4.1.3.1 Overview

In the ATA8510/15, the RF input and output can be connected directly to the antenna by an integrated RX/TX switch, for example, as depicted in Figure 4-8.

The following figure shows the equivalent circuit of the SPDT RF switch in RXMode extracted from 300 MHz to 500 MHz S-parameter measurements without damping activated. The following table summarizes the corresponding equivalent circuit elements. To achieve a 50Ω impedance in RXMode at Ant1 (application board), a standard simulation tool can be used to calculate the element values of the matching network C₄(C₃) and L₁(L₂) shown in Figure 4-21. The equivalent circuit of the SPDT, the input impedance of RFIN_LB(HB) (see parameter no 8.50 in RF Receiving Characteristics) and the parasitics of the individual application board can be used for this calculation. After assembly of the calculated elements on the board, the values for C₄(C₃) and L₁(L₂) must be changed slightly to obtain a nominal reflection magnitude of equal to or less than -20 dB at Ant1.

The following figure shows the equivalent circuit elements of the SPDT RF switch in TXMode extracted from 300 MHz to 500 MHz S-parameter measurements. The following table shows the equivalent circuit element values. For power amplifier matching without SPDT, a capacitor C₅ to GND is at the position of the SPDT, as shown in Figure 4-7. This capacitor is mainly reduced and the inductor kept constant if the SPDT is used. The TX output circuit determines the output power, the harmonic suppression and the TX current. Variation in the external RF components can be used to improve one of these parameters at the cost of the other two.

The following figures indicate the simplified matching circuits from the application board, as shown in Application Board Design with and without using the SPDT, respectively. Except for the harmonic filter, components that are not mounted or those replaced by 0Ω bridge components are not listed to facilitate comprehensibility.