An amplifier circuit (1) includes an amplifying transistor (QO) and an impedance-controllable dc bias circuit (2) for biasing the amplifier transistor (QO) to obtain a conduction angle of at least about 180.degree.. The dc bias circuit (2) includes a self-bias boosting circuit having separate current sources (Ibias, Iclass) for independently controlling the output impedance of the dc bias circuit (2) and the quiescent current of the amplifier transistor (QO), and has a Wilson current-mirror (Q4, Q5, Q6, Q7) integrated with a cascode current-mirror circuit (Q2, Q3, Q8) to form an extended Wilson current-mirror circuit (Q2-Q8) having an output coupled to a control terminal of the amplifying transistor (QO) by a resistor (R1), and a capacitor (C2) coupled from the extended Wilson current-mirror circuit (Q2-Q8) to a common terminal (Gnd).
CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. provisional application Ser. No. 60/431,840 filed Dec. 9, 2002, which is incorporated herein by reference.
A biasing circuit adapted for operative coupling to the first input terminal so as to provide a relatively high biasing impedance to ground at the first input terminal, said biasing circuit being adapted to controllably vary the DC-voltage signal which biases the transistor amplifier, whilst at least one component of the biasing circuit is configured to simultaneously form a low-pass circuit for filtering a noise component of the DC-voltage signal before the DC-voltage signal is provided to the first input terminal.
Provided is circuitry for biasing a transistor amplifier with a DC-voltage signal, the transistor amplifier having a first input terminal, a second input terminal, and an output terminal coupled to the second input terminal. The circuitry includes a sensor capacitor connected to the first input terminal and an impedance transistor arranged in parallel with said capacitor, the transistor and capacitor forming a low-pass filter. The circuitry also includes a biasing circuit configured to controllably vary a DC-voltage signal for operatively biasing the amplifier, the biasing circuit including a cascaded current arrangement configured to subdivide a reference current into smaller currents for selectively generating voltage potentials for biasing the impedance transistor to adjustably filter a noise component of the DC-voltage signal via the low-pass filter before the DC-voltage signal is provided to the first input terminal.
