[time-nuts] Re: Seeking feedback on a HW Architecture for a DIY two channel timer/counter and frequency reference

[Lux, Jim]

On 7/16/22 12:44 PM, Carsten Andrich via time-nuts wrote:
> Hi Erik,
>
> very interesting project. I've been using software-defined radios for 
> 5~6 years now to evaluate our various frequency references (mostly 
> GNSSDOs) [1]. However, the resulting measurement setups are quite 
> expensive (>20k€ for 8 synchronous channels with USRPs X310), bulky 
> (2HE, 500 mm depth), heavy (>10 kg), and power hungry (>100 W). I've 
> been sporadically pondering how to design a cheap and compact, yet 
> highly accurate alternative for about a year now. My current, 
> unverified idea for a quad channel time interval counter is to combine 
> 4 TDC7200 with an STM32's 32-bit timer capture (also has 4 channels). 
> The TDC should enable ~50 ps resolution.
>
could you gang up multiple TICCs somehow?


> How do you plan to implement the edge detection (blocks "A/B edge 
> detect")? What resolution are you designing/hoping for? What's the 
> purpose of the CPLD, i.e., what does it do that the MCU can't?
>
> Best regards,
> Carsten
>
> [1] https://arxiv.org/abs/1803.01438
>
> On 16.07.22 16:31, Erik Kaashoek via time-nuts wrote:
>> Some time ago I have shared some info on the timer/counter project 
>> I'm working on.
>> Based on the excellent feedback from this community I've made some 
>> changes to the HW architecture.
>> The goal is a simple and cheap HW, possibly leading to a product that 
>> can be sold for around $100.
>> An architecture level overview can be found here: 
>> http://athome.kaashoek.com/time-nuts/Architecture_2.JPG
>> Not shown is a touch LCD display that runs the user interface.
>> The device will have two inputs (channels A and B) with AC or DC 
>> coupling, user definable trigger levels and up or down trigger edge.
>> One input will have an optional pre-scaler
>> A third input can be used either for a GPS antenna for the internal 
>> 10MHz GPSDO or for input of an external 10MHz reference.
>> A separate output can provide either the internal 10MHz reference or 
>> a frequency derived by integer divide from this internal reference, 
>> such as 1MHz or 1Hz. The phase of the output is locked by the GPSDO 
>> to the GPS PPS
>> Given the form factor, 4 inputs/output is the maximum possible.
>> Does this setup of inputs/output make sense?
>> Are there any suggestions for improving this architecture?
>> Erik.
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