A transistor is connected to form a diode and connected with another transistor so that the base and the emitter is connected to the base and the emitter of the other transistor, respectively, thereby to constitute a partial current mirror. A plurality of the partial current mirrors thus constituted are serially connected between an input terminal and a reference terminal, and an output terminal is connected to the collector of a partial current mirror which is directly connected to the reference terminal. Transistors of the same polarity are used to obtain an output current larger than an input current. On the contrary, to obtain an output current smaller than an input current, the transistors constituting the partial current mirror directly connected to the reference terminal are made to have the opposite polarity to the transistors constituting other partial current mirrors.

A four-terminal integrated circuit high-frequency RF amplifier connects to external circuitry via a ground terminal, and RF input terminal, an RF output terminal and a DC biasing terminal. A two stage amplification architecture is employed--a current gain transistor (common-emitter) is cascoded with a subsequent voltage gain transistor (common-base) while yet maintaining RF signal inversion overall from input to output so as to increase stability. A biasing current-mirror transistor provides biasing current to the current-gain transistor. A fourth transistor connected as a forward-biased collector-base shorted diode between the current mirror biasing transistor and a common external biasing terminal supplies bias current to the current-mirror biasing transistor while simultaneously minimizing voltage swings across the current-gain transistor. The amplifier module has very low input capacitance which does not change appreciably with changes in load impedance, and operates with great stability under a wide range of different input and output conditions and RF frequencies. Because of its relative simplicity and compactness, the amplifier can be used to great advantage as an IC "building block" in a variety of different applications.

A transistor bias circuit is provided that is capable of operating from a power supply voltage that is slightly higher than twice the base-emitter voltage of the transistor to be biased. The bias circuit includes a transistor connected in a current-mirror configuration with the transistor to be biased. A feedback circuit maintains the mirrored current at a constant level. The gain of the feedback circuit is improved by the addition of a non-inverting amplifier within the feedback circuit. In a preferred embodiment, the biased transistor is concurrently in both a Darlington and the current mirror configuration. Moreover, a feedback transistor in the feedback circuit is also concurrently in the Darlington configuration, thus providing an efficient biasing arrangement for an amplifier block based on the Darlington arrangement.

There is disclosed a bias circuit exhibiting good stability over variations in temperature and power supply voltage and capable of generating a plurality of discrete levels of output current for biasing RF power amplifier. In accordance with the invention, the bias circuit includes (1) a master transistor connected to the slave transistor in a current-mirror configuration and having two parallel-connected transistor elements, (2) a switch connected to at least one transistor element to control its operation, and (3) a feedback circuit by which the voltage at the collector of the master transistor may be fed back to control the voltages at the bases of the master transistor and the slave transistor. Moreover, the bias circuit can be operated from a power supply voltage that is just above twice the value of the base-emitter voltage of the transistor in the circuit.