[time-nuts] Trimble Thunderbolt 1pps

[Javier Herrero]

On 27.01.2014 19:33, Robert Atkinson wrote:
> All the receiver chips I've looked at, ancient and modern, have only positive thresholds. Most have single supplies and clamp the input at 1 diode drop negative WRT common after an input current limiting resistor, see the MC1489 datasheet.
>
Hello,

Not exactly. If you check the MC1489 datasheet from On Semiconductor, 
the thresholds can be programmed with the response control resistor and 
can in fact be negative. (Figures 6 and 7 in the datasheet). The serial 
input resistor forms part of a resistive divider with the feedback 
resistor and the external resistor - not simply a current limiter to the 
diode.

Regards,

Javier