audio/videoZONE Products for the week of September 20, 2004
National Semiconductor Says . . .
ADC08D1000: Gigahertz-Speed Dual ADC Offers High Performance
and Low Power
Innovative Architecture of National's New ADC08D1000 Ideal
for Oscilloscopes, Test and Measurement Equipment, Digital Set-Top Boxes
and Communications Systems
National Semiconductor Corporation announced a new dual high-performance CMOS analog-to-digital converter (ADC) that consumes significantly less power than competitive products while providing the gigahertz speeds necessary for reliable measurements of high-frequency signals. These high-speed, low-power devices are designed specifically for applications such as digital oscilloscopes, automated test equipment (ATE), base stations, satellites and communications systems requiring direct I/Q down-conversion. As one of the key building blocks in system signal path designs, ADCs accurately capture real-world analog information and convert it for processing in the digital domain.
The ADC08D1000 digitizes two input signals to 8-bit resolution at sampling rates up to 1 GSPS while consuming just 1.6 watts from a 1.9 volt nominal supply. By using the innovative fully programmable dual-edge sampling feature, the product can achieve 2 GSPS sampling from one channel by interleaving the two on-chip converters. Both coarse and fine timing adjustments are available, allowing the sampling clock for each channel to be calibrated independently in 0.1 pico-second increments. A three-wire serial bus controls these adjustments, as well as on-chip functionality, and independent gain and offset fine-tuning for I and Q channels. The ultra-low power requirements of the ADC08D1000 enable designers to eliminate fans or heat sinks, saving board space and reducing system cost.
"National's rapidly expanding portfolio of data converter solutions
is enabling dramatic improvements in performance throughout the entire analog
signal path," said Suneil Parulekar, executive vice president, Analog
Products Group. "The new ADC08D1000 extends National's range of high-speed
products to offer designers a choice of the industry's lowest-power, highest-accuracy
products on the market. Our best-in-class ADCs enable system makers to differentiate
their products by offering improved image resolution, enhanced reliability,
smaller form-factors and lower power."
analogZONE Says...
"Lowest power, highest accuracy" are always slightly dodgey terms to bandy about with high end silicon like this. When you are asked to pay this amount of money for an IC you will want to be extremely careful that you do your homework and actually measure the numbers in your application, and not those of a "design targets" data sheet.
The single channel ADC081000 was announced before production in February 2004 because it was the subject of an architecture paper at ISSCC. This is also a pre-production announcement (I don't know why in this case) and the numbers claimed are virtually identical to the single-channel part, with the power increasing only to 1.6 W (from 1.45 W for the single channel) -- which is remarkable -- although standby power follows the numbers increasing to 20 mW (from 9 mW). The only other changes from the single channel are that the aperture delay has increased from 930 ps to 1.3 ns and the bandgap temperature coefficient has changed from a -28 ppm/°C to a +28 ppm/°C. There are also three significant specifcations missing in the form of the pipeline delay, the wake-up time and the auto-calibration cycle time.
The market for high-fequency 8-bit parts has arrived, at last. Early vendors such as TriQuint were 5 years in advance of the need and their GaAs was heavy on the power consumption, as is the SiGe process parts coming from vendors such as TelASIC (they haven't reached 1 Gsample/s yet but they're up to 240 Msample/s at 12 bits). Other vendors with advanced bipolar processes, like Maxim with the MAX104 offer great performance (with 46.5 dB SINAD at 1 Gsample/s, while the National products claim a better number at 47 dB) but the power used is over 5 W!
But National does not have the market all to itself. This new dual product has interleaving capabilities to run as a single-channel 2 Gsample/s converter; as does the Atmel AT84AD001, another dual 8-bit 1 Gsample/s ADC, which has been available for about six months, at $64 less per part. The Atmel part manages 6.8 ENOB compared to the 7.5 from National, 5 dB poorer SINAD at 42 dB, 6 dB worse THD, and 4.5 dB worse SFDR but on the other hand it uses less power -- at 1.4 W -- and you will really have to scratch your head to decide if those number improvements are absolutely essential for your application, and your budget. The National part also comes in a smaller LQFP.
The ADC08D1000 data sheet quotes the input resistance of the two channels as a differential 100 ohms, presumably they meant 50 ohms? It offers a full-power bandwidth of 1.7 GHz and a gain flatness within 1 dB to 1 GHz. The full-scale analog differential input range can be set to either 600 mV or 800 mV (a great help with the noise numbers) and the common-mode output voltage is 1.25 V. Crosstalk between the two channels is quoted as -77 dB, more than adequate for an 8-bit part. Clock must be differential while the LDS outputs are demuxed 1:2 so they can be more easily handled. The part will be fabricated in National's 0.18-micron CMOS.
This is an extremely important part for National. We hope the final numbers match the advance data sheet; if they do there are many sockets out there in high-end oscilloscopes, other instrumentation, direct RF downconversion, satellite receivers, WLAN and other communications systems. The race for a dual 2 Gsample/s 8-bit, and then 10-bit, ADC is going to be the next target; in CMOS it looks today like only a two-way race -- but you never know when there is a group out there who are working in stealth.
The ADC08D1000 will sample and be in production in January 2005 in a LQFP-128 and will ne priced at $219 in 1000-piece lots.