Frequency-Selective LNA Feedback for Power Supply Noise Rejection
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Solution Overview
Problem
Conventional low-noise amplifier (LNA) architectures struggle to meet stringent requirements for gain, bandwidth, linearity, and output impedance matching, particularly in advanced RF communication bands such as 5G mobile network bands and millimeter wave ranges, due to limitations in power supply rejection and noise handling.
Innovation Solution
The implementation of a frequency-selective input matching feedback circuit with a power supply rejection resistor and adjustable capacitors and resistors to improve power supply rejection and reduce non-linearities caused by low-frequency noise, allowing for multiple gain modes and enhanced settling times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LNA architecture is used, then device simplicity is maintained, but power supply rejection is insufficient and noise handling is poor
Solution Approach 1:
A feedback network is introduced as an intermediary between the input terminal and the output terminal of the LNA. This feedback network includes a feedback resistor connected between the output terminal and input terminal, along with associated capacitors and resistors that form a frequency-selective feedback path. The feedback network mediates the signal flow to improve power supply rejection ratio while managing noise characteristics, resolving the contradiction between reliability improvement and device complexity.
2Reliability
If feedback circuit is added to improve power supply rejection, then power supply rejection ratio is improved, but low-frequency noise is coupled to the input
Solution Approach 1:
The feedback network is designed with frequency-selective components that provide different characteristics at different frequency ranges. Capacitors are strategically placed within the feedback path to create frequency-dependent impedance, allowing the network to reject power supply noise at certain frequencies while attenuating low-frequency noise through the feedback mechanism. This local quality differentiation resolves the contradiction by treating different frequency components differently.
Solution Approach 2:
The feedback network converts the potentially harmful low-frequency noise that would otherwise be coupled to the input into a beneficial effect. By introducing the feedback path with appropriate frequency-selective components, the circuit uses the noise signal itself as feedback to suppress its own noise coupling, transforming the harmful effect into a noise-reduction mechanism that improves overall signal quality.
Data Source
AI summary
Frequency-selective feedback circuits and methods for an amplifier (particularly LNAs) that improve power supply rejection in feedback circuits, reduce non-linearities caused by low-frequency noise coupled to the input of the LNA, and improve settling times of the quiescent bias-point of the LNA. Some embodiments allow multiple modes of operation to allow selection of gain versus linearity characteristics. One aspect of the present invention includes an input matching feedback circuit configured to be coupled between an input terminal of an amplification core and a feedback node in the output signal path of the amplification core, the input matching feedback circuit including a power supply rejection resistor configured to provide a low-impedance path to a reference potential for low-frequency noise.