GUN-TX Fine Tune Issue Resolved

Recently an issue with the Electron Gun Transmitter GUN-TX was found. When the fine delay is adjusted by a large amount the GUN-RC output could be activated and remain in high state until the falling edge of the next trigger pulse.

A simple work-around is to adjust the fine delay only step-by-step in 10 ps increments, however, because of this issue a new firmware was released that fixes this problem.

The solution is to drive the output signal low every time the fine delay value is changed. The only issue with this approach is that if the delay is changed during active time of the trigger pulse the gun receiver pulse may be cut short. So it is suggested to adjust the delay only when triggers are disabled.

To meet timing constraints with the latest release of FPGA tools the delay and pulse width counters had to be limited to 30 bits. This should not be any issue, because with the 500 MHz clock rate 30 bits still provide > 2 s adjustment range for both the pulse width and delay.