Path: csiph.com!eternal-september.org!feeder.eternal-september.org!.POSTED!not-for-mail From: "Don" Newsgroups: sci.electronics.design,comp.arch.fpga Subject: Re: 50 cent DDS synthesizer Date: Thu, 23 Oct 2025 16:54:31 -0000 (UTC) Organization: A noiseless patient Spider Lines: 56 Message-ID: <20251023a@crcomp.net> References: <8fjifkteog2a8s8960dk7lak7kh70lrtta@4ax.com> <10dcmfd$1fcrk$1@dont-email.me> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Thu, 23 Oct 2025 16:54:33 +0000 (UTC) Injection-Info: dont-email.me; posting-host="a78fd2dcb1567913e3fb5f0ebd7ee59d"; logging-data="2045657"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/x8cOrPVHeoe5Q4r/YvUMJ" Cancel-Lock: sha1:4PaT5QMpy9tXW+fZlL/FZ33mcsE= Xref: csiph.com sci.electronics.design:737094 comp.arch.fpga:38671 john larkin wrote: > Jan Panteltje wrote: >>>john larkin 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. Also, the ability to adjust assembled resistor values works better for me as a DIYer. Here's mouser's offering for the geniuses in our midst, with the foresight to always choose the correct component: Jan's cited tutorial says: Compared to the R-2R DAC, the binary weighted digital-to-analogue converter has an analogue output voltage which is the weighted sum of the individual inputs. Thus it requires a large range of precision resistors within its ladder network, making its design both expensive and impractical for most DAC's requiring lower levels of resolution. Discussions in this group left me with the impression precision resistor fabrication became trivial thanks to the trimming technology of modern lasers? Is the price of precision resistors still a factor? -- 73, Don, KB7RPU veritas _|_ liberabit | https://www.qsl.net/kb7rpu vos |