Matching network design for SE TX (PA output) and DE RX (LNA input)

Hi,
My plan is to design a transceiver similar to one is given in AX5043 Data Sheet Fig. 15 (pp.38). The transmit and receive center frequencies will be slightly (i.e. 10MHz approx.) different. Could you please lead me to a resource giving ANTP-ANTN (differential) and ANTP1 (single ended) complex impedances for different (within the limits of the IC) operating frequencies?
Regards.

Hi @rmozel.
As your RX and TX are at only 10MHz difference I would not bother too much re-adapting the matching network a priori. This because the variability of your PCB manufacturer, and discretes will already detune your network by an extend larger than 10 MHz.

You can use the BOM we recommend in our datasheet, and then eventually, once you will have your prototypes, you could slightly modify some L/C to optimize the efficiency.

Please also find more details on this topic via the forum post: Impedance matching for AX5243 - #3 by georgi.gorine

Best regards,
Georgi

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Hi Georgi,

Thank you for your answer. I’ll also keep your suggestion about the frequency difference.

I’ve checked the link you provide. If I give you more detail you will probably appreciate where I get stuck. I need to design two independent transceiver units, one for 980MHz Rx/Tx and one for 450MHz Rx and 440MHz Tx. The transmitter part of both designs will utilize SE (ANTP1) antenna output of the IC. Thus, I need:

  1. 980MHz SE TX port impedance since I need to match this output to my PA module input.
  2. 980MHz DE LNA port impedance since I need to match this input to my receiver front-end output.
  3. 440MHz SE TX port impedance since I need to match this output to my PA module input. Note: This is quite close to 433MHz I may use and tweak values given in Table 30 of the data sheet.
  4. 450MHz DE LNA port impedance since I need to match this input to my receiver front-end output.

A table similar to that of SiLabs AN643 Table 1. would be very useful for this purpose.

Best Regards,
Renan

Hi @rmozel. We don`t have a table as in the app note you mention.
For the receiver side we have measurements taken at the ANTP and ANTN with different choke inductors (LC1/2)as it is assumed that the same network is used for both TX and RX.

  • Lchoke = 18 nH
    • 25-28j Ohm (868 MHz)
    • 49+86j Ohm (433 MHz)
    • 3.3+23j Ohm (169 MHz)
  • Lchoke = 68 nH
    • 16-22j Ohm (868 MHz)
    • 105+97j Ohm (433 MHz)
    • 26+73j Ohm (169 MHz)
  • Lchoke = 120 nH
    • 15-21j Ohm (868 MHz)
    • 54-85j Ohm (433 MHz)
    • 133+130j Ohm (169 MHz)

For the transmitter side, the impedance changes depending on the power level and transmit frequency. For this reason, the fastest would be for you to copy the BOM from our proposed schematics (where the matching is done to come out at 50 Ohm), and then fine tune it following the same rules explained here FAQ: How to operate AX5043 at 27 MHz - (custom matching networks for AX5043).

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Thank you. That will help anyway.