Programmable analog technology is beginning to get traction among systems designers in various industrial, medical, and communications applications. Like the digital FPGA, programmable analog can be used to implement a wide range of functions. In the analog domain, these include front-end sensor conditioning, complex analog filtering, analog control loops, and other types of analog processing.
Traditionally, sensor signal conditioning circuitry has been designed using discrete components such as op amps, resistors, and capacitors. Sometimes analog multiplexers, digital potentiometers, or special analog functional devices are used. Although designing with discrete devices is probably the norm for many analog designers, it is prone to error and susceptible to component tolerances and drifts. Also, because the analog circuitry is usually the least documented part of the design, it will require significant redesign if upgraded or modified. The traditional analog approach also makes the front-end design very specific to the system, requiring redesign even if slightly different versions of the boards are needed. This can also create huge manufacturing headaches.
Programmable analog is uniquely able to shorten the design and development cycle for analog sensor conditioning. By allowing the abstraction of analog functionality in software, programmable analog components permit circuit parameters to be tweaked and circuit topologies to be modified within the development software environment. Some of the newer programmable silicon platforms also allow nonlinear functions, like user-defined transfer functions, to be implemented using an on-chip lookup table. With programmable analog, the conditioning circuit can compensate for sensor degradation over time and operating conditions.
Also, the engineers can take a platform approach when designing and supporting multiple variants of the same system board. Instead of managing multiple designs, each with its own bill of materials, the engineer can differentiate the designs using a different configuration file implemented on the same system board.
Programmable analog technology may not be suitable for all types of sensor conditioning. Some sensors produce very low voltages that must be amplified by a low-noise amplifier. Or, minimizing power consumption or cost may be the absolute priority. In these cases, a programmable analog device is not likely to compare favorably against a well designed low-power or a low-cost discrete design. However, for most industrial and medical sensor applications, a design based on a programmable analog technology is probably better suited for circuit tweaking, ease in maintaining multiple manufacturing lines, and potential field calibration.
Today's programmable analog solutions can implement complex filters with guaranteed parameters that can be updated by the system processor on-the-fly. Users can thereby compress the normally time-consuming, trial-and-error filter implementation process into a matter of minutes rather than weeks.
Some partially programmable filters have been available as standard products, but fully programmable analog devices provide truly exceptional flexibility. All types of filters and common filter approximations can now be implemented on the same silicon fabric. The implemented filter is completely under the control of the processor: Filter parameters can be swept, and the filter type and order can be changed on-the-fly. Programmable analog architectures based on switched-capacitor technology provide very accurate filter implementation because the filter parameters depend on the ratio of two capacitors, which tracks with 0.1% precision.
The advent of the programmable analog technology makes various flexible circuits possible with levels of precision and drift that could previously be achieved (if at all) using only specialized devices or in the digital domain. As this technology becomes more mainstream, it promises to significantly impact the way we view analog design and the capability of the analog subsystem on the board.
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