Electronic – Routing VCC with jumpers

ground-planejumpervccvhf

I'm trying to route a new VHF RF receiver (LO is 151MHz, RF is 162MHz). There's a pair of LC filters on this board, as well as a Si5351 oscillator and a crystal. From what I've read, an uninterrupted ground plane becomes especially important when designing boards like these, and I'd like to make sure that's what I build here.

The problem is, my 3v3 VCC is on the left side of the board and it's needed by the Si5135 on the far right. I'm not able to move components around to bring these two closer together (I'm constrained by the microcontroller board I'm using and by the placement of the LC filters.)

Is routing power using jumpers — say, 22AWG — a viable solution here? A simple piece of wire would save me from routing the VCC line all the way across the board, cutting the ground plane in half, and it'd save me the cost of a four layer board. What are the up and down sides of using them?

Edited to add this layout: (with corrected uFL connector and unblocked references)

PCB

  • Bottom right: RF section with LC band pass filter and uFL connector
  • Top right: LO section with low pass filter, Si5351 and crystal (far right)
  • Just left of center: NXP SA636
  • Far left: IF section with two MuRata filters
  • Top left: Demodulator section

Ground planes aren't shown, but will be on both sides of the board. Red traces are front side, green are back. The pinout is for Adafruit's "Feather" boards: Feather


Update, Feb. 6th:
I rerouted the board along the lines of AnalogKid's suggestions and added vias as a'la TimWescott. (I had meant to add these but figured it'd just be confusing in the original post.) Here's the updated board:

PCB-updated

I made sure that U1's decoupling capacitor is between the power supply and U1's pin 5 (the power supply line.) Is the trace there a little long? Either way, I think this layout is significantly improved.

I also added guard vias between the LO, RF, IF and demodulator sections. The pitch should be well under what's required for ~151/162MHz. I also added vias to stitch the front and back ground planes near just about anything marked 'ground', and added some on the "far" side of the 3v3 line on the rear.

Always looking for more info, but even if there isn't this was a huge help. Thanks!

Best Answer

Nothing will work as well as a 4-layer board, but if the costs are that critical then it is worth a try. The wire inductance will be larger than a trace on a pcb layer running above a ground plane. Be sure to have plenty of medium and high frequency decoupling as close as possible to the device pins. Also, the loop inductance will be larger, and the wire will radiate more.

I've seen this done with miniature coax, but my guess is that the added wire prep and assembly labor would cost more than the 2-layer / 4-layer incremental cost these days.

UPDATE: Now that you've posted the board, AND IF it is the green traces you want to replace, you can push most of them to the top side. many of your reference designators are blocked, so this will get messy.

  1. Starting at the far right, bring the 3.3V via left to just above C11, and route a red trace to C2x pin 1 where the via was. Place vias above and below C11, green trace below C11, and red trace to the connector pin 2.

  2. Red trace from the via above C11 to the left of C13 pin 2. Via and green trace below the trace from U1 pin 4, to the existing via near C17 pin 1. You now have two very small islands in the bottom side ground plane.

UPDATE #2. Instead of #2 above, run a red trace from pin 1 of the large round thing (electrolytic cap?) right of the connector, to U1 pin 5. Now the ground plane under the trace from pin 4 will be continuous, and there is only one short "jumper" on the bottom layer.