circuits, the system measures currents from different circuits at different time intervals within each PWM period. This temporal multiplexing approach allows accurate current sensing across multiple circuits without proportionally increasing die space.
3Measurement precision
If ADC sigma delta converters are implemented for each valve actuation circuit, then current conversion accuracy is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent consolidates multiple ADC sigma delta converters into a single shared converter unit. The ADC is time-multiplexed to convert current signals from multiple valve actuation circuits sequentially. By sharing the complex sigma delta modulation and conversion hardware among multiple circuits, the device complexity is dramatically reduced while maintaining conversion accuracy through proper timing synchronization with the PWM control signals.
4Reliability
If multiple current sense amplifiers are used in traditional ABS and ESP systems, then reliable current sensing is achieved, but power consumption becomes wasteful
Solution Approach 1:
The patent merges multiple independent current sense amplifier functions into a single multi-functional amplifier that serves multiple valve actuation circuits. This consolidation maintains reliable current sensing for all circuits while eliminating the redundant power consumption associated with running multiple separate amplifier circuits, achieving both reliability and energy efficiency.
Data Source
AI summary
A current sense circuit for a PWM driver comprises: a PWM control circuit comprising: a first switching device arranged to receive a PWM signal from the PWM driver whose current is to be sensed; and a second switching device whose supply current is arranged to track the sensed current of the PWM driver. An ADC is operably coupled to the first and second switching device. The ADC comprises: a DAC arranged to provide a current sense to the second switching device that tracks the current passing through the PWM driver; a first comparator arranged to receive and compare an output current from the DAC and an output current from the first switching device; and a first successive approximation register arranged to receive an output from the comparator and provide: a first output to the ADC; and a second output that provides a representation of the sensed current.