[time-nuts] Trimble Thunderbolt 1pps

[Javier Herrero]

On 27.01.2014 15:08, Attila Kinali wrote:
>> In practice, the receiver chip only has one power supply.  It would take
>> extra work to make the switching threshold below ground.
> That's not correct. Standard transceiver chips (like the MAX232 family)
> have an integrated charge pump to get a negative power supply.
>
Hello,

The venerable MC1489 does not need a negative supply, and can have a 
threshold below ground, without too much complication. 
http://www.onsemi.com/pub_link/Collateral/MC1489-D.PDF (the receiver 
circuit diagram is shown)

On the other side, the MAX232 has positive thresholds in the receiver 
side http://datasheets.maximintegrated.com/en/ds/MAX220-MAX249.pdf pag. 6

Regards,

Javier