4.1.3.2 RFIN Matching

The input impedance of the LNA depends on the RF frequency and the used input. The values shown in parameter no. 8.50 in RF Receiving Characteristics are measured on the application board described in Application Board Design 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. 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 found in RF Receiving Characteristics of the electrical characteristics is measured on the application board with RFIN_LB or RFIN_HB power matched to Ant2 of the application board as described in the following table.

To match the ATA8510/15 RF inputs to Ant2 of the application board, the components described in the following table are required. It is important for the ATA8510/15 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.

Table 4-9. RX Matching Element Values without SPDT (Ant2)
Frequency f_RF[MHz]	L₁	L₂	C₁	C₂	Inductor	Q Inductor at f_RF
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

The matching of the RF inputs, including the SPDT RF switch, shows in the following table. The harmonic filter depicted in Figure 4-7 is not used, meaning C₅ and C₇ are not mounted and a 0Ω resistor is mounted instead of L₆; C₁₆ is always 100 pF.

Table 4-10. RX Matching Element Values with SPDT (Ant1)
Frequency f_RF[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 Q_L 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 R_Loss = 2 x π x f x L and the matching loss with 10 x log10(1 + R_P/R_Loss). Care must, therefore, be taken when choosing the component type of these inductors. For 315 MHz, the R_Loss calculates to 2.3 kΩ using the values from Table 4-9, R_P = 870Ω is taken from parameter no. 8.50 in RF Receiving Characteristics, and the resulting loss is 1.4 dB. This means that sensitivity can be increased by choosing a higher grade inductor (such as a wire-wound inductor).