5.1.4 External LNA Support

The sensitivity of the receiver can be increased by using an external low-noise amplifier. The ATA8210/15 offers the output pin 29/RX_ACTIVE, which can be used to bias the external LNA. The pin signalizes the active time of the receive path. The pin can supply 1.5 mA for a 1.9-3.6V application, while delivering a minimum of 0.9 x V_VS as supply voltage for the LNA. For more details, refer to the ATA8210/ATA8215 UHF ASK/FSK Receiver Data Sheet (9344E), section 4, parameter number 15.60.

The achievable sensitivity improvement can be calculated using a cascaded noise figure calculation according to Friis's formula. The Friis’s formula uses the noise factors instead of noise figures and a linear power gain. The noise figure of the ATA8210/15 is 7.5 dB in Low-band and 8.5 dB in High-band.

For example, an external LNA with a 3 dB noise figure and 10 dB gain improves the system noise figure in Low-band from typical 7.5-3.9 dB. Therefore, the sensitivity values of parameters numbers 4.90-5.60 are improved by typically 3.6 dB. For more details, refer to the ATA8210/ATA8215 UHF ASK/FSK Receiver Data Sheet (9344E).