CC1190 PA output impedance.

When I simulated the CC1120 + CC1190 ref design I used 50 ohm terminations on the PA output/ LNA input.

But: For this design I highly recommend using the reference design since it's not only the impedance that has to be optimal but also the filtering etc.

Why do you want to tweak the matching?

We were not able to duplicate the reference design layout exactly, and we don't have ADS Momentum expertise here. We're trying to duplicate matching network, however, using the information available in the CC1190 datasheet and some missing information, PA output impedance in particular.

The PA impedance has never been measured since the impedance seen into the PA is not a valid small signal parameter as such. If you look at the impedance it will change dependent on the phase of the output signal; The impedance will be different when the level at the PA output is Vdd+max swing and Vdd-max swing. How exactly are you planning to use the PA impedance in your calculations? Note that conjugated match for a PA is not a valid approach.

Are you able to keep the same stack-up as in the reference design? Are you able to post how your layout from the PA pin to the antenna looks like at the moment?

I posted the layout in the "CC1120 and CC1190 guidelines for matching" thread. I think you also replied in it. You make valid points about PA matching. However, I'm already aware of all of them. The stack-up is not exactly the same but close. The distance to ground is 0.3mm. I'm currently short on the CC1190 TX gain. I'm missing ~2.5dB of small gain. The RX gain is now what is advertised in the datasheet. Is there a guidline to get the TX working as advertised without changing RX?

I have worked quite a bit with CC1190 and never looked at the small signal gain.

Have you measured the output power and the harmonics? As I mentioned in the previous post I suspect that part of the signal could leak into other parts of the network.

For CC1190 the Rx match is not very critical and the source impedance may be within a fairly large circle in the smith chart without penalty on the gain/ sensitivity. The load impedance has to be fairly close to 6 ohm to get the expected gain.

What is the expected volume on this? If is't interesting I can see if I can take it into ADS and do a quick sim on it (if you don't want to go public with the volume, send me a friend request).

I've measured output power but no the harmonics. I'll do that next. The volume on this part is not high unfortunately. So before I send you the layout info, I'll try a couple more things. I have one last question. What is the purpose of the 47ohm resistor connected to pin15 and 15nH inductor connected to pin16? They are used in the C1120-CC1190EM schematic. They are not used on the CC1190EM alone. These components make a big difference on the large signal gain. Thanks.

They are used to give correct bias to the internal modules. If my memory serves me right the design started off with two 47 ohm resistors but an inductor had to be used to improve the harmonics.

It is possible to experimentally determine the PA large signal output impedance for your bias conditions and PCB layout.  Once that it known, the PA output match could be designed and optimized.  Another option is to work backwards from the TI reference design (using their PCB design) and determine the PA output impedance.  An EM simulator such as Sonnet could be used to accurately model the TI PCB traces.  Then, the output match could be designed and optimized using your modified PCB layout.

Regards,

Eric Hooker

RF Consultant

https://www.linkedin.com/in/erichookerrfconsultant

Dmitriy,

By the way, what is your TX frequency range?

Regards,

Eric