Available as an assembled Module and as a DIY project.
This Module is currently available.
Slew Limiter in the Positive voltage range
The Paperface Era Positive Slew is a dual slew limiter that will only slew upward rising voltages, hence the Positive Slew module name. The module can also be used as a triggered up rising saw wave envelope or a ramp wave LFO when patching the lower pulse output to the start jack.
These merchants probably sell this module. Huh?