Smart analogue

02 September 2015

The world of industrial automation is entering the fourth industrial revolution.

A paradigm shift in which rising awareness of energy efficiency, environmental concerns and regulations, qualitative productivity and operational health and safety, contribute to the continued growth of machine to machine (M2M) technology. “Smart production” will become a norm in the manufacturing engineering sector, where intelligent machine systems, through networks interconnectivity will be capable of managing industrial production processes independently from human intervention, thereby making the “Internet of Things” a reality.

The M2M communications are made possible with the use of industrial instrumentation comprising of intelligent sensors capable of capturing events and relaying the data over a network to an application that translates the captured event into meaningful information that can be analysed and acted upon.

Looking closer into the intelligent sensor system structure, the sensors (or transducers) are connected to one or more microcontroller unit (MCUs) that are at the core of embedded systems. The sensor’s output goes to the MCU’s input. The MCU processes that incoming signal and executes control functions accordingly. Depending on the application and situation, the sensor’s signal might cause the MCU to execute tasks predefined by the user. When used together and properly interfaced, these components function as "detect and control" electronics, enabling greater functionality, convenience, safety and efficiency in embedded sensor systems.

However the transducers’ output signal generated may be very weak, in a noisy environment, or delivered in a format incompatible with the one required by the MCU. Almost all MCUs have built-in analogue-to-digital converter functions (ADCs or A/Ds) for translating analogue sensor signals into a digital format. Those ADCs have restricted capabilities; for instance, they generally accept only a limited range of input voltages. To boost these signals to the level required by the MCU, or perform the necessary bridging (adaptation) function to implement signal compatibility between the transducer and the MCU, an Analogue Front End (AFE) is necessary. Furthermore, the transducers’ output may contain too many unwanted frequencies. This noise must be removed before the analogue signal is converted to digital. The AFE solution employs low-pass filter circuitry to block out high-frequency noise and/or high-pass filter circuits to remove lower-frequency noise.

Engineers in the fast developing industry are looking for solutions enabling them to reduce the development time of their analogue circuit, and release their products faster to the market. To answer the needs, a new type of AFE design approach was needed, which is easy to apply, flexible, quick and effective.

Renesas’ R&D labs have finalised proprietary Smart Analogue circuitry and development tools that can significantly reduce the time and effort to develop new AFEs. Using the programming side from the MCU, Smart Analogue makes use of the MCU to control the design of analogue circuits, adjust its structure and its characteristics into a sensor application.

Smart Analogue circuits are designed at a computer screen using configurable designed operational amplifier circuits that greatly reduces the design time.

As a sensor equipped system uses different type of transducers, for many different purposes, each of these sensors must have its own analogue circuit. Renesas Electronics therefore designed a platform that enables the user to design the most basic analogue circuit to the more advanced Op-amp based topologies, by selecting and combining appropriate types of Op-amp. 

The AFE engineer is able to get his development projects up and running quickly and easily, with the powerful GUI-based sensor configuration software tool that enables “on the fly”, i.e. while system is operating, configuration and simulation of the analogue front-end. The designer can easily, via simple mouse operation at the screen of a personal computer or work station, select the wiring and connections between the analogue blocks, change gain values or do offset tuning, and adjust other parameters. This greatly simplifies sensors calibration or debugging and can reduce the overall design lead time between 3 to 8 months, significantly lowering development costs.

The chip can be custom-configured to implement a range of signal amplification gains and it provides an adjustable span of signal voltage offsets (see Figure 1). Additionally, the single-channel general-purpose amp in the AFE can be configured to implement a single-channel high-impedance instrumentation amplifier. This type of differential amplifier is essential for interfacing to high-impedance sensors such as piezoelectric types (see Figure 2).

Other elements found in the Smart Analogue blocks portfolio are single-channel amp (with sync detection), single-channel low-pass/high-pass filter with variable cutoff frequency, high precision 16 or 24-bit Delta-sigma A/D converter with built-in AUTOSCAN sequencer and programmable gain instrumentation amplification.

Compared to the classical discrete approach, component count can be reduced by a factor of ten, allowing for a much smaller overall footprint. Additionally, the power-on/off feature of each block of Smart Analogue subsystem yields significant savings in power consumption, in some cases as much as 20 per cent.

The Smart Analogue platform approach is particularly versatile and convenient. It can be implemented in two ways. One method based on a Smart Analogue IC, which is a single-chip silicon die implementation of an AFE. System engineers insert it into the embedded control system to connect the transducer to the MCU. The other one applies a Smart Analogue MCU, a device that combines both AFE and MCU chips into a single, integrated package. 

The Smart Analogue MCU combines a Smart Analogue IC and an MCU into a space-saving, single-package device simplifying the design of sensor-based embedded control systems. Its internal MCU can be used to optimise the sensor compatibility of the AFE chip, as well as to control that chip’s signal-interfacing characteristics. Due to this unique combination of capabilities, the Smart Analogue MCU is the only AFE solution that can handle the different outputs from diverse types of voltage, current and differential-output sensors. It provides enough connection terminals to accommodate all the sensors typically needed, eliminating the traditional requirement to have a separate AFE circuit for each sensor. The Smart Analogue MCU helps shrink the circuit board, while simultaneously decreasing system component counts and costs.

The reconfigurable characteristics of Smart Analogue, means that engineers now have a field programmable solution which can be used to plan sensor sensitivity loss over time. Existing AFE design approaches make it necessary during the manufacturing process to perform manual trimming to compensate for variations in sensor characteristics. By contrast, a Smart Analogue MCU automates this process with the implementation of automatic self-correction features. Thereby cutting system production and commissioning costs, while increasing the sensor-based system’s operating lifetime.

Using the new Smart Analogue solutions, engineers can readily select the configuration and main features of the AFE they require and, thereafter, change those selections as often as necessary. This flexible design capability significantly reduces the time that otherwise would be necessary for component selection, board design, and parts procurement. 

Smart Analogue technology represents a new innovative platform for AFE design contributing to the implementation of enhanced features into intelligent sensors, with the added values of downsized systems, shortened design cycle and lowered system cost. By saving cost and time, the new customisable semiconductor devices enable sensor manufacturers to create products that otherwise might be too expensive to produce or take too long to bring to market.

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