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The Benefits of FPAA Technology for Implementing Analog Designs

by Suhel Dhanani
Sr. Product Marketing Manager
Anadigm

Analog design implementation has never been a science. In most cases, it remains an art that depends on the type, value, and tolerances of the components or silicon used for the implementation.

As a recent article put it, "the design of analog components has traditionally pivoted around low-level 'clever tricks' (art or black magic?) that involve transistor layout and parameter selection, thus making [it] virtually impossible to use higher level[s] of abstraction" (from The Art and Science of Integrated Systems Design by Alberto L. Sangiovanni-Vincentelli et al.).

Because of this, analog designers have missed out on the huge productivity gains brought to the digital realm by the abstraction in software of circuit designs to ever higher levels of functionality. There have been some attempts to introduce the analog equivalent of the FPGA, thus separating the design and implementation of analog designs and allowing for higher designer productivity. However, until now, there did not exist a cohesive analog programmable solution—stitching together the design software, the circuit abstraction blocks (I.P. modules), and the silicon platform to provide a comprehensive solution.

Required Elements of a Successful FPAA Technology

Like the digital FPGA technology that preceded it, the FPAA solution must incorporate the necessary aspects to allow for an easy design methodology and the implementation of the design in a pre-tested silicon platform.

A set of intuitive and easy-to-use design tools is the key to shortening the analog design cycle and allowing for the abstraction of the design into logical circuit blocks. The design tools must include not only the design software, but also a library of circuit abstraction modules that allow the designer to work at a higher level. For example, when a designer wants to implement an analog multiplier, the designer should be able to drop a multiplier block, specify the multiplication factor, and drop it in the circuit.

One of the more complex problems in analog design is the design and implementation of higher order analog filters. While some very good tools are available that allow the design of filters, the implementation aspect is tricky since the filter parameters are sensitive to the values, tolerances, and drifts of the passive components (resistors and capacitors) used for the implementation.

The latest FPAA solution, developed by Anadigm^®, is unique in this regard. It actually allows complex high-order filters to be both designed and implemented within minutes on an integrated, drift-free, and precise silicon platform. The filter tool (bundled in the software) allows the designer to specify the filter in terms of the filter characteristics, and then automatically uses the appropriate modules (called Configurable Analog Modules or CAMs) to implement the filter (Figure 1).

Figure 1 - Easy Design and Guaranteed Implementation of Complex Filters

The silicon platform of the FPAA solution must be versatile to accommodate a wide range of analog functionality, and must offer reliable, drift-free performance characteristics. There have been two approaches taken to developing FPAAs—the continuous-time and the switched-capacitor approaches—and each has its advantages. The switched-capacitor approach chosen allows for maximum versatility and lends itself well for implementation using CMOS technology. Switched-capacitor circuit designs are implemented using switches and capacitors. A resistor (which is required for any active filter circuit) is approximated by switched capacitors. It can also be shown mathematically that the transfer function does not depend on the values of these capacitances, but rather on the ratio of the values of the two capacitors. Thus, a silicon platform in which capacitor values are carefully matched makes the implemented design highly process- and temperature-independent.

Applications of the FPAA Technology

Analog signal conditioning and processing is used in a vast array of applications ranging from sensor interfaces to industrial controls, medical monitoring, seismic systems, and laser control. In most applications the analog signal conditioning is currently done with discrete components, analog ASSP/ASICs, or a DSP following digitization of the signal.

The new FPAA technology provides an elegant way of implementing these designs with the added benefit of reconfiguration. The key benefits of an FPAA over a fixed-function solution are:

a greatly simplified design process;
a one-component solution for multiple designs, greatly simplifying inventory management;
an integrated design solution—design specifications are immune to temperature, process, and component aging; and
precision operation and increased system reliability.

For example, the various functions performed by discrete components for conditioning a sensor signal can now be integrated in a single FPAA, as shown in Figure 2. Implementing this circuit in an FPAA allows the designer to carefully tune the circuit in software to account for the operating conditions and vendor-related variations. What's more, as sensors age, the system can be updated to adjust for this by merely updating the FPAA configuration bit-stream.

Figure 2 - All Sensor Signal-Conditioning Functions Can Be Integrated Within an FPAA

Extending the Application Space of FPAA Technology—Dynamic Reconfiguration

FPAAs offer users the capability to reconfigure the FPAA dynamically in a system. This new capability is derived from the innovative architecture of the Anadigmvortex FPAA that includes a "Shadow RAM" configuration memory, allowing the configuration data to be loaded into the FPAA while it is still operating (i.e., without powering down the device). With this functionality, the FPAA can now be modified on the fly by reloading new device configurations in real time.

This innovative feature takes FPAA application to another level, which is beyond the scope of this article. This is an area of massive untapped potential.

Conclusion

FPAA technology puts analog on an equal footing with digital in the design-automation revolution by providing an analog equivalent to the FPGA. For the first time, complex analog signal conditioning and processing functions can be integrated within an off-the-shelf, pre-tested device.

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