News Release from: Fujitsu Microelectronics Europe
Edited by the Electronicstalk Editorial Team on 25 March 2002
DACs raise the performance bar to gigasampling
A new generation of DAC technology from Fujitsu not only increases resolution to 14bit but raises conversion rate to a minimum guaranteed 1Gsample/s, again using CMOS technology.
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A new generation of DAC technology from Fujitsu not only increases resolution to 14bit but raises conversion rate to a minimum guaranteed 1Gsample/s, again using CMOS technology. Previously Fujitsu's launch of the MB86061 represented the world's fastest single port 12bit CMOS digital to analogue convertor (DAC). The device provided a minimum guaranteed conversion rate of 400Msample/s, an achievement which has remained unsurpassed until now.
"This new technology is not simply pushing the performance/resolution boundary, as much as smashing through it", enthused Neil Amos, Director of Fujitsu's Mixed Signal Division.
The new DAC technology has been developed using Fujitsu's advanced mixed signal CS80 0.18um process, featuring the company's now renowned triple-well extension.
Using the very latest deep submicron mixed signal technology lends itself to implementing custom mixed-signal ASIC (MS-ASIC) solutions, integrating substantial preprocessing such as interpolation filters, digital mixers or DDS functions.
Initial versions of the DAC use an LVDS interface to drive the converter core directly and allow full test and characterisation.
Tests, using an Agilent Technologies 81250 fitted with high-speed data generation capability, have demonstrated the minimum guaranteed conversion rate of 1Gsample/s, with typical conversion rates approaching 1.5Gsample/s.
The DAC is housed in Fujitsu's new enhanced fine-pitch ball grid array (EFBGA) package.
The EFBGA range has been developed specifically to meet the needs of high performance mixed signal devices.
Benefits include optimised signal routing within the package, easier PCB tracking and excellent thermal properties assisted by a thermal ball array directly under the device.
Using the 120-ball variant, the package measures 12 x 12mm.
Applications for the new DAC technology will no doubt follow where the existing MB86060 and MB86061 DAC ASSPs have achieved acceptance, including cellular infrastructure, test equipment and video related systems.
Of particular interest is cellular infrastructure, which has been waiting for DAC performance capable of supporting the needs of 3G and beyond.
This development will be key to solving major problems encountered with the basestation transmit (Tx) chain.
The increased DAC performance will enable full multicarrier W-CDMA and GSM implementations while supporting true wideband signal generation required for power amplifier (PA) predistortion techniques.
"PA linearisation, using predistortion, is very much the Holy Grail to achieving significant cost reduction in future base station designs, simply due to savings in the PA", highlighted Paul Maddox, Technical Marketing Manager at Fujitsu's Mixed Signal Division.
Fujitsu acknowledges that speed, or more accurately conversion rate, is not everything, but if available significant gains can be made.
Most importantly it enables a shift from generating signals at Fs/4, traditionally adopted as a means of minimising problems due to spurious products.
An ability to adopt a higher conversion rate and increase the effective oversampling ratio (OSR) will yield performance improvements.
Doubling or even quadrupling the conversion rate has previously been inconceivable, but can now enable higher direct-IF architectures, even with IFs at Fs/8, to enable a single IF up-conversion, eg 125MHz IF with sample rates approaching 1Gsample/s.
This announcement represents an important step in the development of DAC technology.
Four-carrier W-CDMA systems can be implemented at significantly higher IFs compared with today's systems with 'double-digit' decibels of margin in ACPR (adjacent channel power ratio).
Beyond this, Fujitsu has designed a number of proprietary features which, when enabled, deliver further improvements to reach performance levels required for full multicarrier GSM.
Customers are currently working towards gaining early market access by adopting this technology through custom MS-ASIC solutions.
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