Dual mode amplifier with bias control

Abstract

A dual mode transmitter with bias control is described wherein an RF signal from a system modulator is fed to a gain control circuit, which can be either a voltage controlled amplifier or attenuator. The ultimate transmitter output power level depends on the attenuation/gain of the gain control circuit. The output signal from the gain control circuit is fed to a driver amplifier which amplifies the signal and feeds it to a power amplifier circuit, which may be comprised of several stages of bipolar transistors or GaAs FETs. The modulated signal to be transmitted is then fed from the power amplifier circuit through a coupler to an antenna terminal. The coupler is connected to an RF detector and is used for RF level monitoring. The Rf level signal from the RF detector is applied to a comparator circuit. An improved combination is provided by incorporating a bias control circuit. A Vpwr signal is applied as one input to the bias control circuit and a mode signal is applied as the other input. When the mode signal is 'on' or present it signifies that the digital transmission mode is to be employed. When the mode signal is ' off' or at zero level, it indicates that the analog transmission mode is to be employed. The bias control circuit provides three bias signal outputs, V.sub.b1 applied to the driver amplifier, and V.sub.b2 and V.sub.b3, applied to the power amplifier. The levels of V.sub.b1, V.sub.b2 and V.sub.b3 are varied for the analog and digital transmission modes.