Traditional solid-state electricity meter architectures dating as far back as the late 1980s combined multiple ICs to assemble a functional set capable of measurement and display of electric power consumption. In a typical system, a microcontroller performed management and display tasks and multiple A/D converters combined with a fixed function signal processor performed metrology functions.

While this simple system partitioning offered some design flexibility, dependence on components which had not been optimised for metering applications required considerable software development and signal processing expertise. First examples of IC integration emerged when large meter manufacturers developed their own proprietary metrology ASIC integrating A/D conversion and DSP functions, but until recently integration had for the most part stopped there.

MULTI-CHIP VERSUS SOC

Significant changes and opportunities in the metering industry in recent years have imposed new challenges on manufacturers, which can only be met with new approaches on all technology fronts. Innovations in systems, sensors, packaging, software and electronics continue to offer new ways to improve the reliability and adaptability of meters to various markets. This in turn reduces cost and time to market – key requirements for global competitiveness.
In line with these trends, one innovative solution came when Teridian Semiconductor, a former TDK Group company and a 16-year veteran in metering IC development, produced a family of devices offering meter manufacturers a single platform which can adapt to multiple market requirements quickly and without compromise, based on its patented Single Converter Technology. The range of meters covered by this architecture includes everything from low cost single phase up to high performance three phase meters, all using one architecture and development platform – a total solution approach matched by no other IC supplier.

UNDER THE HOOD

At first glance, Teridian’s 71M651x meters appear to be a classic system on chip (SOC) integration exercise where essential components of the meter are integrated in one chip. Although this level of integration improves cost and reliability, it may fall short of addressing both time to market and the scalability requirements of the market, specifically when metrology is concerned. There are now some examples of low-end mixed signal micro-controllers that work well enough for one or two low-end residential meter designs, but fail to benefit design projects targeting several important market segments. By far the most distinguishing feature of the Teridian solution is its patented Single Converter Technology™. This architecture comprises only one 21-bit second order delta-sigma A/D converter with up to seven multiplexed analog inputs and a programmable Compute Engine (CE).

MI 4 2005 CS Figure 1

Figure 1 – VAR-HR accuracy, 0.3A to 200A, 240V

This revolutionary approach eliminates channel cross talk, one critical problem in precision metering, and achieves better than 10 PPM/°C performance accuracy over 2000:1 current range. This accuracy is maintained across the industrial temperature range using digital temperature compensation techniques.
In essence, nominal and high temperature voltage reference trim coefficients are hard coded in each specific metering device, which enables metrology functions to correct for errors based on temperature values measured via internal sensor. The same scheme can be extended to compensate for external current sensor temperature dependencies. At the heart of the 71M651x metrology subsystem is a 32-bit Compute Engine that packs all standard active and reactive power measurement functions and is upgradeable with new custom functions and adjustments as needed. Running independently of the internal 8-bit MCU core, the CE receives and processes sensor data from the 21-bit A/D converter with a very high dynamic range. The programmable nature of the CE and its soft approach to various configurations and characteristics of current sensors make it the ideal metrology platform for all meters.

FLEXIBILITY AND CONTROL

Leveraging the inherent flexibility of this architecture, many device and software variations now support active power, reactive power, RMS and other measurement functions with virtually any sensor including resistive shunt, current transformer, and Rogowski Coil as follows:

• 1 phase, 2 input basic residential & TOU meter
• 1 phase, 3 input residential meter with neutral current detection
• 2 phase, 4 input residential and dual/network meter
• 3 phase, 6 input, low cost polyphase meter
• 3 phase, 7 input low cost tamper proof meter
• 3 phase, 7 input high end commercial/industrial meter.

METERING IP AND PRODUCT DIFFERENTIATION

Clearly, meter designers need to leverage their know-how to differentiate their products in the market with advanced features. Adoption of purely standard off-theshelf products can seriously deplete this ability. To serve this key technical and business requirement, the programmable Compute Engine supports advanced signal processing development tools, and allows custom implementation of metrology algorithms, which can be stored in the secured FLASH memory. The ability to commit the entire firmware to mask ROM further protects each company’s IP and effectively allows for the same level of protection offered by custom ASIC solutions at a fraction of the cost.

MI 4 2005 CS Figure 2

Figure 2 – 71M6513 block diagram

MARKET ACCEPTANCE AT TIER 1 OEMS

To summarise, from the United States to Russia, South Africa to Europe, Teridian Semiconductor Corp. is beginning to see significant deployment of its Single Converter Technology™ at tier 1 OEMs around the world. When major meter manufacturers are charged with the challenging task of rapid and comprehensive upgrades of their metering programmes, they often face the conflict of reducing their bill of materials costs while also providing increased functionality. With Teridian's SOC solutions, major OEMs can focus on designing multiple products that meet the needs of the residential and industrial markets, while also having the flexibility of meeting those requirements with one platform.