Re: 50 cent DDS synthesizer

From	john larkin <jl@glen--canyon.com>
Newsgroups	sci.electronics.design, comp.arch.fpga
Subject	Re: 50 cent DDS synthesizer
Date	2025-10-23 07:36 -0700
Organization	A noiseless patient Spider
Message-ID	<jgekfklf9s7khf3kqf07a1jdcuegik14bi@4ax.com> (permalink)
References	<8fjifkteog2a8s8960dk7lak7kh70lrtta@4ax.com> <10dcmfd$1fcrk$1@dont-email.me>

Cross-posted to 2 groups.

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On Thu, 23 Oct 2025 07:45:48 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

>>john larkin <jl@glen--canyon.com>wrote:
>>>
>>We have a little proto board with a RP2040 Rpi cpu and an Efinix T20
>>FPGA. The Pi configures the FPGA at powerup and then talks SPI to it.
>>
>>We often need programmable clocks so I added a few parts to make a DDS
>>frequency synthesizer. We use a PLL inside the FPGA to spin up a 204
>>MHz clock for the 32-bit phase accumulator. The sine lookup is 4K
>>points and the "dac" is six resistors.
>>
>>This lowpass filter is tacky, but it all works. At 50 MHz, the jitter
>>is a few hundred ps p-p, and that looks mostly like amplitude noise to
>>me.
>>
>>https://www.dropbox.com/scl/fo/336qn643xyilkqz5rc9lp/ADC4ThBQa3B-L5auaTDh8fQ?rlkey=q2qrsbdow816id6wgc4eypuas&dl=0
>>
>>The FPGA 1.2v core supply uses about 30 mA total when this is running
>>at 50 MHz out.
>
>Nice, 250 Ohm is a big load, good the FPGA can handle that.

The MSB actually sees 500 ohms.

>
>I was using R2R for video:
> https://www.electronics-tutorials.ws/combination/r-2r-dac.html

One can buy a real r-2r network cheap, but it's easier to use 0603
resistors that we have in stock.

If you program high drive strength, that T20 is pretty fierce...

https://www.dropbox.com/scl/fi/r97plmw3yvls3kgo0liy1/trion_drive_strength.pdf?rlkey=c3evk5zn7amn9ejx2dbtywter&dl=0

Well, that's what the IBIS model says.



John Larkin
Highland Tech Glen Canyon Design Center
Lunatic Fringe Electronics

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Thread

50 cent DDS synthesizer john larkin <jl@glen--canyon.com> - 2025-10-22 14:49 -0700
  Re: 50 cent DDS synthesizer Jan Panteltje <alien@comet.invalid> - 2025-10-23 07:45 +0000
    Re: 50 cent DDS synthesizer john larkin <jl@glen--canyon.com> - 2025-10-23 07:36 -0700
      Re: 50 cent DDS synthesizer Jan Panteltje <alien@comet.invalid> - 2025-10-23 15:16 +0000
      Re: 50 cent DDS synthesizer "Don" <g@crcomp.net> - 2025-10-23 16:54 +0000
        Re: 50 cent DDS synthesizer Jan Panteltje <alien@comet.invalid> - 2025-10-23 17:20 +0000
          Re: 50 cent DDS synthesizer Martin Brown <'''newspam'''@nonad.co.uk> - 2025-10-23 19:33 +0100
          Re: 50 cent DDS synthesizer Chris Jones <lugnut808@spam.yahoo.com> - 2025-10-24 10:12 +1100
            Re: 50 cent DDS synthesizer Jan Panteltje <alien@comet.invalid> - 2025-10-24 06:56 +0000
              Re: 50 cent DDS synthesizer Martin Brown <'''newspam'''@nonad.co.uk> - 2025-10-24 09:53 +0100
              Re: 50 cent DDS synthesizer Lasse Langwadt <llc@fonz.dk> - 2025-10-24 13:40 +0200
                Re: 50 cent DDS synthesizer john larkin <jl@glen--canyon.com> - 2025-10-24 07:09 -0700
                Re: 50 cent DDS synthesizer Jan Panteltje <alien@comet.invalid> - 2025-10-24 17:17 +0000
              Re: 50 cent DDS synthesizer antispam@fricas.org (Waldek Hebisch) - 2025-10-25 22:00 +0000
                Re: 50 cent DDS synthesizer Jan Panteltje <alien@comet.invalid> - 2025-10-26 08:10 +0000
                Re: 50 cent DDS synthesizer john larkin <jl@glen--canyon.com> - 2025-10-26 07:56 -0700
                Re: 50 cent DDS synthesizer Bill Sloman <bill.sloman@ieee.org> - 2025-10-27 03:19 +1100
                Re: 50 cent DDS synthesizer john larkin <jl@glen--canyon.com> - 2025-10-26 10:08 -0700
                Re: 50 cent DDS synthesizer Bill Sloman <bill.sloman@ieee.org> - 2025-10-27 16:02 +1100
                Re: 50 cent DDS synthesizer antispam@fricas.org (Waldek Hebisch) - 2025-10-27 00:10 +0000
                Re: 50 cent DDS synthesizer Jan Panteltje <alien@comet.invalid> - 2025-10-27 09:52 +0000
                Re: 50 cent DDS synthesizer antispam@fricas.org (Waldek Hebisch) - 2025-10-28 16:31 +0000
                Re: 50 cent DDS synthesizer Jan Panteltje <alien@comet.invalid> - 2025-10-28 17:41 +0000
                Re: 50 cent DDS synthesizer john larkin <jl@glen--canyon.com> - 2025-10-27 07:58 -0700
        Re: 50 cent DDS synthesizer john larkin <jl@glen--canyon.com> - 2025-10-23 11:46 -0700
          Re: 50 cent DDS synthesizer john larkin <jl@glen--canyon.com> - 2025-10-23 18:55 -0700
            Re: 50 cent DDS synthesizer Jan Panteltje <alien@comet.invalid> - 2025-10-24 06:57 +0000
              Re: 50 cent DDS synthesizer Jan Panteltje <alien@comet.invalid> - 2025-10-24 07:38 +0000

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