Once upon a time Atmel, of microcontroller fame, had a really interesting mixed-signal ASIC operation in France. A couple of years ago the powers that were at Atmel decided that ASICs were not a core business, and spun out the operation as e2v, which promptly became little-known in North America. This is unfortunate, because the company continues to thrive—now as a fabless ASIC house rather than a captive Atmel design shop—and has developed something of a specialty in testing the edge of the envelope in high-performance data converters. There's also an imaging product line and an extended-environment line of Freescale-licensed MCUs, for the record.

The term high performance in this case has two aspects, each relating to a division of e2v. On one hand, it could refer to high conversion speed. The Broadband Data Conversion group has recently announced what may be a record in ADC bandwidth: a configurable quad 10-bit, 1.25 Gsample/s converter. The device distributes its four analog inputs through an analog crossbar switch on the front end, so it can be configured as either a quad 1.25 Gsample chip, a dual 2.5 Gsample chip, or a single-channel 5 Gsample device, all at 10 bits.

The chip was originally intended, it appears, for use in a famous-brand line of digital oscilloscopes. But it has obvious applications in ATE, multi-band base stations, software-defined radios, and other such areas as well. The part is sampling now, and is built on Jazz Semiconductor's 180 nm SiGe BiCMOS line.

Before we get away from this chip, we should note that there are some interesting details in the design. Each of the four converters on the die uses a folding-interpolating architecture, which division general manager Thierry Gouvernel describes as a somewhat proprietary evolution of the flash converter. (Try here, page 41 if you are really curious.) Folding-interpolating ADCs have been around for a while at low resolutions, but not exactly at this speed. The real secret sauce in the design appears to be the sequencing—to get the four converters interleaved accurately enough that the jitter in the sample-window timing does not intrude on the 10-bit resolution of the converter. There's an interesting clock net in there somewhere, even for BiCMOS.

The company's target customer is designing a sensor-conditioning IC for use at relatively low data rates but high resolution, and with sensors that have either capacitive or resistive outputs. Accordingly, e2v has put together a platform that includes both capacitance- and resistance-bridge input stages, analog signal processing blocks, sigma-delta ADCs with up to 20 bits of effective resolution, and a 32-bit DSP core. The latter is a bit interesting in itself, as it is not an internal design, but rather a version of the Cortus APS core.

To give a sense of what this kind of resolution means, Group general manager Andrew Beaumont said that in one personal locator application, the customer is using a capacitive-bridge sensor to read atmospheric pressure from a pressure sensor. The resolution of the capacitance bridge is 40 aF—yep, attoFarads—giving the device altitude resolution of 10 cm.

The e2v platform approach offers these building blocks in kit form on a development board as a way of breadboarding the design. The development kit includes the usual buttons, little LCD, and interface connectors, along with an FPGA big enough to hold the Cortus core and some user-defined logic. It accepts daughter cards that carry the proprietary e2v sensor interface blocks. So you can plug together a behavioral model of your desired ASIC—probably a real-time, cycle-accurate model, at these speeds—try it in system, and use that as the basis of the back-end design work at e2v. Extending this design approach to mixed-signal environments seems eminently practical.

The e2v mixed-signal ASICs are fabricated at X-Fab, using either a 0.35 or 0.18-micron CMOS process. Beaumont said that selection of X-Fab was the result of a search for an analog-process foundry that not only could understand what e2v's designers needed, but could support the extremely long product lifetimes required in areas such as automotive and medical equipment.