The evolution of integrated current sensors: A digital leap with the first Sigma-Delta bitstream output ICS

Integrated current sensors (ICSs) have steadily evolved since their earliest implementation. Their journey has been less about dramatic revolutions and more about incremental refinements: smaller form factors, improved accuracy, greater robustness in harsh environments, and stronger insulation for high-voltage applications.

What customers need most: four priorities driving ICS design

Every generation of ICS development has been guided by user needs. Market studies and direct customer engagement consistently highlight four priorities:

1. Performance over temperature ‘range’

   Accuracy across varying thermal conditions is critical. Drift and sensitivity offset can make or break performance, particularly in power electronics where conditions fluctuate rapidly.

2. Current-handling capability

   Smaller ICSs save board space and cost, but their integrated primary conductors typically limit continuous current capacity to around 30-50 amperes (A). Extending this range – without compromising performance or reliability – remains a central challenge.

3. Overcurrent detection

   Protection is essential in applications such as automotive, industrial automation, and renewable energy. Reliable over-current monitoring ensures safety and prevents costly system failures.

4. ‘Electrical’ Insulation

Both basic and reinforced insulation are necessary depending on the application. Effective insulation is critical for compliance and safety in high-voltage systems like electric vehicles and industrial drives.

Any new ICS must address these four fundamentals to succeed in the marketplace.

The path to miniaturization

The modern ICS story can be traced through several innovation milestones:

1. Closed-loop Hall effect ICSs

   These early designs used Hall effect sensing combined with custom application-specific integrated circuits (ASICs). They offered high accuracy and strong insulation but came at higher cost.

2. Open-loop ICSs

   Removing the feedback loop reduced complexity and cost, making current sensors more accessible for cost-sensitive markets. LEM’s HLSR Series embodied this breakthrough with a compact, PCB-mounted (printed circuit board) design that accelerated adoption.

3. The HMSR series

   Pushing further, LEM introduced the HMSR Series, a line of high-insulated ICSs balancing cost efficiency, accuracy, and miniaturization. Key features include:

   • Reinforced insulation for high-voltage applications
   • Low-resistance primaries to reduce power losses
   • Proprietary ASICs for precise signal conditioning
   • A miniature ferrite core for improved magnetic immunity
   • Integrated over-current detection

These analog HMSR sensors quickly became trusted components in both DC and AC applications where compactness, bandwidth (up to 300 kilohertz), and noise immunity were essential.

Figure 1: The miniaturization of current sensors. (Image source: LEM)

A digital shift: introducing the benefits of the HMSR DA

As industries undergo digital transformation, current sensing must evolve as well. With the launch of the HMSR DA Series, the first integrated current sensor with a Sigma-Delta bitstream output, LEM has taken a decisive step into the digital domain. This has profound implications for performance, design flexibility, and system integration across multiple industries.

Why Sigma-Delta modulation matters

A Sigma-Delta Modulator (SDM) converts an analog signal into a high-frequency, serial digital stream. For ICSs, this approach offers clear advantages:

1. Reduced quantization noise

   Unlike standard analog-to-digital converters, the SDM spreads noise across frequencies, allowing digital filters to extract a cleaner, high-resolution signal.

2. Predictable response time

   While a fixed delay (settling time) is introduced, it remains consistent and manageable.

3. Design flexibility

   Users can prioritize either high resolution (using higher-order filters) or faster response (with low-order filters).

4. Integration efficiency

SDMs fit seamlessly into complementary metal-oxide semiconductor (CMOS) processes, reducing system complexity and cost.

With a 10 megahertz (MHz) clock and an oversampling ratio of 128, the HMSR DA achieves a settling time of approximately 38.4 microseconds – fast enough for demanding applications while maintaining 11-13 bits of resolution.

System simplification

Traditionally, isolated digital current measurement required multiple parts: a shunt resistor, a digital isolator, and multiple power supply elements. This increases cost and the consumed PCB space exposes systems to noise vulnerabilities.

The HMSR DA replaces this entire assembly with a single compact sensor. Beyond consolidation, it also integrates ASIC-based intelligence and built-in over-current detection – capabilities conventional setups cannot easily replicate.

Flexible outputs for smarter design

The HMSR DA also introduces greater output flexibility:

1. Single-ended output

   Straightforward Sigma-Delta bitstream with clock

2. Differential output

This supports RS-422 and LVDS (Low-Voltage Differential Signaling) receivers, eliminating the need for external drivers. Differential signaling provides inverted outputs for both signal and clock, ensuring noise cancellation at high speed and low power.

This flexibility allows engineers to tailor systems for precision, response time, or maximum immunity depending on application requirements.

Where digital ICSs deliver the most value

Digital-output ICSs, like the HMSR DA, provide the biggest benefits in noisy environments where analog signals can degrade.

1. Robotics and servo drives

   Precise, noise-immune current measurement is critical for motor control.

2. CNC machine tools and textile machinery

   Compact, high-resolution sensors fit seamlessly into space-constrained systems.

3. Welding equipment and automated guided vehicles

   Applications that demand robust insulation and resilience against electrical disturbances benefit directly from digital signaling.

4. Automotive applications

As the automotive sector is rapidly electrifying, digital ICSs address long-standing challenges with noise and magnetic interference. From onboard chargers to traction inverters, digital signaling ensures cleaner, more reliable current measurement.

Looking ahead: what comes next for LEM’s digital ICs

The history of ICSs has always been defined by two forces: anticipating customer needs and advancing technology to meet them. While the adoption of digital ICSs is still in its early stages, the trend is clear. As industries push for smaller, cleaner, and more cost-efficient solutions, digital output will become a new standard.

The HMSR DA is the foundation of LEM’s digital sensor strategy – a breakthrough that unites Sigma-Delta bitstream output with proven insulation, compact packaging, and integrated protection features. This combination not only simplifies system design but also gives engineers the flexibility to prioritize precision, speed, or noise immunity based on their application requirements.

Today, the HMSR DA supports continuous currents of 30-36 A (35 A peak). Future generations will expand toward 100 A continuous, all while remaining PCB-mountable and compact. Looking further ahead, the planned elimination of the magnetic microcore will unlock faster frequency response and complete immunity to magnetic disturbances – removing one of the final limitations of analog design.

The HMSR DA is the first step of a digital roadmap that will redefine current sensing for the next decade and beyond.

Visit the DigiKey website for more information on how LEM is supporting the growing demand for smarter, more energy-efficient electronic solutions.