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Analog Devices Expands Radio Frequency IC Offerings with New Family Of Direct Digital Synthesizers
New DDS family delivers high clock speed with record low power dissipation
| The manufacturer says . . . | ChipCenter's Paul O'Shea says . . . |
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Analog Devices Inc. a global provider of high-performance semiconductors for signal processing applications and the market share leader in data converters, today expanded the companyıs already extensive portfolio of radio frequency (RF) ICs with a new family of direct digital synthesizers (DDS). The new chips deliver a 400 MHz clock speed at one-tenth the power consumption of previous solutions. This now enables designers to use DDS for fast frequency hopping at higher output frequencies in more power-sensitive applications. DDS, which is the technique of digitally creating and manipulating sine waves (or other continuous wave forms) in the digital domain, is the preferred technology for applications requiring superior digital frequency agility, output phase control, and excellent phase noise performance. Typical applications include satellite communications, broadband networking, radar, test and measurement, and instrumentation. The new DDS devices are the first in the industry to clock at 400 MSPS and synthesize frequencies of up to 160 MHz while dissipating less than 200 mW of power. Previous DDS chips of comparable resolution could only synthesize frequencies up to 120 MHz and dissipated 2 watts of power. The lower power dissipation now allows designers to use multiple chips on a single PCB with less concern for thermal issues. Additional features of the family include an integrated 14-bit digital-to-analog converter, on-chip random access memory (RAM), phase offset and amplitude control, and multi-chip synchronization. "Designers of radar systems and shaped FSK (frequency-shift keying) communications applications now have increased flexibility and the ability to enhance accuracy, tuning and phase control by using the automatic linear and non-linear frequency sweeping capabilities of these chips," said Kevin Kattmann, product line director for High-Speed Converters, Analog Devices. "This combination of breakthrough speed and power dissipation will extend the attributes of DDS into many new applications that were previously bound by the limitations of traditional analog synthesis technology."
The new DDS family comprises four new 14-bit devices with various added benefits. The feature sets were selected to allow designers to purchase only the functionality needed for the desired application. The four family members and added functionality are the following:
More About the AD9954 Analog Devices' radio frequency (RF) ICs have the high-performance specsısuch as speed and dynamic rangeıthat enable new, highly desirable architectural changes to radio designs that, in turn, reduce component count, decrease cost, and ease design challenges. Analog Devices has a broad portfolio of RF ICs. Among its extensive offerings are direct digital synthesizers (DDS); phase-locked loop synthesizers (PLLs); detectors and logarithmic operational amplifiers; fixed and variable gain amplifiers (VGAs); TruPwrı RF power detectors; mixers, modulators, and demodulators; and 3-V integrated IF amplifiers. Analog Devices, Inc., Ray Stata Technology Center, 804 Woburn Street, Wilmington, MA 01887. Tel: 800-ANALOGD (800-262-5643) For more information visit: Analog Devices DDS |
The AD995x Direct Digital Synthesizer (DDS) family is similar to a previous release, the AD9858, but this newest release is more of a Swiss Army Knife approach because it is a multi-functional device. They are a natural extension to the company's digital-to-analog converter technology because they integrate the DAC on board with the DDS circuitry. They use their best DAC technology and match it with the DDS to get an optimal product. Analog Devices has a broad portfolio of DDS products including some from below 25 mega samples per second, which are low power, low cost, small packages. They also have products that cover the high speed needs and they keep pushing the clock rates and analog frequencies up with introductions like the AD995x family. That was also the direction of the AD9858 with its one gigahertz clock, but the power dissipation of 2.2 watts (which is good at 1 GHz) limits it to certain applications. This AD995X product family provides a lower power source for clocks and the local oscillator functions in communications applications. Briefly, DDS is a technique for creating a waveform in the digital domain. It's generally a sign wave, but it can also be a waveform of any arbitrary nature. You create the waveform and put it into an algorithm or a lookup table that creates a repetitive waveform. That's the beauty of DDS--you have control over every aspect of the waveform that you're generating. These DDS chips are provided with a D/A converter on-board so it takes the digital information and converts it to an analog signal. DDS is phase continuous and fast frequency hopping and allows you to select the output frequency. The design has a standard fixed clock input reference used by the DDS, and then it's divided down with a digital tuning word of 32 bits. A powerful feature of the DDS allows you to make very precise changes to the output frequency. Using a 32 bit frequency tuning word, you can tune the frequency with 2 to the 32nd-power of frequency increments. So if you have a 400 megahertz reference clock, which this new family offers, you have a frequency resolution in the hundreds of micro Hertz range. Comparatively, an analog synthesizer doesn't have that frequency tuning resolution and the analog will also have overshoot, undershoot, and settling time challenges. Analog synthesizers are also orders of magnitude slower in hopping frequencies. DDS grew out of the military necessity for different kinds of radar able to sweep a frequency. Historically the military used DDS, yet their brand of DDS was an expensive, large, rack-mounted instrument that would dissipate 50 watts. Then from radar applications DDS worked its way into becoming used as a general local oscillator in communications systems. Satellite communications systems, networking type systems used DDS because they were frequently hopping channels looking for available open channels for data transmission, such as the credit card for the gas pump application. Some of those OEMs use DDS because they're transmitting from the gas station to the satellite. Test and measurement equipment is also a big user of DDS because it allows you to set any frequency you want, or generate an arbitrary waveform with certain characteristics. Ham radio enthusiasts have also discovered how to integrate the DDS into their equipment. However, there are tradeoffs especially when compared to PLLs. A DDS doesn't replace the PLL in all situations. PLLs obviously operate faster. When you're looking to generate a high-speed single tone reference, you would use a PLL. They'll output a couple of gigahertz and higher with no problem. The DDS is not there yet since the fastest DDS is only about one gigahertz. And that's before you account for the sampled output from the DAC. The output frequency from the DAC is about 40 percent of the clock frequency. Thus, on this 400 mega sample per second part you can expect output frequencies around 160 MHz, and the part does this on less than 200 milliwatts of power, while operating at full speed. You can increase the frequency if you're willing to sacrifice some dynamic range in the frequency domain. However, for the one reference frequency operating at those high speeds, a DDS offers you 2 to the 32nd different output frequencies, with digital control over the phase, the frequency, and the amplitude. Typically, PLLs don't have amplitude control. There are some instances where you wouldn't use a DDS, for example in a cell phone because it uses too much power. Although, some PLL circuits will use a DDS as the reference clock because the DDS has such precision tuning accuracy. The precision would allow you to gain up the frequency to the gigahertz range and still control the accuracy by tuning the DDS reference. The chip's 200 mW power means that designers will be able to put multiple synthesizer chips on a single board without incurring thermal problems. This part also has new features built in such as the ability to synchronize multiple chips. When you want to use multiple chips in a system, it's difficult to know if they are all aligned in time. Traditionally what companies do is write application notes about how to match the clock line and the digital programming lines. Generally, the only thing you can do is use a synchronous reset to all parts in the system that will start at the same time. Analog Devices decided to include a synchronization feature for the AD995x family. Each of the parts generates an output signal, known as the sync clock, for use by other parts in the system. And each of the parts also has synchronization input. You link the synchronization output of a master to the input of other parts to synchronize all the different parts in the system. That's when all the parts are working from a common reference, which is important in quadrature applications. This part enables you to synchronize two parts by using one as the I channel and then adjusting the quadrature channel until it is as good as you can get it. You can adjust it with a phase resolution up to 2 to the 32nd bit precision. That means the DDS has the same accuracy for both frequency and phase tuning. Another notable feature of the part involves a design change from some previous products - they changed from on-board parallel ports to programming the chip with a serial port. This change offers a reduced pin count that many designers will appreciate. The company also achieved a power savings by reducing the voltage from 3.3 V to 1.8 V. But they realized that not everyone is ready to move to 1.8 V, consequently they allowed for a separate power supply domain on the input/output and the digital signals. As a result you can actually power the digital IOs with a 3.3 volt supply. The part also has a digital multiplier immediately before the DAC input, allowing 14 bit amplitude control over the output signal. This is helpful in situations where the part is going to be idling for a time and you want to reduce the signal power of the output signal, or you want to do a low frequency amplitude modulation. Some other features include the placement of an oscillator circuit in the clock input. That means you don't need a crystal oscillator, which results in a cost savings from a dollar, and up to as much as seven dollars, for a high precision crystal. Finally, this design includes a clock multiplier that will multiply a reference clock from 4 to 20 times. So if you have a 25 MHz crystal oscillator and you want it to be 400 MHz, you can program it to multiply by 16 to get the desired 400 MHz. There are differences among the four offerings to meet a variety of needs. You can get more detailed information from each of the data sheets. All parts are available now in 48-lead EPAD-TQFP packages and are priced per unit in 1,000-piece quantities as follows: AD9951 - $13.75; AD9952 - $15.50; AD9953 - $14.75; AD9954 - $17.25. Data sheets:
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