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Usman Hai
Joined: 08 Apr 2004
Posts: 149
Helped: 3
Location: Canada
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 09 Apr 2004 20:12 numeric control oscillator |
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I need help about NCOs for SDRs.
Whats the difference bw NCO and other Digital Oscillators
Usman Hai
Pakistan
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zorro
Joined: 06 Sep 2001
Posts: 380
Helped: 47
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09 Apr 2004 23:19 digital oscillator in fpga |
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An NCO (Numerically Controlled Oscillator) is a digital Oscillator whose frequency can be Controlled (by a Number), analogously as the frequency of a VCO can be controlled by a Voltage.
Regards
Z
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Usman Hai
Joined: 08 Apr 2004
Posts: 149
Helped: 3
Location: Canada
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10 Apr 2004 20:07 why to use numeric control oscillator |
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Is there any material available on net.
is there any book on this topic.
Can i implement it on FPGA.
Usman Hai
Pakistan
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JNekas
Joined: 11 Mar 2002
Posts: 348
Helped: 3
Location: Russia
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10 Apr 2004 20:30 www.ecdl.hut.fi/~jvan/links.html |
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| May be you will try to use DDS.
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Usman Hai
Joined: 08 Apr 2004
Posts: 149
Helped: 3
Location: Canada
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15 Apr 2004 21:18 concepts+numerically controlled oscillator |
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can any one have IEEEpaper links bout NCO.
Its architecture and about its working.
USMAN HAI
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yeewang
Joined: 04 Feb 2002
Posts: 129
Helped: 5
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16 Apr 2004 2:18 sdr-14 nco |
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quite easy, isn't it?
a table for sine/cosine wave
an accumulator for address
a phase input to accumulate
that's all.
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brmadhukar
Joined: 21 Jun 2002
Posts: 844
Helped: 29
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16 Apr 2004 4:22 nco + phase noise |
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Hi,
1) You will find lot of information on this in Xilinx or Altera websites
2) NCOs are used for generation of variable frequency clocks. For eg. If you are tracking a signal, the frequency may change due to doppler and the NCO helps in changing the local carrier.
3) NCOs are conceptually very simple. You accumulate a number based on the desired frequency and the carry generated is the desired signal. Accumulation is done at fudamental frequency from which the signal has to be derived.
Hope this helps,
BRMadhukar
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Usman Hai
Joined: 08 Apr 2004
Posts: 149
Helped: 3
Location: Canada
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21 Apr 2004 21:09 rom compression methods to implement lut in dds |
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Whats the difference bw DDFS and NCO?
Which one shud i take first to study?
Usman Hai
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tlihu
Joined: 02 Jan 2002
Posts: 669
Helped: 5
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22 Apr 2004 2:48 Numeric Control Oscillators |
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| I guess that NCO is part of DDS, right?
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Usman Hai
Joined: 08 Apr 2004
Posts: 149
Helped: 3
Location: Canada
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23 Apr 2004 18:00 Re: Numeric Control Oscillators |
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Which Algorithm shud i adopt for sine wave generation ?
I m currently working on CORDIC.
Is it useful algo for it?
USMAN HAI
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ddt694
Joined: 12 Dec 2002
Posts: 175
Helped: 5
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25 Apr 2004 10:05 Numeric Control Oscillators |
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the cordic algorithm is not necessary now.
four years ago, i use rom compress algorithm to realize sine wave lookup table. now, for the FPGA's ram blocks being getting more and more bits, i only store 1/4 sine wave for a LUT.
for example, you can realize such a nco only cost one ram block by use spartan 3 series fpga:
1) sine and cosine two channel output
2) each of the output is 8 bit width
3) phase address width is 12bit, say, the LUT has 4096 units, each units is 8 bit width.
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Usman Hai
Joined: 08 Apr 2004
Posts: 149
Helped: 3
Location: Canada
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01 May 2004 16:42 Re: Numeric Control Oscillators |
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Any one have personally designed NCO on simulink.
THANKS in advance
USMAN HAI
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Google
AdSense
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01 May 2004 16:42 Ads |
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goodboy_pl
Joined: 12 Mar 2002
Posts: 243
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01 May 2004 21:26 Re: Numeric Control Oscillators |
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As I know DDS, DDFS and NCO are all the same!
for implementation u need an accumulator pluse a look up table but for higher resulation and lower memory requirement some method for compression is used such as linear interpolation or higher order ones or like taylor series etc...
the method of compression is ranked with compression ratio, lspur level generation and processing power (more or less propertional to power consumption!) .
BEST!
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AndaMan
Joined: 12 Apr 2004
Posts: 31
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04 May 2004 8:42 Re: Numeric Control Oscillators |
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NCO is the digital technic to calculate phase of repeitive frequency in fraction of required hertz (it the technic to chage the frequency) and use phase as index to pick amplitude from (sine or any shape) wave table,
fast, but has accuracy/table size tradeoff.
But cordic algo. is the technic to calculate sine (or others transcandency function) which will give the value of sinewave without table (sequential phase, not random). no table, small, slower.
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dainis
Joined: 15 May 2001
Posts: 1451
Helped: 56
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04 May 2004 17:58 Re: Numeric Control Oscillators |
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DDS (DDFS, NCO) LINKS:
/http://www.ecdl.hut.fi/~jvan/links.html
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Memphis
Joined: 13 Apr 2002
Posts: 61
Helped: 1
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13 Jun 2005 17:05 Numeric Control Oscillators |
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| Can anyone tell me that whether the NCO has the same disadvantage of VCO? for example, NCO is also sensitive for phase noise just like VCO??
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ddt694
Joined: 12 Dec 2002
Posts: 175
Helped: 5
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13 Jun 2005 18:49 Numeric Control Oscillators |
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i do not think they are the same.
if the master clock of the NCO has much phase noise, then the output of the NCO also has.
but the control voltage linearity of the nco is much better than vco.
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Renjith
Joined: 03 Jan 2005
Posts: 179
Helped: 9
Location: India
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14 Jun 2005 8:54 Numeric Control Oscillators |
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NCO,DDS,DDFS all are the same concepts.
u can easily generate and NCO using Xilinx tools and test in any FPGA hardware, as they have NCO ip cores.
it's just a matter of entering the parameters depending on ur resolution.
else, if u want to generate it thrg the simulink and port it to FPGA, thatz also easy with the new tool"systemGenerator". where this NCO is availble as an FPGA blockset. just Drag and drop this block and model it.
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ymq8328
Joined: 26 May 2005
Posts: 58
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14 Jun 2005 12:37 Re: Numeric Control Oscillators |
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| where is the best web sit for NCO ? thanks
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suvendu
Joined: 10 Oct 2004
Posts: 442
Helped: 25
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17 Jun 2005 21:58 Re: Numeric Control Oscillators |
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This type of controller is the digital technic to calculate phase of repeitive frequency in fraction of required hertz and use phase as index to pick amplitude from (sine or any shape) wave table,
fast, but has accuracy.
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freeinthewind
Joined: 20 Oct 2004
Posts: 108
Helped: 1
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23 Jun 2005 3:18 Numeric Control Oscillators |
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| there are 2 practical methods : Look-Up table or CORDIC algorithm. Look-Up table is easy to impliment but it needs more memory , CORDIC algorithm save memory resource but has slower speed.
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