Maxim Integrated has recently introduced the MAX11300 (SPI interface) and MAX11301 (I2C interface) Programmable Mixed Signal I/O (PIXI™) Devices. They contain a 12-bit ADC, 12-bit DAC, 2.5V (0.24%) internal reference and temperature sensor and sport impressive specifications. These FPAAs (Field Programmable Analog Arrays) should be welcomed by the analog community, but it should be recognized that these devices are by no means the first FPAA products available and it might be argued that they are not the best available.
The PSoC family of products from Cypress Semiconductor has been available for a few years and the family continues to grow. The PSoC family includes products which have up to three ADCs (up to 20 bits), DACs, some op-amps, comparators, a voltage reference (0.1% accuracy), transimpedance amplifiers, capacitive sensing, LCD display drivers, and more. On top of all of this, they contain either an 80C51 or ARM processor, depending upon the PSoC variety. While the Maxim products carry a price tag of about $5.87, the PSoC family prices range from about $2.50 to just over $11.00, depending upon functionality. I would expect that the majority of applications could be satisfied with a PSoC that costs no more than the Maxim offering and the PSoC also has a CPU that the Maxim products do not.
The main drawback I see with the Cypress Semiconductor PSoC products is the fact that they contain so much that complete characterization and testing would be very costly, so specifications are minimal. The PSoC products have a lot of “typical” specifications, but only a handful of specifications with limits (min/max values).Yet, the presence of the CPU and the product price makes the PSoC a very viable option that should be considered. The PSoC products are certainly more versatile, but the MAX11300/01 have more complete and better specifications. The good news is that there is now more choice for those desiring an FPAA.
It is true of all programmable analog arrays that the resistance of the analog switches used to make the various connections can cause errors if they are not considered. The secret to obtaining good performance with these products is to be innovative when it comes to circuit topology. For example, avoid an analog switch in series with a gain setting resistor whenever possible. With a little thought concerning how you configure your circuit, you can obtain excellent performance with analog arrays.