Electronic Design

8-Bit, 2.2-Gsample/s ADC Offers 6.9 ENOB At 1600 MHz

Sometimes it can lighten your day to find a chip that seems to be intended to be its own worst enemy, even if it really isn't. The data sheet for Maxim Integrated Products' MAX109 8-bit, 2.2-Gsample/s analog-to-digital converter (ADC) lists radar warning receivers and light detection and ranging (LIDAR) speed-detection guns as its first two target applications.

In the automotive market, radar detectors are supposed to warn speeders of a police presence. But LIDAR renders them all but useless, as its laser beams are tightly collimated and its response is so rapid. But that's just a first impression, of course. A "call for pricing" note in the product announcement suggests these ADCs won't find their first homes in consumer gear. Radar warning on military aircraft, however, is a different proposition.

The MAX109's 6.9 effective number of bits (ENOB) performance at a 1600-MHz analog input frequency is based partly on its silicon-germanium (SiGe) fabrication process, but even more on architecture. A quantizer and its encoding logic translate the outputs of an innovative comparator into a parallel 8-bit output code that is passed on to the 1:4 demultiplexer. Four separate ports output true low-voltage differential signaling (LVDS) data at speeds of up to 550 Msamples/s per port.

The input track-and-hold with its 2.8-GHz full-power bandwidth accepts and buffers dc and ac-coupled analog input signals and allows a full-scale 500-mV p-p signal input range. The device data sheet, available online at http://datasheets.maxim-ic.com/en/ds/ MAX109.pdf, goes into more detail about how the track-and-hold was designed to deal with aperture width, delay, and jitter as well as about track-and-hold adjustments.

The sampling point is adjustable within a 32-ps range via the voltage applied to an external pin. The quantizer capture point, the time after which the quantizer latches held data, is adjustable between 25 and 50 ps by means of two other pins that provide coarse and fine control.

The design of the comparator and decoding circuitry also reduces out-of-sequence code errors (thermometer bubbles or sparkle codes), guarantees no missing codes, and provides 1014 clock-cycle metastability performance.

The MAX109 was designed for capturing input frequencies in the second Nyquist zone. At 2.2 Gsamples/s and a 300-MHz input frequency, the ADC achieves a 62-dBc spurious-free dynamic range (SFDR) and a 45-dB signal-to-noise ratio (SNR) that remains flat (within 1.6 dB) for input frequencies up to 2 GHz.

The ADC supports either differential or single-ended inputs with a ±250-mV voltage range. The output data is in standard LVDS format demultiplexed internally by that 1:4 demultiplexer. Control inputs allow the interleaving of additional MAX109 devices to increase the effective system-sampling rate. Packaging is a 256-pin spreader ball-grid array (BGA). Consistent with military applications, the MAX109 is specified over the extended –40°C to 85°C temperature range. An evaluation kit will be available.

Other potential applications beyond electronic warfare include digital RF/IF signal processing, high-speed data-acquisition systems and digital oscilloscopes, high-energy physics instrumentation, and automatic test equipment systems.

Maxim Integrated Products

TAGS: Automotive
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