DDS Features Chart

Document created by Kevin.G Employee on Apr 11, 2013Last modified by Kevin.G Employee on Apr 2, 2015
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Frequently we're asked for help selecting a DDS with frequency sweeping capability, phase hopping, amplitude control etc. but until now the only way to answer that question was to go based on memory or to look at the datasheets for several DDS parts.  This is where I hope the chart below (and attached) can come in handy.  In it I've tried to include just about every piece of information that I thought could be useful in selecting a DDS.  However this has made the chart quite large and if you're not familiar with our breadth of DDS parts this can be quite confusing.   Just below the chart is a list of what all the different columns mean.  Feedback on this chart and anything here is welcome as I'm always looking for ways to improve it and make it better.

 

To view the chart, click on the image below or download the excel file that's attached to this post.

Features Chart 5.5.png

Chart prints on an 11" x 17" piece of paper.

 

 

Chart Column Descriptions

Part #Part Number
SYSCLK (MHz)Maximum System Clock Speed, IE the max speed of the output DAC
INTLVInterleaving:  Our high speed DDS' are capable of their maximum SYSCLK speed because they run 4 or more DDS cores in parallel at a slower speed and slightly offset in time.  The multiple core outputs are multiplexed/recombined before going to the output DAC which runs at SYSCLK.  Interleaving, combined with the system clock sets the maximum update rate for registers inside the part: SYNC_CLK = SYSCLK/INTLV.  For parts without interleaving the maximum update rate is the SYSCLK speed.
PLL XPLL Multiplication:  For convenience, most high speed DDS parts include an on-chip PLL multiplier that can take a crystal or other oscillator and multiply it up to the maximum SYSCLK speed.
SCLK (MHz)Serial Clock:  Not to be confused with SYSCLK, SCLK is the maximum clock speed of the serial interface.
Control WordWhen writing to most DDS parts, the first word (control word) written to the part indicates which register is being accessed and whether you are requesting a read or w write to that register.  This is the bit-size of the control word.  Combined with ‘Max Reg Size’ and/or the FTW, POW, and ASF columns can give a sense of the maximum update rate when using the serial port.
Max Reg Size
Maximum Register Size
PCLK (MHz)Parallel clock:  Some DDS parts have a parallel interface instead of, or in addition to a serial interface.  This is the maximum clock speed that data can be written to the parallel bus.
Par Bus SizeParallel Bus Size, IE how many bits wide the parallel interface is.  Combined with PCLK, ‘Max Reg Size’ and/or the FTW, POW, and ASF columns can give a sense of the maximum update rate when using the parallel port.
FTWFrequency Tuning Word Size (N):  Used in setting the output frequency of a DDS part.  Typical equation is Fout = FTW * SYSCLK /  2^N.
POWPhase Offset Word Size (N):  Used in setting a phase offset to a DDS output.  Typical equation is Phase_Offset = POW * 360 / 2^N.
ASFAmplitude Scale Factor Size (N):  Used in scaling the DDS’ output amplitude.  Typical equations is Amplitude = ASF * IOUTFS / 2^N where IOUTFS is the full scale current output.  For some DDS parts, the output is a voltage instead of current but the equations is still the same.
OOKOn Off Keying:  A feature for quickly turning the DDS output on and off, sometimes with the amplitude increasing/decreasing to zero/full-scale in a linear fashion.
Single-Tone ProfilesA profile is a set of frequency, phase, and/or amplitude registers.  Once programmed, multiple profiles can quickly be switched between via a set of external pins.  The exceptions are the AD9911/AD9958/AD9959 who’s “profiles” only control one parameter at a time.
FIndicates if single-tone profiles can control frequency.
PIndicates if single-tone profiles can control phase offsets.
AIndicates if single-tone profiles can control amplitude.
Ram SizeSome DDS parts have on-chip RAM for controlling frequency, phase, and/or amplitude.  This is the amount of RAM available, IE the maximum number of frequency, phase, or amplitude values that can be programmed to occur in order.
Ram ProfilesThis is the number of different RAM sweeps that can be programmed to a part and switched between via external pins much in the same way single-tone profiles can be switched.
FIndicates if RAM profiles can control frequency.
PIndicates if RAM profiles can control phase offsets.
AIndicates if RAM profiles can control amplitude.
Sweep GeneratorIndicates if the DDS has a 2nd accumulator, aside from the phase accumulator, for controlling frequency tuning words, phase offset words, and amplitude scale factors.  The sweep generator is only capable of sweeping in a linear fashion.  For non-linear sweeping use a part with RAM.
FIndicates if the sweep generator can control frequency.
PIndicates if the sweep generator can control phase offsets.
AIndicates if the sweep generator can control amplitude.
ND HighIndicates if a part has a No Dwell High feature which is used with a DDS’ sweep generator.  Usually when sweeping up, once the programmed upper limit is reached the DDS output will stay there until told to sweep down.  However if No Dwell High is enabled, once it reaches the upper limit it will instead immediately jump down to the programmed lower sweep limit.
ND Low
Indicates if a part has a No Dwell Low feature which is used with DDS’s sweep generator.  No Dwell Low is the opposite of No Dwell High.  Usually when sweeping down, once the programmed lower limit is reached the DDS output will stay there until told to sweep up.  However if No Dwell Low is enabled, once it reaches the upper limit it will instead immediately jump up to the programmed upper sweep limit.
Ramp ControlIndicates if a part has a Ramp Control feature which is used with DDS’s sweep generator or RAM.  Ramp Control is usually an external pin which allows the user to change the direction of the sweep generator (up or down) at whim.
Ramp HoldIndicates if a part has a Ramp Hold feature which is used with DDS’s sweep generator or RAM.  Ramp Hold is usually an external pin which allows the user to halt sweep generator at its current value. 
CompIndicates if the part has an on-chip comparator.  This is usually useful for converting the sinusoidal output of a DDS into a square wave clock signal.
Special Features & Comments
For everything else about a DDS part that’s worth knowing but not common enough to warrant its own feature column.  Some common “features” to look for are:
               DROVER:  Digital Ramp Over which is an interrupt pin indicating when RAM or sweep generator has finished sweeping.
               Programmable Modulus:  A feature in some DDS parts allowing for more precise or exact output frequencies.  It uses two additional registers on top of FTW and has a typical equation of Fout = SYSCLK/2^N * (FTW + A / B)
               Waveform Generator:  Instead of sinusoidal output, this part can also output square waves and triangle waves.
Eval BoardIndicates if this part has an evaluation board available for purchase.
Note that there are a lot of footnotes throughout this chart indicating exceptions or special notes about a feature.  For information on a particular note, look for the matching number in the ‘Special Features & Comments’ section for that part.

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