ncicek / rf-vga Goto Github PK

The seven segment display multiplexing is found to create lots of switching noise on the RF output.
The stm32 runs the seven segment on 3.3V rail and causes di/dt when digit FETs are switched on/off. This noise couples upstream into the 5V regulator's output and leaks into the Vbias of the amplifier.

Two things were needed to eliminate this on the first revision:

• Add series resistor to the 4 FET gates to reduce slew rate (47k worked well - reduces gate slew from 200ns -> 200us)
• Add dedicated 5V regulator to power the Hittite chip

Additional improvement ideas:

• Add bulk cap on input supply
• Add more cap to Vbias
• Add stitiching vias in between Vbias rail and segment lines to reduce any chance of inductive coupling.