RF Amplifier Bias Boosting via Self-Regulating Current Mirror
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Solution Overview
Problem
Conventional RF amplifiers face challenges in maintaining linearity at higher output power levels due to increased average bias supply current, leading to saturation and nonlinear output signals, and existing bias boosting techniques require additional components for accurate quiescent current control.
Innovation Solution
The RF amplifier employs a self-bias boosting mechanism using a dual current mirror circuit with a discharge transistor and power transistor, along with a current source and capacitors, to control quiescent current and maintain optimal biasing, allowing operation in class AB mode without additional resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the RF amplifier is biased for class AB operation to achieve higher power-added efficiency, then the power-added efficiency is improved, but the average bias supply current increases as the RF input power increases, leading to increased voltage drop across resistive components and pushing the amplifier into class B or class C operation which causes output signal nonlinearity
Solution Approach 1:
The RF amplifier automatically adjusts its own bias voltage through the interaction of the amplifying transistor's base-emitter junction and the parallel RC circuit. As the amplifier operates and current increases, the circuit self-regulates by allowing the capacitive reactance to decrease, which compensates for the voltage drop and maintains the bias point, eliminating the need for external bias boosting components
Solution Approach 2:
The patent changes the impedance characteristics of the biasing circuit by introducing a parallel RC circuit where the capacitive reactance varies with frequency and operating conditions. This dynamic parameter change allows the circuit to adapt to varying RF input power levels, maintaining optimal bias conditions across different operating points without requiring additional resistors or complex current mirror circuits
2Measurement precision
If prior-art techniques use a cascode current mirror circuit or modified Wilson current mirror circuit to provide bias boosting, then the quiescent current control is improved, but additional resistors are required to achieve accurate control due to necessary isolation between RF and biasing circuits
Solution Approach 1:
The patent merges the RF amplifying transistor with the biasing circuitry by using the same transistor (Q1) as both the amplifying element and part of the bias control mechanism. The base-emitter junction of the amplifying transistor itself becomes part of the bias network, eliminating the need for separate current mirror circuits and isolation resistors that would otherwise be required to control quiescent current accurately
3Reliability
If a stacked diode circuit with a capacitor is used for bias boosting, then the linearity at higher output power levels is improved, but the difficulty of achieving sufficient control of the quiescent current increases since the stacked diode circuit does not form a current mirror circuit
Solution Approach 1:
The circuit uses the amplifying transistor's own base-emitter junction as the biasing element, which automatically regulates the quiescent current based on the transistor's inherent characteristics. This self-regulating mechanism provides both the linearity improvement of stacked diode circuits and the precise quiescent current control of current mirror circuits, without requiring either additional diodes or complex mirror configurations
Data Source
AI summary
The present invention provides methods and apparatuses for an amplifier circuit for amplifying an input signal. An amplifier circuit for amplifying an input signal comprises an amplifying transistor circuit having a power transistor and a dc bias circuit having a plurality of current mirror circuits and a discharge transistor wherein the discharge transistor and the power transistor form a combined current mirror circuit to control quiescent current in the power transistor.