[time-nuts] Using CPLD/FPGA or similar for frequency
kb8tq at n1k.org
Sat Jun 13 08:49:53 EDT 2015
The whole “weird primitives” thing is why I try to count this stuff in registers (flip flops) used rather than what ever neat name the marketing guys came up with this week that sounds better than “glob of stuff”.
> On Jun 12, 2015, at 11:44 PM, lincoln <lincoln at ampmonkeys.com> wrote:
> It also depends on which device primitives you can use. Xilinx spartan series has an SRL16, 16 bit shift register that can be ganged to form dividers / pre scalers. It only takes up one lut or slice, I forget which.
> On Jun 11, 2015, at 4:11 AM, Bob Camp <kb8tq at n1k.org> wrote:
>> Depending on which chip you are using and how big it is, you can get into the 150 to
>> 500 ps range running a carry chain as a TDC.That’s without getting into things like
>> hand routing and temperature / voltage issues.
>> How big a chip you need will be a function of how high you can get the internal PLL
>> to run while packing a bunch of stuff in the chip. If you can hit 400 MHz, each carry
>> chain will need to handle a bit more than 2.5 ns, but probably less than 5 ns. You
>> can do that with a carry chain a few hundred bits long.
>> There is a bit of handwaving already so this is indeed a guess rather than a design.
>> If you run 320 bit chains and 8 inputs, you will need 2.5K registers for the carry chains.
>> You also will need about 200 registers for the support of each chain, so that adds another
>> 1.6K registers. Something in the 5K register range is a possible way to go for 8 inputs.
>>> On Jun 11, 2015, at 2:04 AM, Gregory Maxwell <gmaxwell at gmail.com> wrote:
>>> On Tue, Jun 9, 2015 at 11:40 AM, Alan Ambrose <alan.ambrose at anagram.net> wrote:
>>>> How about a 1pS resolution TIC? :)
>>>> Or a >12 digit frequency counter? :) :)
>>>> It's not a proper time-nut project unless there's a nutty element...
>>> Well, how complex? Front end with a fast ADC and make a DSP DMTD device?
>>> In terms of simpler things that (AFAIK) one can't go out and buy: a
>>> TIC with 4 or 8 inputs would be an interesting piece of time nut
>>> gear.even if it was 'just' 1ns resolution
>>> Surplus lab TICs are easily had but become quite a pile of equipment
>>> when you want to concurrently measure a half dozen oscillators.
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