Analog Isolated Multilevel Quantizer for Voltage Sensing while Maintaining Galvanic Isolation

TL;DR

The paper tackles high-voltage isolated voltage sensing by addressing the power, EMI, and complexity drawbacks of conventional isolation amplifiers. It introduces the Analog Isolated Multilevel Quantizer (AIMQ), which uses a Zener diode ladder and one-hot encoded optocoupler outputs to convey discrete voltage levels across an isolation barrier without a primary-side converter. Through SPICE simulations and a complete PCB-model, the authors show that 8-level (3-bit) telemetry can track bus voltage with reduced primary-side power, and provide an efficiency comparison that in a representative case yields a power ratio of about $\frac{P_{tot2}}{P_{tot1}} \approx \frac{1}{10.1}$. The work also outlines a practical implementation with a parent/daughter board design, discusses bandgap references, and argues that AIMQ can be scaled to higher bit-depth as optocoupler CTR and packaging improve, making isolated voltage sensing more compact and EMI-friendly.

Abstract

A low-power, compact device for performing measurements in electrical systems with isolated voltage domains is proposed. Isolated measurements are required in numerous applications. For instance, a measurement of the bus voltage for a system with a high supply voltage and lower isolated local voltage level may be needed for system health monitoring and control. Such a requirement may necessitate the use of isolation amplifiers to provide voltage telemetry for the local system. Isolation amplifiers require dual galvanically isolated supplies and use magnetic, capacitive, or optical barriers between primary and secondary sides. Producing this supplemental voltage requires an extra voltage converter, which consumes power and generates electromagnetic interference which must, in turn, be filtered. Complex designs incorporating feedback are needed to achieve linear response. The proposed Analog Isolated Multilevel Quantizer (AIMQ) addresses these issues by monitoring the primary-side signal and communicating the results to the secondary side using a novel scheme involving Zener diodes, optocouplers, transistors, one-hot coding, and discrete outputs. The result is a low power isolated transducer that can in principle be extended to an arbitrary bit depth.

Figures (12)

• Figure 1: Convoluted power scheme required for isolation amplifier primary-side power. The jagged line represents the magnetic barrier.
• Figure 2: Block Diagram of Analog to Digital Converter
• Figure 3: Functional Unit of the AIMQ. This circuit will output a scaled secondary-side signal $V_{out}$ when the primary-side voltage exceeds 136 V.
• Figure 4: Turnoff mechanism to disable all lower voltage channels and implement the one-hot encoding scheme. The Level 7 channel is shown.
• Figure 5: The Level 6 channel in this case corresponds to an input voltage greater than 116 V due to the breakdown voltages of D15 and D18.