Amplifier Feedback Bias Network for Out-of-Band Oscillation Control
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Solution Overview
Problem
Wireless communication devices face challenges in maintaining stability and preventing out-of-band oscillations due to dynamic antenna impedance changes, which cause reflections and potential violations of communication standards, with existing solutions being either ineffective or undesirable in terms of size and cost.
Innovation Solution
A wireless communication device amplifier is configured with a frequency-dependent feedback loop using small-sized resistors, inductors, and capacitors to selectively provide feedback, reducing out-of-band oscillations by adjusting the magnitude and phase of the feedback over frequency, and incorporating a biasing circuit that sinks current to maintain desired biasing and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large capacitor is used in the feedback loop to prevent out of band oscillations, then amplifier stability is improved, but the device size and integration difficulty increase
Solution Approach 1:
The patent changes the parameters of the feedback network by using small-value capacitors (e.g., 0.5pF to 5pF) combined with specific resistor values to achieve the same stability effect that would otherwise require a large capacitor. This transforms the solution from a single large capacitor to a network of small components with different electrical characteristics.
Solution Approach 2:
The patent segments the feedback function into multiple components (resistors and small capacitors) working together in a network, rather than relying on a single large capacitor. This segmentation allows each component to be small enough for integration while collectively providing the necessary stability.
2Object-generated harmful factors
If a large capacitor is used in the feedback loop to reduce out of band emissions, then oscillation suppression is improved, but manufacturing cost and integration feasibility worsen
Solution Approach 1:
The patent modifies the electrical parameters of the feedback network by selecting specific small values for capacitors and resistors that together provide the necessary frequency-dependent feedback to suppress out of band emissions, replacing the need for a single large capacitor that would be difficult to manufacture and integrate.
Solution Approach 2:
The feedback network using small components serves multiple functions: it provides frequency-dependent feedback to suppress out of band emissions, maintains amplifier stability, and enables integration on a single die, whereas a large capacitor could only provide basic feedback but failed at integration.
3Reliability
If feedback is increased to prevent oscillations, then amplifier stability is improved, but the complexity of the feedback network increases
Solution Approach 1:
The patent achieves the desired feedback effect by optimizing the parameters of a relatively simple network consisting of a capacitor in parallel with a series combination of resistors, rather than requiring a complex multi-component network. The specific parameter values are selected to provide frequency-dependent feedback with minimal components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively stabilizes the amplifier and reduces out-of-band oscillations, preventing unwanted emissions while allowing for integration into a single die without the need for large capacitors, thus addressing the limitations of prior art.
Implementation Method 1
a feedback loop selectively passes, on a frequency dependent basis, a portion of the amplified signal through amplifier feedback loop to the amplifier input
Implementation Method 2
The biasing device draws current from the biasing node while providing the biasing voltage to the output amplifier
Data Source
AI summary
A wireless communication device output amplifier configured to reduce or eliminate out of band oscillations from voltage standing waves generated by antenna impedance mismatch reflection. The amplifier is configured with an input, output, and biasing node. The biasing node is configured to receive a biasing signal from a biasing amplifier. The biasing amplifier draws current from the biasing node while providing the biasing voltage to the output amplifier. To reduce or eliminate out of band voltage standing waves from antenna reflections, a frequency dependant network is provided as a feedback loop to selectively provide feedback to the output amplifier to reduce or eliminate unwanted out of band oscillations, such as voltage standing waves. The frequency dependant network may comprise one or more resistors, inductors, and capacitors which are of small size and may be integrated.