Single-Ended LNA Bias Filtering for High PSRR
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Solution Overview
Problem
Existing low-noise amplifiers (LNAs) face challenges in achieving high power supply rejection ratio (PSRR) and efficiency, particularly in the mega-Hertz range, due to difficulties in filtering power supply noise, leading to the preference for fully-differential designs over single-ended ones.
Innovation Solution
A low-noise amplifier design with a triple-stage isolation and low-voltage bias scheme using N-channel MOS transistors, incorporating lowpass and bandpass filters, and a current reuse mechanism to enhance PSRR, achieving a high PSRR of over 80 dB and improved power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If single-ended LNA implementation is used to achieve lowest noise and highest energy efficiency, then noise performance and power efficiency are improved, but power supply noise filtering becomes difficult in lower frequency ranges
Solution Approach 1:
A power supply rejection network is introduced as an intermediary component between the power supply and the LNA circuit. This network acts as a mediator that filters power supply noise before it reaches the sensitive LNA stages, enabling single-ended implementation to achieve both high efficiency and good noise rejection without requiring fully-differential architecture
2Object-affected harmful factors
If fully-differential LNA design is used to filter power supply noise, then power supply rejection ratio is improved, but device complexity and loss of single-ended efficiency increase
Solution Approach 1:
The LNA is divided into multiple stages with distinct functions: a first LNA stage for initial signal amplification, a second LNA stage for further amplification, and intermediate power supply rejection networks between stages. This segmentation allows each stage to be optimized independently, achieving high overall PSRR while maintaining single-ended simplicity and efficiency
3Object-affected harmful factors
If multiple LNA stages with power supply rejection networks are used to achieve high PSRR, then power supply rejection ratio is improved, but device complexity increases
Solution Approach 1:
The power supply rejection networks are designed to continuously operate across multiple frequency ranges, maintaining effective noise rejection throughout the entire signal bandwidth. The cascaded multi-stage architecture ensures continuous amplification and noise filtering action, achieving high PSRR without requiring overly complex individual stages
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 design achieves a high PSRR of greater than 80 dB and low power consumption while maintaining low noise, with the ability to implement higher-order filters and fast startup, utilizing a simple amplification element and current reuse for efficient amplification.
Implementation Method 1
a lowpass filter circuit coupled between the power supply node and ground
Implementation Method 2
a bandpass filter circuit coupled in series between the power supply node and ground
Data Source
AI summary
A low-noise amplifier includes a low-noise amplifier stage and a filtering and biasing stage. The low-noise amplifier stage receives an input signal and provides a first output signal in response thereto. The low-noise amplifier stage includes a gain element for proving the first output signal, and at least one lowpass filter circuit in series between a first power supply voltage terminal and the gain element having a conductivity determined by lowpass filtering a signal at a bias terminal, and a filtering and biasing stage having an input for receiving the first output signal, and an output for providing a second output signal, and at least one cascode element having a first current conduction path coupled in series between the bias terminal and the output, and having a predetermined filter characteristic.