From: jl@glen--canyon.com   
      
   On Mon, 23 Feb 2026 22:29:16 -0500, Phil Hobbs   
    wrote:   
      
   >On 2026-02-23 22:16, john larkin wrote:   
   >> On Tue, 24 Feb 2026 00:46:22 -0000 (UTC), Phil Hobbs   
   >>  wrote:   
   >>   
   >>> john larkin  wrote:   
   >>>> On 23 Feb 2026 22:57:00 GMT, Uwe Bonnes   
   >>>>  wrote:   
   >>>>   
   >>>>> john larkin  wrote:   
   >>>>> ...   
   >>>>>> That's about 12 power supplies!   
   >>>>>>   
   >>>>>> My new gadget, the PPG (Precision Pulse Generator) only needs about 7.   
   >>>>>>   
   >>>>>> Interestingly, the most critical one, for noise and drift, is the 1.2   
   >>>>>> volt FPGA core supply. 100uV changes the prop delay more than I like.   
   >>>>>>   
   >>>>>>   
   >>>>> Consider some stabilization loop. Some FPGA TDC design use similar   
   >>>>> approaches.   
   >>>>   
   >>>> I'm designing basically an economy DDG, digital delay generator. So   
   >>>> I'm not investing engineering hours or parts cost on extreme   
   >>>> performance.   
   >>>>   
   >>>> So I'll just make the 1.2v supply as good as we reasonably can and   
   >>>> sell whatever it does.   
   >>>>   
   >>>> Prop delay in the FPGA is about inverse on core power supply voltage.   
   >>>> If the supply is noisy, I don't think we could compensate for that in   
   >>>> real time.   
   >>>>   
   >>>> We will know the PCB temperature so maybe we'll compensate for that a   
   >>>> little. That would be a quick test and a bit of code.   
   >>>>   
   >>>   
   >>> Using a backwards PLL to regulate the supply would be pretty amusing,   
   >>> though, you have to admit.   
   >>>   
   >>> Cheers   
   >>>   
   >>> Phil Hobbs   
   >>   
   >> Yes. We couldn't compare the FPGA to an external delay line (they   
   >> aren't very good) so we'd need a clever (and affordable) way to   
   >> compare a prop delay to a clock.   
   >>   
   >> Of course, every time you compile an FPGA design it may change the   
   >> routing radically.   
   >>   
   >> Sometimes the optimizer decides that you really don't need to do   
   >> something at all.   
   >>   
   >> But amusing is the enemy of cheap and done. That's a real problem in   
   >> this industry.   
   >>   
   >>   
   >You're no fun anymore. ;)   
   >   
   >Cheers   
   >   
   >Phil Hobbs   
      
   People have different definitions of fun.   
      
   I think it's fun to design electronics that does cool things with a   
   high p/c ratio.   
      
   Performance/complexity   
   Price/cost   
      
      
   John Larkin   
   Highland Tech Glen Canyon Design Center   
   Lunatic Fringe Electronics   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)