Hello,
We have two designs with the CC1190 for the 915MHz band, both share the same layout but with different antennas.
One design performs to specifications, with output power at 19dBm, the other design has an output power of -4dBm. The differences are in the antenna, but both designs have an H.FL connector for testing.
Attached is the spectral trace of the bad unit, as you can see, the PA generates spurs all the way down to 66MHz.
I suspect that the ground pad is not properly soldered, can such problem cause this phenomena?
Thanks,
Lior2746.badge tag pa output 1ghz span.xls
The design that generates spurs is most likely oscillating. Check your design against the CC1190 ref designs on the web. Not sure which radio you are using so but there are designs for CC1101+CC1190 and CC1120+CC1190.
The design uses the CC1101 Transceiver. The transceiver does not cause measurable oscillations.
We follow the reference design, except one of the notch filters at the PA output.
Thanks.
Marking on the CC1190 Good PCBs: TI 07J PCCY, marking on the CC1190 on the bad PCB: TI 07J P3X5.
I have examined a bad unit in an X-Ray, there were few bubbles visible on the ground pad, all the device's bond wires seemed to be intact.
Could you post a schematic or at least part of one so we can compare the CC1190 BOM with our reference design? Which filter have you removed?
--PS. Thank you for clicking Verify Answer if this answered your question!
Attached are the schematics of the two versions and Gerber screenshot of the top layers of each version.
As you can see, both layers are similar, one has an extended ground plane and a through hole antenna, the other has an SMT antenna.
8204.tb915pics.rar
The schematics you have attached do not correspond to the latest reference design on the web.
Have you measured on more than one board of each type? If it's a soldering problem not all boards should behave equal. Are ground layers equal on the two boards?
The ground layers are almost identical in the two boards. One board has a 18mm shorter ground plane to allow an SMD antenna.
Removing L3 also removed a feedback loop that caused all the spurs. However, output power remained at -2dBm.
Removing The C19/L4 filter and replacing it with a 47pF capacitor gave a 4dB increase in output power, still far from the required 19dBm.
The issue was resolved, apparently the manufacturer decided that 39nH and 3.9nH inductors are the same.