Generally, and in one form of the invention, a bias circuit for a transistor amplifier comprising a nonlinear element which limits current flow in a transistor, whereby the output-signal amplitude of the transistor is limited and the transistor is protected from exceeding a maximum current level, is disclosed. In another form of the invention, a bias circuit for a transistor amplifier comprising a nonlinear element 44 which limits current flow through a base terminal of a bipolar transistor 48, whereby the output-signal amplitude of the bipolar transistor 48 is limited and current flow through a collector or an emitter terminal of the transistor 48 is prevented from exceeding a maximum safe level, is disclosed. In still another form of the invention, an amplifier comprising an amplifying transistor 48 and a bias circuit, wherein the bias circuit comprises a nonlinear element 44 which limits current flow through a base terminal of a bipolar transistor 48, whereby the output-signal amplitude of the amplifier is limited and current flow through a collector or an emitter terminal of the amplifying transistor 48 is prevented from exceeding a maximum safe level, is disclosed. In yet another form of the invention, an oscillator circuit comprising an oscillator 92 and an amplifier 94, wherein the amplifier comprises an amplifying transistor and a bias circuit, and wherein the bias circuit comprises a nonlinear element which limits current flow through a base terminal of a bipolar transistor, whereby the output-signal amplitude of the amplifier is substantially constant despite a signal of varying amplitude from the oscillator, is disclosed.
A base bias circuit (1) operates like a constant voltage source, and a base bias voltage generated thereby varies according to fluctuation of the environment temperature without being influenced by the supply voltage, to hold a collector bias voltage constant. The base bias circuit (1) has a function of controlling the base bias voltage according to a control signal coming from the outside. By using a resistor (6) and resistor (14) having suitable resistances, the bipolar transistors constituting the bias circuit (1) can be small in size to reduce the electric current consumed by the bias circuit (1) thereby to make unnecessary the RF choke inductor between a power transistor (13) and the bias circuit (1). In short, the cost is lowered by making the chip size small and by reducing the number of external parts.
The systems and methods described herein provide for composite transistor circuit having a bipolar transistor and a compensation unit. The compensation unit can be configured to stabilize the DC biasing point of the bipolar transistor. The compensation unit can compensate for the self-heating effect in the bipolar transistor and/or improve the linear performance of the bipolar transistor. The compensation unit can include a nonlinear resistor in series with a switch and can be configured to increase the base current into the bipolar transistor as the output voltage of the circuit increases.
Method and apparatus are provided for protecting radio frequency (RF) power amplifiers. A circuit (10) is provided for limiting a supply current to a first stage (Q3) of the RF power amplifier having a second stage (Q2) coupled to the first stage. The circuit comprises a comparator (14) having first and second inputs and an output, and a switching circuit (12, 20, 22, 24) having an input coupled to the output of the comparator (14) and having an output configured to couple to the first stage (Q3). The first input of the comparator (14) is configured to receive the supply current, and the second input is configured to receive a current supplied to the second stage (Q2). The comparator (14) is configured to compare a ratio of the supply current to the first stage to the current supplied to the second stage (Q2) with a predetermined value. The switching circuit (12, 20, 22, 24) is configured to limit the supply current to the first stage (Q3) when the ratio exceeds the predetermined value.
A system (100) and method (200) for adaptively managing bias of an RF power amplifier (102) is provided. The system (100) incorporates a controller (116) configured to select a radio operating mode. A current-mirror circuit (114) is coupled to the controller (116) and configured to produce a reference current (I.sub.Ref) as a function of the radio operating mode. A bias regulator (104) is coupled to the controller (116) and the current-mirror circuit (114) and configured to produce a driver-stage bias current (I.sub.b1) and an output-stage bias current (I.sub.b2) for the power amplifier (102) in response to the reference current (I.sub.Ref). The system (100) also incorporates a DC-to-DC converter (118) coupled to the controller (116) and configured to provide a supply voltage (V.sub.cc) for the power amplifier (102) in response to the radio operating mode. The system (100) also incorporates an envelope detector (120) configured to produce an envelope current (I.sub.Env) in response to an RF input signal (126). The system (100) causes the reference current (I.sub.Ref) to vary as a function of the envelope current (I.sub.Env).
A single bias block for a single or multiple low voltage RF circuits including one or more amplifiers and one or more single or double balanced mixers with compensation for temperature and integrated circuit process parameters. The power supply may be a lower voltage without sacrificing the dynamic range of the amplifier and/or mixer by applying full power supply voltage to the load with the bias applied to the base circuit through an operational amplifier and/or buffer circuit. For the mixer, a lower noise figure may also be realized by moving the gain control impedance from the emitter to the collector circuit. The circuits may be discrete components or part of an integrated circuit. Methods are disclosed for reducing the power supply voltage without affecting the dynamic range of an amplifier, for temperature and process parameter compensation, and for controlling the gain of a mixer without affecting input or output impedance.
