To generate frequencies from approximately 0.5 mHz to 12 MHz with a DDS==20
a minimum clock of >24, say 25 MHz, is required. To be able to go down=20=20
to 0.5 mHz, a phase accumulator of at least 36 bits is required. This=20
will give sub mHz resolution over the entire range. Nice for the low=20 frequencies, but not of much use for MHz frequencies (in this=20 application).=20
=20
Is there any objection to using a smaller phase accumulator and a clock=
pre-scaler to generate the lower frequencies?=20
I see Analog Devices has DDS chips up to 48 bits, so 36 bits would not=20=20
be a problem (except for cost maybe).=20
=20
But al of the DDS chips I find from Analog seem only to implement a=20
fixed sine table/function. Do DDS chips exist that allow downloading an=
arbitrary lookup table with 2^10 - 2^16 entries of 10 - 16 bit each?=20
If no such standard chips exist, I expect I need to implement the DDS=20
in an FPGA. Using a smaller accumulator would probably save some space=20
in the FPGA. Or am I just optoimizing prematurely?=20
On Tuesday, August 16, 2022 at 11:37:41 AM UTC-4, Stef wrote:
To generate frequencies from approximately 0.5 mHz to 12 MHz with a DDS
a minimum clock of >24, say 25 MHz, is required. To be able to go down
to 0.5 mHz, a phase accumulator of at least 36 bits is required. This
will give sub mHz resolution over the entire range. Nice for the low
frequencies, but not of much use for MHz frequencies (in this
application).
Is there any objection to using a smaller phase accumulator and a clock
pre-scaler to generate the lower frequencies?
There is a STRONG objection to shortening the phase word. It will cause problems with close in spurs (which can't be filtered) and reduces your resolution. See below.
Instead of a pre-scaler, use a post divider. A pre-scaler on the clock to the DDS requires the analog filter to be adjusted to suit.
I see Analog Devices has DDS chips up to 48 bits, so 36 bits would not
be a problem (except for cost maybe).
But al of the DDS chips I find from Analog seem only to implement a
fixed sine table/function. Do DDS chips exist that allow downloading an
arbitrary lookup table with 2^10 - 2^16 entries of 10 - 16 bit each?
If you are looking to generate a non-sine waveform, it is not needed, or useful.
If no such standard chips exist, I expect I need to implement the DDS
in an FPGA. Using a smaller accumulator would probably save some space
in the FPGA. Or am I just optoimizing prematurely?
Do you work at Highland Technology?
I've posted about an appropriate solution more than once in s.e.d. Here is a fair summary...
A DDS should be designed to generate a top frequency over a 2:1 range. This is easy stuff, with good accuracy and very low jitter if properly designed, use of a LONG phase word and a good filter after the DAC. It is important to NOT shorten the phase word as that introduces spurs close to the frequency being generated, which can not be filtered out. This is because the truncation of the phase word creates discontinuities which show up as close in spurs. Keep the phase word long and round the sine output to suit a 16 bit DAC. This generates harmonics which are much easier to filter.
You don't need to use a single large table for the sine. sin(a+b) = sin(a)cos(b) + cos(a)sin(b), where a is the msbs of the phase word and b is the lsbs. Use appropriately sized tables for sin(a), cos(b) and a single table for the product cos(a)sin(b). This is practical if (a) and (b) are each truncated a bit. Because sin(b) is always small, this term is always small and does not need to be calculated with full resolution on a and b. This product table also does not require the full word width. Three table lookups, one multiply and one add.
A programmable divider then divides the top frequency by 2**N by counting up to a settable value.
The top frequency can clock a final FF buffer register of your favorite technology to provide the actual pulse output with an appropriate jitter.
The settings of these two units can both be changed on a single clock cycle by writing to a buffer register and updating the actual operational registers simultaneously on a cue. The DDS will continue from the present phase, so will produce one top frequency clock pulse that is an intermediate period. The programmable divider will continue from the current count, either triggering right away, or continuing to count from the present value. Either way it will produce one output pulse that is within the range of the two settings, the prior setting and the new setting.
Does this make sense?
Feel free to drop my name with your boss.
To generate frequencies from approximately 0.5 mHz to 12 MHz with a DDS
a minimum clock of >24, say 25 MHz, is required. To be able to go down
to 0.5 mHz, a phase accumulator of at least 36 bits is required. This
will give sub mHz resolution over the entire range. Nice for the low frequencies, but not of much use for MHz frequencies (in this
application).
Is there any objection to using a smaller phase accumulator and a clock pre-scaler to generate the lower frequencies?
I see Analog Devices has DDS chips up to 48 bits, so 36 bits would not
be a problem (except for cost maybe).
But al of the DDS chips I find from Analog seem only to implement a
fixed sine table/function. Do DDS chips exist that allow downloading an arbitrary lookup table with 2^10 - 2^16 entries of 10 - 16 bit each?
If no such standard chips exist, I expect I need to implement the DDS
in an FPGA. Using a smaller accumulator would probably save some space
in the FPGA. Or am I just optoimizing prematurely?
On 2022-08-17 gnuarm.del...@gmail.com wrote in comp.arch.fpga:=20S=20
On Tuesday, August 16, 2022 at 11:37:41 AM UTC-4, Stef wrote:=20
To generate frequencies from approximately 0.5 mHz to 12 MHz with a DD=
=20a minimum clock of >24, say 25 MHz, is required. To be able to go down=
=20to 0.5 mHz, a phase accumulator of at least 36 bits is required. This=
=20will give sub mHz resolution over the entire range. Nice for the low=
k=20frequencies, but not of much use for MHz frequencies (in this=20
application).=20
=20
Is there any objection to using a smaller phase accumulator and a cloc=
problems with close in spurs (which can't be filtered) and reduces your re= solution. See below.=20pre-scaler to generate the lower frequencies?=20=20
There is a STRONG objection to shortening the phase word. It will cause=
to the DDS requires the analog filter to be adjusted to suit.=20=20
Instead of a pre-scaler, use a post divider. A pre-scaler on the clock =
Ah yes, changing the clock would require adjustment of the output=20=20
filter. Not something you would want to do.=20
=20
How would you post-divide the (arbitrary waveform) output? Or do you=20
mean something else with the post-divide?
=20
I see Analog Devices has DDS chips up to 48 bits, so 36 bits would not=
n=20be a problem (except for cost maybe).=20
=20
But al of the DDS chips I find from Analog seem only to implement a=20
fixed sine table/function. Do DDS chips exist that allow downloading a=
=20arbitrary lookup table with 2^10 - 2^16 entries of 10 - 16 bit each?=
r useful.=20
If you are looking to generate a non-sine waveform, it is not needed, o=
Could you explain this? How would I generate an arbitrary waveform=20
without using a table?
=20If no such standard chips exist, I expect I need to implement the DDS=
=20in an FPGA. Using a smaller accumulator would probably save some space=
No, I do not.in the FPGA. Or am I just optoimizing prematurely?=20=20
Do you work at Highland Technology?
is a fair summary...=20I've posted about an appropriate solution more than once in s.e.d. Here=
I don't read there, so missed that. But are you now talking about an=20 appropriate solution for a specific Highland Technology problem, or a=20 general solution?
This is easy stuff, with good accuracy and very low jitter if properly desi= gned, use of a LONG phase word and a good filter after the DAC. It is impor= tant to NOT shorten the phase word as that introduces spurs close to the fr= equency being generated, which can not be filtered out. This is because the=A DDS should be designed to generate a top frequency over a 2:1 range. =
in(a)cos(b) + cos(a)sin(b), where a is the msbs of the phase word and b is = the lsbs. Use appropriately sized tables for sin(a), cos(b) and a single ta= ble for the product cos(a)sin(b). This is practical if (a) and (b) are each==20
You don't need to use a single large table for the sine. sin(a+b) =3D s=
ng up to a settable value.=20=20
A programmable divider then divides the top frequency by 2**N by counti=
technology to provide the actual pulse output with an appropriate jitter.==20
The top frequency can clock a final FF buffer register of your favorite=
ycle by writing to a buffer register and updating the actual operational re= gisters simultaneously on a cue. The DDS will continue from the present pha= se, so will produce one top frequency clock pulse that is an intermediate p= eriod. The programmable divider will continue from the current count, eithe==20
The settings of these two units can both be changed on a single clock c=
=20=20Not really. I don't need just a sin(a+b) signal, I need to implement=20 arbitrary (not realy arbitrary, but various rather complex) waveforms. I=
Does this make sense?
don't see how your solution will do this, unless I totally misunderstood==20
it.
Feel free to drop my name with your boss.I can do that, but I doubt it it will ring a bell, even with your full=20 name. I believe we live on different continents, so I don't think we=20
have ever met.=20
In comp.arch.embedded Stef <m...@this.is.invalid> wrote:=20=20
To generate frequencies from approximately 0.5 mHz to 12 MHz with a DDS=
=20a minimum clock of >24, say 25 MHz, is required. To be able to go down=
=20to 0.5 mHz, a phase accumulator of at least 36 bits is required. This=
=20will give sub mHz resolution over the entire range. Nice for the low=20 frequencies, but not of much use for MHz frequencies (in this=20 application).=20
=20
Is there any objection to using a smaller phase accumulator and a clock=
=20pre-scaler to generate the lower frequencies?Well, your frequency will be less accurate. To see this let me=20
derive formula for DDS. Let t be DAC clock, T be period of desired=20
signal and assume that we have N samples at uniformly distributed=20
points. At n-th tick of DAC clock real time is nt. In the=20
scale of desired signal this corresponds to nt/T. To get=20
position within period we drop integer part of this, that is=20
take frac(nt/T). Then we need to round to closest sample point.=20
Actually instead of rounding we can multiply by N, add 0.5 as=20
bias and take integer part. So, sample index is:=20
=20
[N frac(nt/T) + 0.5]=20
=20
where [ ] denotes integer part. Assuming that N is power of 2,=20
say 2^m and all arthmetic is in fixed point binary frac above=20
is equvalent to dropping high bits, leaving only m bits before=20
binary point. Integer part means dropping bits after bianary=20
points. So formula simplified to=20
=20
[nNt/T + 0.5] =3D [n*a + b]=20
=20
where a =3D Nt/T and b =3D 0.5 is time shift. Note that taking=20
=20
phi_n =3D n*a + b=20
=20
we have phi_{n+1} =3D (n+1)*a + b =3D a + phi_n so single addition=20
is enough to adjust phase. What is effect of using smaller=20
number of bits to represent phase phi_n? Well, b needs only=20
1 bit, so if Nt/T fits into k bits with k bigger than m + 1,=20
then calculation using k bits gives exactly the same result=20
as calculation using infinite precision. In other words,=20
using k bits we get exact result but possibly for wrong=20
frequency.=20
=20
In general acceptable frequency error depends on application.=20
But since good analog components are more expensive than=20
digital ones, simple heuristic says that resuluting of=20
phase accumulator should not degrade accuracy of=20
oscilator. Assuming few ppm quartz oscilator as source=20
of DAC clock, this means that we need about 20 significant=20
bits in parameter a. OTOH, at moderate freqences we do not=20
want to make big jumps, so parameter a should have m or more=20
zero bits at start. With m =3D 10 we arrive at 30 bits. Add=20
some margin for users that want slightly better results and=20
we arrive at 36 bits. In fact, if you want 0.5 mHz without=20
divisor on DAC clock you will have about 35 zero bits=20
at start of paramter a, so 55 bits phase accumultor would=20
be more appropriate. However, in in few hundreds Hertz=20
range and below pre-divisor on DAC clock seem quite=20
appropriate, so 36 bits + pre-divisor should be OK.
I see Analog Devices has DDS chips up to 48 bits, so 36 bits would not=
=20be a problem (except for cost maybe).=20
=20
But al of the DDS chips I find from Analog seem only to implement a=20 fixed sine table/function. Do DDS chips exist that allow downloading an=
=20arbitrary lookup table with 2^10 - 2^16 entries of 10 - 16 bit each?=20
=20
If no such standard chips exist, I expect I need to implement the DDS=
=20in an FPGA. Using a smaller accumulator would probably save some space=
in the FPGA. Or am I just optoimizing prematurely?If you go for 25 MHz DAC clock your DDS should be doable using=20 sufficiently fast processor. My rough guesstimate is that=20
to produce single sample (addjust phase accumulator, extract=20
bits and copy value) you need about 10 machine instructions,=20
so 250 MIPS processor should be fast enough to generate=20
samples. You probably need a DMA channel to transmit them=20
to DAC. I am not aware of processor with fast enough DAC,=20
but I think that there are processors capable of driving=20
external DAC at that speed.=20
=20
OTOH with 12 MHz signal and 25 MHz DAC clock you essentially=20
are limited to sinusoidal signals, to have more variety=20
you need more samples per period, so either lower signal=20
frequency or higher DAC clock. So you may end up with=20
much higher DAC freqency and censequenty be forced to=20
use FPGA.=20
=20
As I wrote earler, skimming bits on phase accumulator seems=20
unwise, it is at most one instruction in critical loop=20
in CPU realization and has _much_ smaller impact on=20
FPGA (think about size of your tables, single counter=20
is tiny compared to that).=20
On Wednesday, August 17, 2022 at 7:36:42 AM UTC-4, Stef wrote:=20DDS=20
On 2022-08-17 gnuarm.del...@gmail.com wrote in comp.arch.fpga:=20
On Tuesday, August 16, 2022 at 11:37:41 AM UTC-4, Stef wrote:=20
To generate frequencies from approximately 0.5 mHz to 12 MHz with a =
wn=20a minimum clock of >24, say 25 MHz, is required. To be able to go do=
s=20to 0.5 mHz, a phase accumulator of at least 36 bits is required. Thi=
=20will give sub mHz resolution over the entire range. Nice for the low=
ock=20frequencies, but not of much use for MHz frequencies (in this=20
application).=20
=20
Is there any objection to using a smaller phase accumulator and a cl=
se problems with close in spurs (which can't be filtered) and reduces your = resolution. See below.=20pre-scaler to generate the lower frequencies?=20=20
There is a STRONG objection to shortening the phase word. It will cau=
k to the DDS requires the analog filter to be adjusted to suit.=20=20
Instead of a pre-scaler, use a post divider. A pre-scaler on the cloc=
ot=20=20Ah yes, changing the clock would require adjustment of the output=20 filter. Not something you would want to do.=20
=20
How would you post-divide the (arbitrary waveform) output? Or do you=20 mean something else with the post-divide?=20
=20
I see Analog Devices has DDS chips up to 48 bits, so 36 bits would n=
=20be a problem (except for cost maybe).=20
=20
But al of the DDS chips I find from Analog seem only to implement a=
an=20fixed sine table/function. Do DDS chips exist that allow downloading=
=20arbitrary lookup table with 2^10 - 2^16 entries of 10 - 16 bit each?=
or useful.=20=20
If you are looking to generate a non-sine waveform, it is not needed,=
he number of phase bits. I described the process below.Could you explain this? How would I generate an arbitrary waveform=20 without using a table?It's not without a table, but not one huge table, 2^n length where n is t=
S=20If no such standard chips exist, I expect I need to implement the DD=
ce=20in an FPGA. Using a smaller accumulator would probably save some spa=
one of his people enquire about such problems here when they potentially in= volve FPGAs. Sorry I mistook you for that.Ok, someone there was inquiring about the exact same thing and often has =No, I do not.in the FPGA. Or am I just optoimizing prematurely?=20=20
Do you work at Highland Technology?=20
re is a fair summary...=20I've posted about an appropriate solution more than once in s.e.d. He=
=20=20I don't read there, so missed that. But are you now talking about an=20 appropriate solution for a specific Highland Technology problem, or a=
r it. But you can do very well with numerical methods and much smaller tabl=general solution?The DDS is general. A single sine table is fine if you have the memory fo=
.. This is easy stuff, with good accuracy and very low jitter if properly de= signed, use of a LONG phase word and a good filter after the DAC. It is imp= ortant to NOT shorten the phase word as that introduces spurs close to the = frequency being generated, which can not be filtered out. This is because t=A DDS should be designed to generate a top frequency over a 2:1 range=
sin(a)cos(b) + cos(a)sin(b), where a is the msbs of the phase word and b i==20
You don't need to use a single large table for the sine. sin(a+b) =3D=
ting up to a settable value.=20=20
A programmable divider then divides the top frequency by 2**N by coun=
te technology to provide the actual pulse output with an appropriate jitter= ..=20=20
The top frequency can clock a final FF buffer register of your favori=
cycle by writing to a buffer register and updating the actual operational = registers simultaneously on a cue. The DDS will continue from the present p= hase, so will produce one top frequency clock pulse that is an intermediate==20
The settings of these two units can both be changed on a single clock=
I=20=20Not really. I don't need just a sin(a+b) signal, I need to implement=20 arbitrary (not realy arbitrary, but various rather complex) waveforms. =
Does this make sense?=20
d=20don't see how your solution will do this, unless I totally misunderstoo=
didn't seem to mention that. It only talked about sine waves.it.Ok, if you need an AWG, then you need a large memory. Your original post =
=20Feel free to drop my name with your boss.=20I can do that, but I doubt it it will ring a bell, even with your full=
name. I believe we live on different continents, so I don't think we=20 have ever met.Sorry, I was mistaken thinking you worked at Highland Tech.=20
In comp.arch.embedded Stef <me@this.is.invalid> wrote:
To generate frequencies from approximately 0.5 mHz to 12 MHz with a DDS
a minimum clock of >24, say 25 MHz, is required. To be able to go down
to 0.5 mHz, a phase accumulator of at least 36 bits is required. This
will give sub mHz resolution over the entire range. Nice for the low
frequencies, but not of much use for MHz frequencies (in this
application).
Is there any objection to using a smaller phase accumulator and a clock
pre-scaler to generate the lower frequencies?
Well, your frequency will be less accurate. To see this let me
derive formula for DDS.
If no such standard chips exist, I expect I need to implement the DDS
in an FPGA. Using a smaller accumulator would probably save some space
in the FPGA. Or am I just optoimizing prematurely?
If you go for 25 MHz DAC clock your DDS should be doable using
sufficiently fast processor. My rough guesstimate is that
to produce single sample (addjust phase accumulator, extract
bits and copy value) you need about 10 machine instructions,
so 250 MIPS processor should be fast enough to generate
samples. You probably need a DMA channel to transmit them
to DAC. I am not aware of processor with fast enough DAC,
but I think that there are processors capable of driving
external DAC at that speed.
OTOH with 12 MHz signal and 25 MHz DAC clock you essentially
are limited to sinusoidal signals, to have more variety
you need more samples per period, so either lower signal
frequency or higher DAC clock. So you may end up with
much higher DAC freqency and censequenty be forced to
use FPGA.
As I wrote earler, skimming bits on phase accumulator seems
unwise, it is at most one instruction in critical loop
in CPU realization and has _much_ smaller impact on
FPGA (think about size of your tables, single counter
is tiny compared to that).
On Wednesday, August 17, 2022 at 7:36:42 AM UTC-4, Stef wrote:
On 2022-08-17 gnuarm.del...@gmail.com wrote in comp.arch.fpga:
On Tuesday, August 16, 2022 at 11:37:41 AM UTC-4, Stef wrote:
But al of the DDS chips I find from Analog seem only to implement a
fixed sine table/function. Do DDS chips exist that allow downloading an >> >> arbitrary lookup table with 2^10 - 2^16 entries of 10 - 16 bit each?
If you are looking to generate a non-sine waveform, it is not needed, or useful.Could you explain this? How would I generate an arbitrary waveform
without using a table?
It's not without a table, but not one huge table, 2^n length where n is the number of phase bits. I described the process below.
No, I do not.If no such standard chips exist, I expect I need to implement the DDS
in an FPGA. Using a smaller accumulator would probably save some space >> >> in the FPGA. Or am I just optoimizing prematurely?
Do you work at Highland Technology?
Ok, someone there was inquiring about the exact same thing and often has one of his people enquire about such problems here when they potentially involve FPGAs. Sorry I mistook you for that.
I've posted about an appropriate solution more than once in s.e.d. Here is a fair summary...I don't read there, so missed that. But are you now talking about an
appropriate solution for a specific Highland Technology problem, or a
general solution?
The DDS is general. A single sine table is fine if you have the memory for it. But you can do very well with numerical methods and much smaller tables as well.
Ok, if you need an AWG, then you need a large memory. Your original post didn't seem to mention that. It only talked about sine waves.
Feel free to drop my name with your boss.I can do that, but I doubt it it will ring a bell, even with your full
name. I believe we live on different continents, so I don't think we
have ever met.
Sorry, I was mistaken thinking you worked at Highland Tech.
On 2022-08-17 anti...@math.uni.wroc.pl wrote in comp.arch.embedded:=20S=20
In comp.arch.embedded Stef <m...@this.is.invalid> wrote:=20
To generate frequencies from approximately 0.5 mHz to 12 MHz with a DD=
=20a minimum clock of >24, say 25 MHz, is required. To be able to go down=
=20to 0.5 mHz, a phase accumulator of at least 36 bits is required. This=
=20will give sub mHz resolution over the entire range. Nice for the low=
k=20frequencies, but not of much use for MHz frequencies (in this=20
application).=20
=20
Is there any objection to using a smaller phase accumulator and a cloc=
=20<snip detailed DDS math>pre-scaler to generate the lower frequencies?=20=20
Well, your frequency will be less accurate. To see this let me=20
derive formula for DDS.
=20
If no such standard chips exist, I expect I need to implement the DDS=
=20in an FPGA. Using a smaller accumulator would probably save some space=
That is assuming the processor has not much else to do and that only a=20 single DDS channel is required. Both will not be true in the possible=20 application, I'm affraid. The additional DDS channels can be a bit=20in the FPGA. Or am I just optoimizing prematurely?=20=20
If you go for 25 MHz DAC clock your DDS should be doable using=20 sufficiently fast processor. My rough guesstimate is that=20
to produce single sample (addjust phase accumulator, extract=20
bits and copy value) you need about 10 machine instructions,=20
so 250 MIPS processor should be fast enough to generate=20
samples. You probably need a DMA channel to transmit them=20
to DAC. I am not aware of processor with fast enough DAC,=20
but I think that there are processors capable of driving=20
external DAC at that speed.
slower, so it may still be doable.
=20OTOH with 12 MHz signal and 25 MHz DAC clock you essentially=20Yes, this is understood. Read the 10 MHz as bandwidth, not as the max=20 frequency at which a complex waveform should be generated. So the=20
are limited to sinusoidal signals, to have more variety=20
you need more samples per period, so either lower signal=20
frequency or higher DAC clock. So you may end up with=20
much higher DAC freqency and censequenty be forced to=20
use FPGA.
waveform will degrade to a sine when sped up to 10 MHz.
As I wrote earler, skimming bits on phase accumulator seems=20FPGA have memory blocks to hold such tables. A simple ripple counter=20
unwise, it is at most one instruction in critical loop=20
in CPU realization and has _much_ smaller impact on=20
FPGA (think about size of your tables, single counter=20
is tiny compared to that).
will indeed take a tiny amount of logic, a synchronous counter will take=
more, certainly at 55 bits. But I think you need an adder if you want=20 variable accumulator steps and not only +1. Keeping the adder small=20
enough to fit in something like a 48-bit DSP slice will probably save=20 space.=20
The above is probably quite Xilinx specific, as that is the last FPGA I==20
have experience with. And even that was a while ago.=20=20
=20
But again, I may be worrying too much about space already. When it comes=
to it, I should first implement the 'best' solution. And then probably=20 find that this uses less than 10% of my FPGA. :-)=20
On 2022-08-18 gnuarm.del...@gmail.com wrote in comp.arch.fpga:=20=20
On Wednesday, August 17, 2022 at 7:36:42 AM UTC-4, Stef wrote:=20<snip>
On 2022-08-17 gnuarm.del...@gmail.com wrote in comp.arch.fpga:=20
On Tuesday, August 16, 2022 at 11:37:41 AM UTC-4, Stef wrote:
But al of the DDS chips I find from Analog seem only to implement a=
g an=20fixed sine table/function. Do DDS chips exist that allow downloadin=
?arbitrary lookup table with 2^10 - 2^16 entries of 10 - 16 bit each=
'Hidden' AWG hint., or useful.=20
If you are looking to generate a non-sine waveform, it is not needed=
the number of phase bits. I described the process below.=20Could you explain this? How would I generate an arbitrary waveform=20=20
without using a table?=20
It's not without a table, but not one huge table, 2^n length where n is=
DS=20=20
=20
If no such standard chips exist, I expect I need to implement the D=
ace=20in an FPGA. Using a smaller accumulator would probably save some sp=
s one of his people enquire about such problems here when they potentially = involve FPGAs. Sorry I mistook you for that.=20No, I do not.=20in the FPGA. Or am I just optoimizing prematurely?=20=20
Do you work at Highland Technology?=20
Ok, someone there was inquiring about the exact same thing and often ha=
I suspected something like this was the case, no problem. :-)ere is a fair summary...=20
=20
I've posted about an appropriate solution more than once in s.e.d. H=
=20=20I don't read there, so missed that. But are you now talking about an=
=20appropriate solution for a specific Highland Technology problem, or a=
for it. But you can do very well with numerical methods and much smaller ta= bles as well.general solution?=20=20
The DDS is general. A single sine table is fine if you have the memory =
Yes DDS is general. But your method seemed to be aimed specifically at a==20
certain problem. But if I understand you correctly, the method you=20 describe is a general solution to generate sine waves without large=20 tables?=20
t didn't seem to mention that. It only talked about sine waves.Ok, if you need an AWG, then you need a large memory. Your original pos=
Re-reading my original post, I see that was a bit hidden in the text and==20
may not have been clear to a reader not familiar with the application.=20 Sorry about that.
You keep calling it a DDS, which apparently is correct in that it can be used generically. But conventionally this refers to generating a sine wave. The term, AWG (Arbitrary Waveform Generator) is more commonly used for what you are doing.
On 2022-08-18 gnuarm.del...@gmail.com wrote in comp.arch.fpga:
You keep calling it a DDS, which apparently is correct in that it can be used generically. But conventionally this refers to generating a sine wave. The term, AWG (Arbitrary Waveform Generator) is more commonly used for what you are doing.To me, the core of the DDS is the clock/phase accumulator/control word.
The phase output of this can be fed to any phase to amplitude conversion
you like. Complete DDS chips often include sine (table), sawtooth
(direct phase to DAC) and pulse (MSB of phase).
Although not an authoritive source, wikipedia agrees with this interpretation.
https://en.wikipedia.org/wiki/Direct_digital_synthesis
AWG, to me, just means you can generate any waveform. But not how you
set the frequency of this waveform. It can be fixed or just use divide
by 2 stages on the clock, or wathever.
But this is all just personal interpretations, I think we both
understand what the other means right now. Maybe we should call it an
DDS AWG generator to cover everything. ;-)
On 2022-08-18 gnuarm.del...@gmail.com wrote in comp.arch.fpga:
You keep calling it a DDS, which apparently is correct in that it can be used generically. But conventionally this refers to generating a sine wave. The term, AWG (Arbitrary Waveform Generator) is more commonly used for what you are doing.To me, the core of the DDS is the clock/phase accumulator/control word.
The phase output of this can be fed to any phase to amplitude conversion
you like. Complete DDS chips often include sine (table), sawtooth
(direct phase to DAC) and pulse (MSB of phase).
Although not an authoritive source, wikipedia agrees with this interpretation.
https://en.wikipedia.org/wiki/Direct_digital_synthesis
AWG, to me, just means you can generate any waveform. But not how you
set the frequency of this waveform. It can be fixed or just use divide
by 2 stages on the clock, or wathever.
But this is all just personal interpretations, I think we both
understand what the other means right now. Maybe we should call it an
DDS AWG generator to cover everything. ;-)
On Friday, August 19, 2022 at 5:13:11 AM UTC-4, Stef wrote:
On 2022-08-18 gnuarm.del...@gmail.com wrote in comp.arch.fpga:
You keep calling it a DDS, which apparently is correct in that it can be used generically. But conventionally this refers to generating a sine wave. The term, AWG (Arbitrary Waveform Generator) is more commonly used for what you are doing.To me, the core of the DDS is the clock/phase accumulator/control word.
The phase output of this can be fed to any phase to amplitude conversion
you like. Complete DDS chips often include sine (table), sawtooth
(direct phase to DAC) and pulse (MSB of phase).
Although not an authoritive source, wikipedia agrees with this
interpretation.
https://en.wikipedia.org/wiki/Direct_digital_synthesis
AWG, to me, just means you can generate any waveform. But not how you
set the frequency of this waveform. It can be fixed or just use divide
by 2 stages on the clock, or wathever.
But this is all just personal interpretations, I think we both
understand what the other means right now. Maybe we should call it an
DDS AWG generator to cover everything. ;-)
Sorry, I didn't mean to make a big deal of the nomenclature. So what are you trying to do that isn't obvious, given a phase accumulator and a lookup table?
The frequency is normally set by the increment on the phase accumulator. But maybe that doesn't work so well for an AWG? What sort of waveforms are you interested in generating?
On 2022-08-19 gnuarm.del...@gmail.com wrote in comp.arch.fpga:
On Friday, August 19, 2022 at 5:13:11 AM UTC-4, Stef wrote:I think it is obvious. Phase accumulator points to LUT, but LUT isn't a
On 2022-08-18 gnuarm.del...@gmail.com wrote in comp.arch.fpga:
You keep calling it a DDS, which apparently is correct in that it can be used generically. But conventionally this refers to generating a sine wave. The term, AWG (Arbitrary Waveform Generator) is more commonly used for what you are doing.To me, the core of the DDS is the clock/phase accumulator/control word.
The phase output of this can be fed to any phase to amplitude conversion >>> you like. Complete DDS chips often include sine (table), sawtooth
(direct phase to DAC) and pulse (MSB of phase).
Although not an authoritive source, wikipedia agrees with this
interpretation.
https://en.wikipedia.org/wiki/Direct_digital_synthesis
AWG, to me, just means you can generate any waveform. But not how you
set the frequency of this waveform. It can be fixed or just use divide
by 2 stages on the clock, or wathever.
But this is all just personal interpretations, I think we both
understand what the other means right now. Maybe we should call it an
DDS AWG generator to cover everything. ;-)
Sorry, I didn't mean to make a big deal of the nomenclature. So what are you trying to do that isn't obvious, given a phase accumulator and a lookup table?
sine table but sommething else.
The frequency is normally set by the increment on the phase accumulator. But maybe that doesn't work so well for an AWG? What sort of waveforms are you interested in generating?This is the DDS part (as I interpret it) and this is what I intend to
do. I see no reason why this would not work for AWG. Except when you get
to higher frequencies, you start losing your waveform, until it degrades
to a sine at FS/2 (providing the output filter is correct).
For now, I need to accomodate 'anything you can draw'. So a full phase
to amplitude LUT is required. Length and width TBD.
On 2022-08-19 gnuarm.del...@gmail.com wrote in comp.arch.fpga:
On Friday, August 19, 2022 at 5:13:11 AM UTC-4, Stef wrote:
On 2022-08-18 gnuarm.del...@gmail.com wrote in comp.arch.fpga:
You keep calling it a DDS, which apparently is correct in that it can be used generically. But conventionally this refers to generating a sine wave. The term, AWG (Arbitrary Waveform Generator) is more commonly used for what you are doing.To me, the core of the DDS is the clock/phase accumulator/control word. >> The phase output of this can be fed to any phase to amplitude conversion >> you like. Complete DDS chips often include sine (table), sawtooth
(direct phase to DAC) and pulse (MSB of phase).
Although not an authoritive source, wikipedia agrees with this
interpretation.
https://en.wikipedia.org/wiki/Direct_digital_synthesis
AWG, to me, just means you can generate any waveform. But not how you
set the frequency of this waveform. It can be fixed or just use divide
by 2 stages on the clock, or wathever.
But this is all just personal interpretations, I think we both
understand what the other means right now. Maybe we should call it an
DDS AWG generator to cover everything. ;-)
Sorry, I didn't mean to make a big deal of the nomenclature. So what are you trying to do that isn't obvious, given a phase accumulator and a lookup table?
I think it is obvious. Phase accumulator points to LUT, but LUT isn't a
sine table but sommething else.
The frequency is normally set by the increment on the phase accumulator. But maybe that doesn't work so well for an AWG? What sort of waveforms are you interested in generating?
This is the DDS part (as I interpret it) and this is what I intend to
do. I see no reason why this would not work for AWG. Except when you get
to higher frequencies, you start losing your waveform, until it degrades
to a sine at FS/2 (providing the output filter is correct).
For now, I need to accomodate 'anything you can draw'. So a full phase
to amplitude LUT is required. Length and width TBD.
On Friday, August 19, 2022 at 6:45:53 AM UTC-4, Stef wrote:
I think it is obvious. Phase accumulator points to LUT, but LUT isn't a
sine table but sommething else.
Yes, it is obvious. That's why I'm asking what you are looking for from this discussion.
I don't know what your requirements are, but you can buy low cost AWG board level products and small box level products.
On 2022-08-20 gnuarm.del...@gmail.com wrote in comp.arch.fpga:=20a=20
On Friday, August 19, 2022 at 6:45:53 AM UTC-4, Stef wrote:...
I think it is obvious. Phase accumulator points to LUT, but LUT isn't =
this discussion.sine table but sommething else.=20=20
Yes, it is obvious. That's why I'm asking what you are looking for from=
In my original post, I had 2 questions=20
=20
1) Are there objections to using a prescaler and a shorter phase=20 accumulator for generating frequencies over a wide range?=20
=20
This has been discussed. Conclusions is that you should keep the=20 accumulator as long as possible for best performance.=20
2) Are the complete DDS chips available that have a downloadable LUT,=20 instead of the standard sine table?=20=20
=20
If such chips are available, I may not have to develop a custom=20 (FPGA/CPU/DSP) solution. This question has not been answered and I have=
found non myself sofar.=20
oard level products and small box level products.I don't know what your requirements are, but you can buy low cost AWG b=
At this time there are only general requirements (AWG, 12MHz BW, ...).=20=20
If the project continues, this will be detailed further.=20
=20
Do you have an example of such a board level product? If it can do what=
will be required, it is certainly an option.=20
On Monday, August 22, 2022 at 4:24:41 AM UTC-4, Stef wrote:
On 2022-08-20 gnuarm.del...@gmail.com wrote in comp.arch.fpga:
On Friday, August 19, 2022 at 6:45:53 AM UTC-4, Stef wrote:...
In my original post, I had 2 questionsI think it is obvious. Phase accumulator points to LUT, but LUT isn't a >> >> sine table but sommething else.
Yes, it is obvious. That's why I'm asking what you are looking for from this discussion.
1) Are there objections to using a prescaler and a shorter phase
accumulator for generating frequencies over a wide range?
This has been discussed. Conclusions is that you should keep the
accumulator as long as possible for best performance.
If any of that is from my comments, I retract them. I was thinking of a typical DDS generating a sine wave.
You only need the clock rate to suit the waveform you are generating, such as Nyquist considerations. Your memory is finite, so you have a fundamental trade off between clock rate and duration of the AWG pattern. I don't know your real requirements, so I can't advise you about how to optimize this. It will depend on your particular problem.
2) Are the complete DDS chips available that have a downloadable LUT,
instead of the standard sine table?
If such chips are available, I may not have to develop a custom
(FPGA/CPU/DSP) solution. This question has not been answered and I have
found non myself sofar.
Yeah, I've never used DDS chips, so I couldn't say. As I've mentioned, there are many AWG products at other levels of integration, modules and boards. eBay abounds with them.
I don't know what your requirements are, but you can buy low cost AWG board level products and small box level products.At this time there are only general requirements (AWG, 12MHz BW, ...).
If the project continues, this will be detailed further.
Do you have an example of such a board level product? If it can do what
will be required, it is certainly an option.
Try punching AWG into eBay or one of the other sites.
On 2022-08-22 gnuarm.del...@gmail.com wrote in comp.arch.fpga:=20't a=20
On Monday, August 22, 2022 at 4:24:41 AM UTC-4, Stef wrote:=20
On 2022-08-20 gnuarm.del...@gmail.com wrote in comp.arch.fpga:=20
On Friday, August 19, 2022 at 6:45:53 AM UTC-4, Stef wrote:=20...=20
I think it is obvious. Phase accumulator points to LUT, but LUT isn=
rom this discussion.=20sine table but sommething else.=20=20
Yes, it is obvious. That's why I'm asking what you are looking for f=
typical DDS generating a sine wave.In my original post, I had 2 questions=20=20
=20
1) Are there objections to using a prescaler and a shorter phase=20
accumulator for generating frequencies over a wide range?=20
=20
This has been discussed. Conclusions is that you should keep the=20
accumulator as long as possible for best performance.=20
If any of that is from my comments, I retract them. I was thinking of a=
Most of those comments (and of Waldek) will also apply to AWG in some=20uch as Nyquist considerations. Your memory is finite, so you have a fundame= ntal trade off between clock rate and duration of the AWG pattern. I don't = know your real requirements, so I can't advise you about how to optimize th= is. It will depend on your particular problem.=20
way, so no need to retract. Also the output filter argument is one=20
against switching sample frequency. Ofcourse I can keep the pre-scaler=20 option in mind, but I don't think it should be the initial approach.=20
Only an optimization when really necessary (speed, size, etc).
You only need the clock rate to suit the waveform you are generating, s=
=20=20
=20
2) Are the complete DDS chips available that have a downloadable LUT,=
e=20instead of the standard sine table?=20
=20
If such chips are available, I may not have to develop a custom=20
(FPGA/CPU/DSP) solution. This question has not been answered and I hav=
there are many AWG products at other levels of integration, modules and boa= rds. eBay abounds with them.=20found non myself sofar.=20=20
Yeah, I've never used DDS chips, so I couldn't say. As I've mentioned, =
G board level products and small box level products.=20=20
=20
I don't know what your requirements are, but you can buy low cost AW=
=20At this time there are only general requirements (AWG, 12MHz BW, ...).=
t=20If the project continues, this will be detailed further.=20
=20
Do you have an example of such a board level product? If it can do wha=
7632-2357-0&ssspo=3DMRtVGD4USYW&sssrc=3D2047675&ssuid=3D&widget_ver=3Dartem= is&media=3DCOPY=20Searching on AWG alone will find you a lot of wire. ;-)=20will be required, it is certainly an option.=20=20
Try punching AWG into eBay or one of the other sites.
With "arbitrary waveform generator", I get a lot of complete bench top=20 generators. And a number of (usually the same) cheap bare board units=20
like this one:=20 https://www.ebay.com/itm/221506533974?mkcid=3D16&mkevt=3D1&mkrid=3D711-12=
=20=20
This one is 8-bit 256 sample 100 kSPS. Not enough on every parameter and=
it seems most of these modules have similar specs.=20
=20
But this is the kind of board level product you meant? I hoped for=20 someting that can be placed on a board. Looks like I need to implement=20 something myself if this project continues.=20
There are products out there that do exactly what you want. I found Bitscope, for example, which seems to have a board level product, but their web site is so goofy I can't find actual specs on it. The control panel example they show only provides standard waveforms, not arbitrary. So I'm not sure it is an AWG.
http://bitscope.com/product/BS05/
You might need to contact them.
How many do you need? Is it worth the effort to roll your own? How are you going to provide a waveform input/definition?
On 2022-08-23 gnuarm.del...@gmail.com wrote in comp.arch.fpga:=20scope, for example, which seems to have a board level product, but their we=
=20
...
There are products out there that do exactly what you want. I found Bit=
you going to provide a waveform input/definition?=20=20Indeed a bit goofy, found no specs either. They say arbitrary but only=20 show standard and distorted standard waveforms. Also no indication how=20
http://bitscope.com/product/BS05/=20
=20
You might need to contact them.
to get truly arbitrary data in.
How many do you need? Is it worth the effort to roll your own? How are =
Number is still unknown (to me), but it is for a commercial product. So==20
just sticking in some fancy boards will not be an option. There will be==20
more generators and signal operations and a lot of other stuff, so it=20=20
will be custom board(s) and controllers etc. anyway. And then you have=20 things like form factor and design and more. The AWG bit may in the end=
be the simplest problem to solve.=20
=20
Getting the data in is another thing completely and that will probably=20 involve PC programs and cloud connections. Not my first choice, but=20 understandable from our customer and end user points of view.=20
Sysop: | Tetrazocine |
---|---|
Location: | Melbourne, VIC, Australia |
Users: | 6 |
Nodes: | 8 (0 / 8) |
Uptime: | 37:55:25 |
Calls: | 45 |
Files: | 21,492 |
Messages: | 63,384 |