5.1.3.2 RFIN Matching
The input impedance of the LNA depends on the RF and the used input. The values are measured on the application board by connecting the measurement ground to the ground of L1 for Low-band or L2 for High-band and measuring the impedance at the other connection of L1 or L2. See Application Board Design from Related Links. For more details, refer to the ATA8210/ATA8215 UHF ASK/FSK Receiver Data Sheet (9344E), section 4, parameter number 8.50. The capacitance of the application board is calibrated by measuring the unpopulated board and removing the capacitance value from the measurement above.
Most RF performance data is measured on the application board with RFIN_LB or RFIN_HB power matched to Ant2 of the application board (see the following table). For more details, refer to the ATA8210/ATA8215 UHF ASK/FSK Receiver Data Sheet (9344E).
To match the ATA8210/15 RF inputs to Ant2 of the application board, the components described in the following table are required. It is important for the ATA8210/15 that a DC path from pin 1 and pin 2 to ground exists. If the matching circuit is changed, an inductor must always be placed from RFIN_LB or RFIN_HB to ground.
Frequency fRF [MHz] | L1 | L2 | C1 | C2 | Inductor | Q Inductor at fRF |
|---|---|---|---|---|---|---|
315 | 39 nH | Not mounted | 3.3 pF | Not mounted | TOKO LL1608FS39N | 30 |
433.92 | 22 nH | Not mounted | 2.7 pF | Not mounted | TOKO LL1608FS22N | 35 |
868.3 | Not mounted | 8.2 nH | Not mounted | 1.8 pF | TOKO LL1608FS8N2 | 52 |
915 | Not mounted | 8.2 nH | Not mounted | 1.5 pF | TOKO LL1608FS8N2 | 52 |
For the matching of the RF inputs, including the SPDT RF switch, see the following table. The harmonic filter depicted is not used, which means the C5 and C7 are not mounted, and a 0Ω resistor is mounted instead of L6; C16 is always 100 pF. See Input Matching with SPDT on Application Board in the Overview from Related Links.
Frequency fRF [MHz] | L1 | L2 | C4 | C3 | Inductor | Q Inductor |
|---|---|---|---|---|---|---|
315 | 39 nH | Not mounted | 3.6 pF | Not mounted | TOKO LL1608FS39N | 30 |
433.92 | 18 nH | Not mounted | 3.9 pF | Not mounted | TOKO LL1608FS18N | 25 |
868.3 | Not mounted | 8.2 nH | Not mounted | 2.2 pF | TOKO LL1608FS8N2 | 52 |
915 | Not mounted | 6.8 nH | Not mounted | 2.2 pF | TOKO LL1608FS6N8 | 50 |
The quality factor QL of the matching inductors causes losses, which result in diminished sensitivity. These losses can be estimated when calculating the parallel equivalent resistance of the inductor with RLoss = 2 x π x f x L and the matching loss with 10 x log10(1 + RP/RLoss). Care must, therefore, be taken when choosing the component type of these inductors. For 315 MHz, the RLoss calculates to 2.3 kΩ using the values from RX Matching Element Values without SPDT (Ant2), RP = 870Ω, and the resulting loss is 1.4 dB. See RX Matching Element Values without SPDT (Ant2) in the RFIN Matching from Related Links. For more details, refer to the ATA8210/ATA8215 UHF ASK/FSK Receiver Data Sheet (9344E), section 4.0 and parameter number 8.50. This means that sensitivity can be increased by choosing a higher grade inductor (such as a wire-wound inductor).