Stepped Gain Mixer With Passive Switching for Stable Receiver SNR
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Solution Overview
Problem
Existing wireless communication receivers face limitations in achieving high signal-to-noise ratios over a large gain control range, especially in OFDM systems, and consume excessive power due to the use of series-configured low noise amplifiers, which restricts data throughput and efficiency.
Innovation Solution
A passive mixer device with eight transistors and three switches operates in two modes to provide a stepped gain control, utilizing fine gain steps and avoiding series-configured low noise amplifiers, maintaining a high signal-to-noise ratio over a 35 dB gain range while reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If series-configured low noise amplifiers are used to achieve high signal-to-noise ratio, then signal-to-noise ratio is improved, but power consumption increases
Solution Approach 1:
The receiver front end is segmented into parallel LNA paths instead of a single series chain. Multiple LNAs operate in parallel with independent gain control, allowing the system to achieve high signal-to-noise ratio when needed while consuming less power during normal operation by using only the necessary number of active amplifiers.
Solution Approach 2:
The system dynamically adjusts the number of active LNA paths based on signal strength and required gain. The gain control mechanism enables transitions between different operational states (0, 1, 2, or more LNAs active), optimizing the balance between signal-to-noise ratio and power consumption in real-time.
2Device complexity
If few large gain steps are used in the receiver, then device complexity is reduced, but signal-to-noise ratio becomes inconsistent (zig-sag) over the gain range
Solution Approach 1:
The gain control is segmented into multiple independent LNA paths, each contributing a portion of the total gain. This segmentation allows the system to achieve fine-grained gain adjustment (e.g., 0 dB, 3 dB, 6 dB, 9 dB steps) by selectively activating different combinations of parallel LNAs, ensuring consistent signal-to-noise ratio across the entire gain range without requiring a single complex high-gain amplifier.
3Use of energy by moving object
If parallel low noise amplifier paths are used instead of series configuration, then power consumption is reduced, but achieving high signal-to-noise ratio over large gain range becomes more difficult
Solution Approach 1:
Multiple parallel LNA paths are merged at the output stage, combining their contributions to achieve the required total gain and signal-to-noise ratio. The parallel configuration allows the system to merge only the necessary number of amplifier paths based on current signal conditions, reducing power consumption while maintaining performance through selective combination rather than always using all paths or requiring a series configuration.
Data Source
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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.