A radio frequency Amplifier is a device that enables an input RF signal to control power from a DC power supply to deliver an RF output signal that bears some relationship to, and is generally greater than, the input signal.
The DC supply voltage available is a primary factor when selecting an amplifier. The most common operating voltages for battery powered systems are 3V (1 Lithium Ion cell), 5V, and 6V (2 cells of Lithium Ion). When an amplifier is operated from a battery, efficiency also becomes a primary concern, to ensure long circuit operation between battery recharges. Common operating voltages for infrastructure ("plugged-in") equipment are 5V, 8V, 12V, and higher. Efficiency is typically less of a concern, however the power supply selected must be able to deliver the necessary current. Less current also equates to longer operating life, and usually smaller circuitry (less heatsinking), so can be important even when large amounts of current are theoretically available. Some GaAs FET-based amplifiers may also requie negative voltages for biasing.
A second important selection criteria for amplifiers is the Bandwidth, or frequency range over which the amplifier has acceptable performance. In most cases the operating frequency of a radio is pre-determined by the application (set by a standard air interface or dictated by a regulatory agency such as the FCC or ETSI). The bandwidth of an amplifier needs to encompass the desired operating frequency range. Excess bandwidth may be discarded through filtering; however in some cases excess bandwidth may lead to reduced efficiency or out-of-band interference.
- Bias Voltage
- Range: <1 V to 20 V
- Operating Frequency Range
- Range: kHz to >50 GHz