Low-cost ASK and/or FSK transmitter and transceiver ICs are key components in short-range radio systems designed to work in unlicensed industrial, scientific, and medical (ISM) bands between 300MHz and 450MHz. Applications for these short-range devices (SRDs) include remote keyless entry (RKE), tire-pressure monitoring (TPM), remote-control and security systems.

System design often involves a tradeoff between the output power and the current drain of the transmitter. The power amplifier (PA) on Maxim’s low-cost transmitters and transceivers possesses a unique feature that allows the user to control the RF power/current-drain tradeoff while maintaining high efficiency. Managing that tradeoff is key to maximizing battery life for a particular application.

This application note includes a brief overview of power amplifier theory and presents simulation results for insight into the operation of the PA on all Maxim LFRF transmitters and transceivers.