Maxim Integrated Products introduced the 8-channel MAX4539 and dual 4-channel MAX4540 calibration multiplexers. For calibration of precision A/D converters and for self-monitoring applications, each device includes precision resistive-dividers that include 15/4096 and 4081/4096 of the external reference voltage, accurate to 15 bits, and 1/2V+ and 5/8(V+ - V-), accurate to 8 bits.

MAX4539/MAX4540 multiplexers have enable inputs and address latching. When operating with 5V or ý5V supplies, all digital inputs have 0.8V/2.4V logic thresholds that ensure TTL and CMOS compatibility. All inputs have protection diodes that ensure ESD ratings higher than 2kV.

Both devices operate from a single supply in the range 2.7V to 12V, or from dual supplies in the range from ý2.7V to ý6V. (On resistances (100 ohm max) are matched to within 6 ohm max within a device, and each switch can handle rail-to-rail analog signals. The off leakage current is 0.1nA at TA = +25 ýC and 2nA at TA = +85 ýC.

These two parts plus others to come (MAX4578, higher voltage 8:1; MAX4579, higher voltage dual 4:1; MAX4598, selectable 8:1 or dual 4:1) represent a really nice family. Where you need to provide accurate ratios of a reference voltage and, for calibration, the reference itself -- and ground -- can be switched to the output. There are some differences in Maxim's literature for the first two parts as to whether the maximum on-resistance is 75 or 100 ohms, and whether matching is within 6 or 12 ohms, but either is acceptable for most tasks. I think too that the statement "accurate to 15 bits" would be more correctly put as "accurate to >14 bits."

These parts will find considerable use in calibration and monitoring systems in test equipment and complex data acquisition systems; they will also find considerable usage in signal routing systems, certainly over audio and such like frequency ranges; they could also lead to some interesting comparator applications in systems where signals need to be balanced out. Compared to other solutions that are possible the parts seem to be priced a little high. The parts are in production in 20-pin DIP, SO and SSOP and are priced at $2.84 for 1000-piece lots.