With so many new monolithic data converters announced every month, it's easy to forget that hybrids still dominate certain markets. For instance, Datel's ADS-953 subranging 18-bit analog-to-digital converter (ADC) achieves a 1-Msample/s rate. But that performance comes at a price.
In lots of 100, the commercial temperature-range version of the hybrid costs $464 each. The military temperature-range version costs $562. That's roughly 20 times the cost of an 18-bit, 800-ksample/s or a 16-bit, 1-Msample/s monolithic device. Obviously, Datel has crafted a specialized component.
Product marketing manager Bob Leonard says the combination of extra resolution and conversion rate is vital to certain customers. Resolution, for example, can spell the difference between a soldier making a positive identification in a night scope and a tragic friendly-fire incident. In magnetic-resonance imaging systems, faster sampling applied across multiple channels translates to faster diagnoses, and perhaps more importantly to claustrophobic patients, less time in the MRI tunnel.
Leonard also says that design engineers for relatively low-volume applications, such as weapons systems and high-end medical devices, are willing to trade off bill-of-material (BOM) costs for nonrecurring engineering (NRE). As good as today's monolithic devices are, he says, making them work in-circuit requires some art.
The hybrids contain all the other components needed, so they're board-ready. For the ADS-923, that means a fast-settling sample-and-hold amplifier, the subranging (two-pass) ADC itself, an internal reference, timing/control logic, and error-correction circuitry.
The ADS-923 ADC typically dissipates 1.45 W, running from separate ±15-V and ±5-V supplies. Worst-case signal-to-noise ratio and SINAD (across the industrial temperature range to 100 kHz) are 91 and 76 dB, respectively. Worst-case aperture-delay is 20 ns. Typical sample-and-hold acquisition time to ±0.003% of full-scale for a 10-V step is 260 ns.