A biasing network for an RF transistor amplifier is provided wherein the bias varies smoothly and continuously from a value below turn on giving class B operation at low power inputs, to a lower valve giving class C operation at higher power levels, and finally, to a point where the DC dynamic impedance between the base and the emitter of the amplifier is extremely low, promoting maximum transistor gain and efficiency. Linear amplification at RF frequencies over the full range of power inputs is achieved.
An amplifying circuit capable of providing the gain and linearity of Class A amplifier and power conversion efficiency of a Class B or C amplifier is provided. The circuit includes an amplifying device, such as a power transistor, and a biasing network that permits the device to operate in Classes A, B or C depending upon the amplitude of the input signal.
A power detector for detecting the magnitude of a radio frequency (RF) signal comprises a detector transistor (V1) which provides an output signal (DC-OUT) in dependence upon the input RF signal. The detector transistor is biased with a biasing circuit which comprises two transistors (V2,V3) in a feedback loop coupled to the base of the detector transistor (V1). The detector can be used as both current and voltage amplifier. One of the transistors (V3) in the feedback loop provides temperature compensation.
A power amplifier (50) includes two transistors (11, 21) and a dynamic biasing circuit (52). The dynamic biasing circuit (52) uses a sampling circuit (54) to generate a bias adjusting signal proportional to the amplitude of an AC signal at a drain electrode of the first transistor (11). The bias adjusting signal is combined with a constant voltage bias signal to generate a dynamic biasing signal applied to a gate electrode of the second transistor (21). As the gain of the first transistor (11) decreases, the amplitude of the AC signal at its drain electrode decreases. Thus, the dynamic biasing circuit (52) generates a lower dynamic biasing signal at the gate electrode of the second transistor (21), thereby decreasing a quiescent drain current in the second transistor (21) and improving the efficiency of the amplifier (50) at low output power levels.
A microwave power amplifier having application in multiple beam phased antenna array systems including a biasing means connection to the base of a microwave transistor being responsive to radio frequency signals applied to the amplifier to automatically adjust the transistor bias level to maintain constant amplifier gain. The biasing means includes two voltage regulators with their outputs capacitively coupled via a fixed resistor having a value determined by the characteristics of the transistor, the base of the transistor being connected to the biasing means at the junction of the resistor and the capacitive coupling of one of the regulators. The mode of operation of the power amplifier gives rise to a highly efficient linear system while under effective Class B (non-linear) bias.
A linear high power transistor amplifier operable over a wide band of modulation frequencies wherein linearity of response is maintained by use of an active bias circuit.
