The DC power applied to a transistor allowing it to operate as an active amplifying or signal generating device. Typical voltage levels in GaAs FETs used in receivers are 1 to 7 volts between the drain and source terminals, and 0 to −5 volts on, or between, the gate and source terminals. For microwave systems, DC voltages and currents, provided by batteries or AC/DC converters required to “bias” transistors to a region of operation where they will either amplify, mix or frequency translate, or generate (oscillators) microwave energy. Since energy can be neither created nor destroyed, microwave energy amplification or creation is accomplished at the expense of DC energy.
Input bias current and input offset current also affect the net offset voltage seen for a given amplifier. The voltage offset due to these currents, however, are separate from the input offset voltage parameter and is related to the impedance of the signal source and of the feedback and input impedance networks such as the two resistors used in the basic inverting and non-inverting amplifier configurations.
There are two main types of biasing: fixed biasing and cathode biasing. Fixed biasing does not mean the bias is not adjustable, in fact, it usually means the opposite. Cathode biasing is usually fixed, and not adjustable, and fixed biasing is usually adjustable with a small trimmer potentiometer, or "trimpot".
The input offset voltage () is a parameter defining the differential DC voltage required between the inputs of an amplifier, especially an operational amplifier (op-amp), to make the output zero (for voltage amplifiers, 0 volts with respect to ground or between differential outputs, depending on the output type).
"Forward bias voltage When the voltage is applied this way round it tends to push the electrons and holes towards the junction. It also reduces the height of the energy barrier and reduces the width of the depletion zone. "
"Reverse bias voltage When the voltage is applied this way round it tends to pull the free electrons and holes apart, and increases the height of the energy barrier between the two sides of the diode."