3.7.1.1 Overview

The single pole double throw (SPDT) is an integrated RF switch with low loss (see parameters no. 8.70 in RF Receiving Characteristics and 12.40 in RF Transmit Characteristics). The SPDT contains an additional switchable damping (see parameter no. 8.80 in RF Receiving Characteristics) for the RXMode to improve the blocking behavior of the ATA8510/15 in the presence of strong interferers. If there is a saturation of the Low-Band or High-Band LNA, the damping can be activated by setting FECR.ANDP = 1. The saturation is indicated by the FESR.LBSAT and FESR.HBSAT status bits.

The following figure shows the application of the integrated (SPDT) RF switch.

Because of 4 kV HBM and 200V MM ESD protection capabilities, a capacitance of 2.5 pF per pin and the series inductance have to be incorporated into the RX and TX matching networks.

In TXMode, a DC connection between pin 7/RF_OUT and pin 6/SPDT_TX is needed to achieve the correct DC operation point of the RF switch. The average voltage of the power amplifier output VS_PA/2 can also be measured on pin 4/SPDT_ANT if the TXMode is activated. This DC connection is performed with inductor L₃. The series capacitor C₁₆ of 100 pF is needed because otherwise a 50Ω load would change the DC operation point of the power amplifier. In this case, the transmit output power would be lowered and the harmonic content increased. Filtering, as shown in the following figure, is required to enhance the harmonic rejection of the ATA8510/15.

Due to the high linearity of the SPDT, it is possible to handle up to +14 dBm in TXMode. The isolation from SPDT_ANT to SPDT_RX in TXMode and from SPDT_ANT to SPDT_TX in RXMode is in the 2 dB range and allows receiver and transmitter matching to be independent.

The following table shows the operating modes of the SPDT. All other modes are unsupported and have undefined behavior and must, therefore, be avoided. The insertion losses of these modes are found in parameters no. 8.70, 8.80 in RF Receiving Characteristics and 12.40 in RF Transmit Characteristics. The RF front-end registers shown in the following table control the SPDT RF switch.