IN Brief:
- The integrated shunt-based current sensor operates with common-mode voltages up to 60V.
- DLL-assisted dynamic body biasing addresses distortion created by body effects in high-voltage transistors.
- The 0.18µm BCD implementation rejects PWM common-mode interference at switching frequencies up to 2MHz.
Delft University of Technology researchers have demonstrated a fully integrated shunt-based current sensor that operates with common-mode voltages up to 60V while rejecting high-speed PWM interference at switching frequencies reaching 2MHz.
The design targets current measurement in high-voltage switched power systems, where a relatively small differential voltage across a shunt resistor must be measured accurately while both input terminals move rapidly with the converter or driver switching waveform.
That creates a difficult analogue front-end problem. The signal representing load or phase current can be small, yet it may sit on a common-mode waveform tens of volts higher and subject to very high dV/dt. Errors introduced by those switching transitions can overwhelm the useful signal if the sensing amplifier cannot recover quickly enough.
Floating current-sensing architectures offer one way to handle the voltage range because the input stage can move with the common-mode voltage. Higher-voltage transistor structures introduce another problem, however: substrate and body effects can change device behaviour as the common-mode level moves, degrading linearity across the operating range.
The Delft design addresses that distortion using delay-locked-loop-assisted dynamic body biasing. The circuit actively adjusts body conditions in the high-voltage input devices rather than allowing them to vary uncontrolled with the switching waveform, improving the consistency of the analogue front end through the PWM cycle.
The sensor was fabricated in a 0.18µm BCD process. BCD technologies combine conventional analogue and digital circuitry with devices capable of operating at higher voltages, making them well suited to power-management ICs where control, sensing, and high-voltage interfaces need to sit on the same die.
Measurements from the implementation show improvements of up to 31dB in second-harmonic distortion and 14dB in total harmonic distortion plus noise when the dynamic body-bias technique is used. The underlying work also reports peak THD+N of -82.3dB while maintaining operation with common-mode voltages to 60V.
PWM rejection remains critical because the sensor is intended to operate in switching environments rather than on a static high-voltage rail. The design rejects common-mode interference at frequencies up to 2MHz, extending its usefulness towards power stages where faster switching is being used to increase control bandwidth or reduce passive-component size.
Higher switching frequency is attractive in motor drives, audio amplifiers, and power converters, but it leaves less time for the current-sensing front end to settle after each transition. A measurement circuit that requires a long recovery period may provide only a narrow useful sampling interval before the next switching edge arrives.
Fast edges also couple through device capacitances, PCB parasitics, packages, and isolation structures. The resulting transient can be much larger than the shunt voltage being measured, so effective current sensing depends on dynamic common-mode immunity rather than headline voltage rating alone.
Accurate current information feeds several functions in modern power electronics. Motor-control systems use it for torque and phase control, converters use it for regulation and protection, while power amplifiers can use current monitoring for load protection and fault detection. A measurement error caused by PWM switching can therefore propagate directly into the control loop.
The body-bias technique is particularly useful because it addresses analogue linearity rather than simply protecting the circuit from high voltage. Distortion matters when the current signal is used for precision regulation or threshold detection, and an apparently small systematic error can become significant once it feeds a closed-loop controller.
The research implementation is not yet a commercial sensor product. A production IC would still have to demonstrate behaviour across temperature, process variation, package parasitics, calibration, shunt selection, electromagnetic interference, and qualification requirements appropriate to the intended application.
The underlying measurement problem is nevertheless becoming more demanding as wide-bandgap switches and faster control architectures push edge rates and PWM frequencies upwards. Measuring a small current-derived voltage accurately while the surrounding circuit moves through tens of volts at high speed is increasingly a defining analogue challenge inside modern power electronics.
