257	2006-12-23 15:51:53	Ted Bruce KX4OM	MMIC PC Board mounting
Message	Date	From	Subject
Picking up on the thread from W4ZCB's MMIC application, I'm currently building a transmitter driver-amplifier stage for HF based on Fig 11.14 in EMRFD. I've decided to separate the PA and driver stages, particularly the MMICs and the PA due to layout considerations. The PA built by WA3EBY that was published in QST emphasized the critical nature of layout for his use of the MOSFET push-pull PA. My other concern is the MMICs. I have that stage designed for double-sided .032" glass-epoxy PCB material, with a considerable isolation zone around the MMICs. I've tried to duplicate the ground pads for the MMICs in my CAD program (this design is going to be used in at least two transceivers). In The application notes regarding test fixtures for MARs and MAVs from Mini-Circuits, they show the top side of the board with only foil traces, and many holes drilled through the extended ground pads for the MMICs to the other side of the board, presumably ground plane. Other MMIC board photos I've collected show some with top-side foil traces only, and some show both sides ground plane. My current design is for the latter, as I mentioned, with many holes drilled through the ground plane, using "Z" wires to connect them, and of course many more holes around the ground pads for the MMICs. When I initially CADded the entire transmit RF stage, I had a lot of spaghetti traces leading into the PA transistor mounting locations, and from looking at the board photos in EMRFD, and taking to heart the experience of other builders as well, I've decided to separate and simplify driver and PA physical layouts. For a fairly straightforward schematic, this stage of the rig has been the most difficult...I was up to Rev. H before I decided to make the split! I would appreciate any comments regarding the layout considerations, and the use of double and single-sided board. 73, Ted KX4OM
259	2006-12-24 05:11:09	Harold E. Johnson	MMIC PC Board mounting
GM Ted, and Merry Christmas to you and the group. Your comments (about my comments hi) and MMIC's and board construction. Agilent has a beautiful little piece of free software called AppCad where you can do all sorts of manipulation of electronic design. They call the practice of a single land over a ground plane "microstrip" and the use of a groundplane on both sides of a land as well as complete coverage of the opposite side with another ground plane "coplanar waveguide". My experience doesn't extend to the microstrip approach, but I've had nothing but success with the coplaanar approach when done properly. I can't imagine that you'll find any problem with the layout you're proposing, I have several utility amplifiers in the shop using cascaded 0685's and even a couple of 60 dB gain amps using 02186's that are completely tame as a pussycat. LOTS of decoupling, and lots of vias and you're practically guaranteed success. Regards W4ZCB
265	2006-12-24 15:44:48	Ted Bruce KX4OM	MMIC PC Board mounting
Thanks for the input, Harold. It occurred to me after I made the comments that the Mini-Circuits test boards are most likely for well above the HF range, where striplines are used. The ground pads I made for the MMICs are pretty substantial, to be able to drill many holes around them through to the bottom ground plane. As I said, they're well-isolated from the rest of the top foil ground plane. The planes will be well-knitted together, and while there will be distributed capacitance as Rick mentioned with respect to your vias, I'm obviously going to be well below the range where I'd be considering the coplanar sandwich a waveguide. Assuming I don't have oscillati