Stepped Gain Mixer Circuit for Wide-Range SNR and Linearity
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Solution Overview
Problem
Conventional wireless communication receivers face limitations in achieving high signal-to-noise ratios (SNR) over a large gain control range, particularly in OFDM systems, and consume excessive power due to the use of series-configured low noise amplifiers (LNAs).
Innovation Solution
A receiver design incorporating an amplified stepped gain mixer portion with low-noise amplifiers and stepped gain mixers, which operates in multiple gain states to maintain a smooth SNR over a wide dynamic range, utilizing passive mixers and avoiding series-configured LNAs to reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If series-configured low noise amplifiers (LNAs) are used to achieve high signal-to-noise ratio, then SNR is improved, but power consumption increases
Solution Approach 1:
The receiver front end is divided into multiple parallel LNA paths (first LNA, second LNA, third LNA) instead of using a single series configuration. Each LNA operates at different gain levels, allowing the system to achieve high SNR when needed while consuming less power during normal operation by selectively activating only the necessary number of LNAs.
Solution Approach 2:
The system dynamically adjusts the number of active LNAs based on signal conditions. The controller selectively enables or disables specific LNA paths to match the required gain level, transitioning from static series configuration to dynamic parallel operation, thereby optimizing the trade-off between SNR and power consumption.
2Device complexity
If a receiver uses few large gain steps to cover a large gain range, then device complexity is reduced, but signal-to-noise ratio deteriorates due to zig-sag SNR
Solution Approach 1:
The gain control is segmented into multiple independent LNA paths, each providing a specific gain level. Instead of using a single variable gain controller with few large steps, the system uses multiple discrete LNA stages that can be selectively combined, achieving fine-grained gain control (reducing zig-sag SNR) while maintaining relatively simple individual LNA designs.
Solution Approach 2:
Multiple LNA paths with different gain characteristics are merged in parallel, allowing the system to achieve a wide gain range with fine resolution by selectively activating combinations of LNAs. This combining approach provides smooth SNR across the gain range without requiring each individual LNA to be overly complex.
3Reliability
If high gain is used to improve signal-to-noise ratio, then SNR is improved, but saturation occurs in the presence of jammer interference
Solution Approach 1:
The system dynamically selects the appropriate LNA gain level based on signal conditions. When jammer interference is detected, the controller switches to lower-gain LNA paths to prevent saturation, while maintaining high SNR for weak signals by using higher-gain paths when appropriate. This dynamic adaptation resolves the contradiction between needing high gain for SNR and avoiding saturation from interference.
Solution Approach 2:
The system changes the gain parameter by selectively activating different LNA paths with predetermined gain levels. This provides discrete, controlled gain adjustments that allow the receiver to adapt to varying signal conditions, including the presence of jammer interference, without requiring continuous gain control or complex adaptive algorithms.
Data Source
AI summary
An amplified stepped gain mixer portion improves the signal-to-noise ratio of a receiver by using multiple gain states to improve linearity. The mixer portion includes an amplifier, a switch and two transistors. The amplifier output is coupled to the sources of the two transistors. An oscillating signal is present on the transistor gates. The transistor drains are coupled to one another through the switch when the switch is closed. The mixer portion operates in two modes. In a 1/2 mode, the mixer portion output current flows only through the first transistor and not through the second transistor because the switch is open. In a 2/2 mode, the mixer portion output current flows through both transistors. The mixer portion is configured such that the switch is closed when a switching signal is asserted. The switching signal is asserted when a bit of a mixer control register is written to.