Analog Devices is claiming a record for its latest 16bit successive approximation (SAR) ADC.

"It is the fastest 16bit SAR in the world," product line director Leo McHugh told Electronics Weekly. "And even lower throughput parts will have higher power this is 130mW at 10Msample/s."

S/N ratio is 92dB. "That is 8dB, 1.3bits, better than any ADC, regardless of architecture," claimed ADI.

Designed in the UK, the AD7626's top rate of 10Msample/s comes predominantly from speeding up the internal feedback DAC - a block essential in a SAR architecture. "One of the key techniques we use is determining more than one bit per bit trial," said McHugh. "We use three comparators and three complete DACs to get two bits per bit trial."

Even with the area overhead of multiple DACs, the converter fits into 5x5mm thanks to a 0.25µm digital CMOS process and a chip scale package.

"One thing with CMOS, is that the tolerances are probably not what we need them to be," said McHugh, "so one of the areas we have improved on is [production] calibration. We tightened all the distributions and every single part is calibrated."

The crucial internal DACs are capacitive sampling types, initially charging 64 capacitors on each to the input voltage and using successive approximation to determine the top six bits.

Two further stages: four bits then six bits, complete the conversion.

With this heavy impulse capacitive load at the input, the firm recommends its low noise (1nV/ΔΣHz) ADA4899-1 as a buffer/gain block to get the best out of the ADC from signal sources with significant output impedance - including retaining the 1LSB INL (integral non-linearity).

To minimise digitally-generated noise, output data is presented through a self-clocked LVDS (low-voltage differential serial) bus.

The firm is aiming at professional applications, particularly digital medical x-ray machines which use large area sensor arrays. "You need 16 bits and there are a lot of pixels so you have thousands of channels," said McHugh. "With the ADC speed, you can multiplex to hundreds of converters, and the small package means you can put it in a small cabinet."

A slower version, the 7625, will be available for applications up to 6Msample/s.

At the same time as releasing its fast SAR converter, ADI has also introduced a low-noise 24bit ΔΣ converter.

The AD7190, from ADI's Irish design house, delivers 7nV_RMS noise and greater than 16bits of noise-free resolution up to 2.4kHz. "At 4.7Hz you get up to 22.5 noise-free bits across all input voltages from 40mV to 5V," said McHugh.

Again made in digital CMOS, this converter includes a programmable gain block to vary its input sensitivity and "the high impedance input blocks the impedance change as the code intensity changes", said McHugh. "You get ±40mV with a gain of 64, and gain can be set from one to 128."

On-chip features include an oscillator, temperature sensor, bridge power-down switch and reference detect monitor as well as a choice of single-ended, pseudo-differential or fully differential input channels.

Also included are simultaneous 50 and 60Hz rejection, offset and gain calibration, open sensor detection, chopped or non-chopped signal, and four general-purpose output pins.

A 'zero-latency' mode is selectable in order to reduce software overheads if a valid conversion per data output is desired.

Foreseen applications are diverse. "Laboratory scales are among the most precise instruments in the world, and when reading an extremely small signal they need high gain and a virtually noise-free environment to ensure an accurate, flicker-free reading," said product line director Mike Britchfield. "At the other end of the spectrum, industrial manufacturers using high-speed hopper and conveyor scales demand fast, error-free processing of packaged goods."

Packaged in a 7.8x6.4mm TSSOP, this converter is sampling now with production quantities available in November.