[time-nuts] Microstepper

[Magnus Danielson]

Hi,

That was not exactly what I was aiming for, but you got one aspect
potentially better than I proposed, that the offset generator is running
off the input. That is for sure a variant I did not think about as I
wrote it, but that was in my mind in an earlier variant of thoughts.

Now, the output I&Q DACs then mix with the I&Q of the offset, thus doing
the same as on the input side, but with opposite direction, and then
summed for an output.

The reference to the offset generator may be the input (as you draw it),
a free-running oscillator or a locked oscillator. When locked, the EFC
is from a separate DAC.

I could probably pull this off directly on a Red Pitaya.

Cheers,
Magnus

On 2019-12-25 01:53, Azelio Boriani wrote:
> Something like this? (see image)
>
> On Wed, Dec 25, 2019 at 1:02 AM Magnus Danielson <magnus at rubidium.se> wrote:
>> Hi,
>>
>> I realize that I lack a microstepper. Consider that I have a stable and
>> low-noise 5 or 10 MHz but I want to resynthesize to correct frequency
>> and do phase-steps, and doing so without too much loss of noise.
>>
>> This has traditionally been done using a variation of techniques, but if
>> we would use some of the things that happened lately, pretty OK
>> performance should be possible to achieve without too much hardware.
>>
>> OK, so after a discussion with Bob, here is one sketch for a
>> possibility, just to toss one proposal to crush into pieces and propose
>> improvements or better versions.
>>
>> So, consider using a modern Silabs chip clocked from an oscillator,
>> producing a offset generator with I/Q and then do an I/Q mixdown to a
>> beat frequency, which is digitized by a pair of ADCs. A pair of DACs
>> produces I/Q which is used to mixed to produce the output signal using
>> the signals from the Silab. The ADCs/DACs can be either be fed to some
>> CPU platform or FPGA. With this platform one can choose to servo the
>> reference oscillator, or just modify the beat received. Maybe use a
>> Raspberry Pi as platform. Rotating the vector and steering the rate of
>> rotation should not be extremely hard to do. The input vector can be
>> added internally or used to steer the oscillator. Either way, the in
>> loop noise from the Silabs will be fairly well suppressed since it only
>> acts as a transfer oscillator.
>>
>> So, suggestions, thoughts and improvements?
>>
>> God Jul and Merry Christmas!
>>
>> Cheers,
>> Magnus
>>
>>
>>
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