Abstract: An K-band amplifier circuit (10) with two samplers (12, 18) coupled to detectors (22, 26) that detect an input and an output RF signal level. These two reference signals are provided to a differential gain control circuit (24) which is coupled to one or more variable gain amplifier (VGA) (14) stages. The VGAs compensate for the gain of an entire chain of amplifiers (16). When the individual amplifier gains vary for any reason, (i.e., process, temperature effects or end of life degradation) the variation in gain causes higher or lower levels of detected output reference signals for a given RF input signal. The gain control circuit (24) drives the VGA (14) up or down as appropriate. By maintaining a constant offset in input and output reference control signals, the gain control circuit (24) drives the amplifier chain (16) to a constant gain.

Abstract: An active bias compensation circuit (110) senses a quiescent current flowing in an amplifier (130) and adjusts the quiescent current to maintain an optimal DC biasing of the amplifier (130) over a wide range of factors, e.g., temperature variation, process variation, history of the amplifier (130), etc. The compensation circuit (110) includes two transistors (101, 102) forming a difference amplifier. A sensing voltage proportional to the quiescent current and a reference voltage are applied to the base electrodes of the two transistors (101, 102), which generates a bias signal in response to a difference between the sensing voltage and the reference voltage. The bias signal adjusts the quiescent current in the amplifier (130).

Abstract: A harmonic generator (20) converts an input signal (24) at a fundamental frequency (28) into an output signal (32) at a harmonic frequency (34). A non-linear device (22) converts the input signal (24) into an intermediate signal (38) in which the harmonic frequency (34) has a maximized amplitude (40) determined by a conduction angle (26). A harmonic filter (68) produces a filtered signal (70) proportional to the amplitude (40) of the harmonic frequency (34) within the intermediate signal (38). A detector (80) produces a control signal (82) proportional to the amplitude of the filtered signal (70). A control circuit (84) produces a variable bias signal (50) for non-linear device (22), bias signal (50) being proportional to the amplitude of the control signal (82) and determining the conduction angle (26). An output filter (88) converts the intermediate signal (38) into an output signal (32) at the harmonic frequency (34).

Abstract: A power amplifier (10) suitable for satellite cellular communication systems provides highly efficient linear amplification of noise-like RF signals that have multiple carriers spread over a large instantaneous bandwidth. The amount of distortion present in the output is detected (14, 16, 18) and a feedback signal is provided to control the bias point of the active devices. As drive levels increase, the increased harmonic distortion power detected causes the power amplifier bias to increase thus reducing distortion. The control circuit (20) continually re-biases the power amplifier (12) for maximum efficiency for a predetermined level of distortion. The control circuit (20) may be adjusted to maximize efficiency while maintaining an allowable distortion level over the entire dynamic range of the devices.