We would like to use TCXO for our Si443x design. There is a useful description in the Application Note AN417 (page 5) about TCXO connections, however it isn't shown how to calculate the value of the DC blocking capacitor (referred to as Ccpl in AN417). Could you please advise on how to do this?
According to page 5 of AN417, one has to keep the Xout voltage between 0.8...1.6Vpp.
You can calculate the voltage divider using the following formula:
Xout = Vtcxo * (Ccpl / (Cint + Ccpl))
Using the example shown in the 'DSB321SCB' TCXO's datasheet, the manufacturer states that the voltage output swing is 0.8Vpp min.
In this case you need a 1:1 voltage div ratio for the TCXO. This can be achieved using a 10nF for Ccpl (aka DC blocking capacitor):
10000pF/ (4pF + 10000pF)= 0,9996 ~ 1
The antenna diversity reference designs for the Si443x and Si446x devices use the DPDT RF switch uPG2164, this switch however is designed to target the 2.4-2.5 GHz and 4.9-6.0 GHz frequency ranges.
Why was this switch chosen?
This is a frequently asked question from our customers.
This switch was recommended by NEC directly.
NEC stated that the device actually can also be used at lower frequency bands (315-959MHz) but when used in this configuration DC blocking capacitors of 100pF should be used instead of their published 4pF capacitors.
In our our tests the performance of this configuration was satisfactory.
Alternative RF switches for uPG2164 are provided in the following KBA:
Does Silicon Labs have a PSPICE model to simulate the PA circuit of Si443x or Si446x radios?
Si443x and Si446x RF transceivers have switching mode PA, and because of that we cannot provide such simulation data. If one is interested about custom matching network design we advise reviewing AN435 and AN436 application notes for Si443x devices or AN627 and AN648 application notes for Si446x devices. These documents contain a comprehensive description of the PA matching for the EZRadioPRO product families.