One challenge in using delta-sigma analog-to-digital converters (ADCs) is that their input sampling currents can overwhelm high source impedances or low-bandwidth, micropower signal conditioning circuits. Last year, Linear Technology came up with an "Easy-Drive" family of delta-sigmas that addressed this problem by balancing the ADC's input currents (see the figure).
The latest member of this family, the 24-bit LTC2498, adds an eight-channel differential multiplexer ahead of the ADC. Its internal temperature sensor offers 1/30°C resolution and 2°C absolute accuracy. The ADC converts either the output of the temperature sensor or the input multiplexer.
After a new channel is selected, the LTC2498's delta-sigma filter settles in a single cycle. The LTC2498 communicates via an SPI-compatible serial interface and converts at up to 7.5 or 15 Hz while using the internal oscillator. It can be configured to reject 50-, 60-, or simultaneous 50/60-Hz line frequencies while maintaining 600-nVRMS noise across the full input voltage range.
A sister part, the LTC2496, offers 16-bit resolution. Both come in QFN-38 packages. Pricing is $3.45 for the LTC2498 and $2.65 for the LTC2496 in lots of 1000.
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