Hi,

What is the issue that you see with the TX waveform? Have you managed to receive the packets on the RX side?

Daniel

Hi Dmitry,

Our recommendation for 433MHz operation at +20dBm with Si4463 is the following design:

https://www.silabs.com/documents/public/schematic-files/4463CPCE20C460.zip

Although the nominal frequency of this design is 460MHz, 433MHz is quite close and can be used at that frequency with similar performance. Note that this design uses an RF switch to separate TX and RX paths.

For a Direct-tie solution we have a preliminary design, which is optimized for 434MHz operation, but was never fully validated or characterized. Therefore, we cannot guarantee long term PA reliability as we do for the fully characterized matching network designs which are available on the website. If needed, I can send you that design, but as I mentioned above the recommendation is to follow the 4463CPCE20C460 design.

Daniel

Hi Jack,

The easiest way to add external attenuation outside the chip for RX operation is to create a mismatch between the antenna and the LNA inside the chip. In order to maintain the same TX performance, the recommendation is to adjust the value of LR1 parallel inductor near the RXn and RXp pins:

Daniel

Hi,

If the reference design matching network and PCB layout is followed carefully, in that case very similar RF performance can be expected on a custom design. The max. -10dBm output power suggests that the issue is HW related and probably cannot be solved simply by tuning the matching network. I have created a Salesforce case (00228406) for this issue to review the schematic and PCB layout files.

Please continue the discussion in Salesforce case 00228406.

Daniel

Hi,

I have created Salesforce case #00225771 for this issue. The case will likely need deeper investigation starting with reviewing the HW design. Please continue the discussion in the Salesforce case.

Daniel

Hi Simone,

The DPDT switch should work optimally in the frequency of operation (915MHz in this case), but typically these switches work in a wide range of frequencies. You can find a list of recommended DPDT switch types in the following KBA:

https://www.silabs.com/community/wireless/proprietary/knowledge-base.entry.html/2016/09/16/replacement_for_the-R8kM

Daniel

Hi Simone,

If you want to connect both the TX and RX paths to the antennas, then you need a DPDT switch. If only TX or RX is to be used, an SPDT switch is enough.

Daniel

Hi Simone,

The low-pass filter should be separated into two 3-element low-pass filters: one should be added before the RF switch, the other one after the RF switch. For 915MHz the recommended matching network component values for Si4461 Direct-tie configuration are shown in Table 11 in AN627. Before the RF switch the values from the table should be copied: 22pF-6.8nH-3.9pF-6.8nH-3.9pF. After the RF switch the same 3-element low-pass filter can be used: 3.9pF-6.8nH-3.9pF.

Note that we typically recommend DPDT switch for Antenna Diversity to minimize the loss caused by the matching network. In a combined Direct-tie + RF switch solution the Direct-tie connection causes approximately 2dB RX sensitivity hit, while the RF switch also has some additional insertion loss. Overall with a Direct-tie + RF switch combined matching you can expect 3dB RX sensitivity loss compared to a split TX / RX case. With a DPDT switch the TX and RX paths would be separated and thus the only sensitivity loss would be caused the insertion loss of the RF switch which is typically 0.5dB.

Daniel

Hi Simone,

Yes, you can connect the TX and RX paths directly: this is called a Direct-tie matching network. In this case an SPDT switch can be used for Antenna Diversity.

You can find Direct-tie matching network topologies and recommended component values for Si4461 in AN627 (Figure 4, Table 9, Table 11):

https://www.silabs.com/documents/public/application-notes/AN627.pdf

Note that even in this case a 3-element low-pass filter similarly as in the 4463CPCE20A915 design should be added after both antenna ports of the RF switch to suppress possible harmonic re-generation by the RF switch.

Daniel

Hi Simone,

If you want to connect both the TX and RX paths to the antennas, then you need a DPDT switch. If only TX or RX is to be used, an SPDT switch is enough.

Daniel