Passive RF Mixer Isolation Stage for Lower Noise and Power
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Solution Overview
Problem
Current radio frequency mixing apparatus in communication devices, such as cellular and GPS receivers, face challenges in achieving low noise figures, reduced size, weight, and power consumption, while existing solutions often compromise on these criteria.
Innovation Solution
A passive mixing apparatus is designed with a low noise amplifier, transformer block, radio frequency transconductance stage, mixing core, and transimpedance amplifier, incorporating a high output impedance isolation stage to mitigate noise contribution and reduce power consumption, featuring a CMOS mixing core and common-gate devices for improved impedance matching and isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional mixing apparatus are used, then mixing function is achieved, but noise figure is high and power consumption is excessive
Solution Approach 1:
The mixing apparatus is divided into distinct functional stages: a first mixing stage that performs initial downconversion, and a second mixing stage that completes the downconversion to baseband. This segmentation allows each stage to be optimized independently, with the first stage using a switched capacitor mixer for low power and the second stage using a switched current mixer for low noise, thereby resolving the contradiction between noise figure and power consumption
Solution Approach 2:
Different mixing topologies are applied to different stages based on their specific requirements. The first mixing stage employs a switched capacitor mixer topology optimized for low power consumption, while the second mixing stage uses a switched current mixer topology optimized for low noise figure. This local optimization of quality characteristics at different stages resolves the contradiction by allowing each stage to excel at its primary function
2Area of stationary object
If mixer size is reduced for compact devices, then device footprint decreases, but noise performance deteriorates
Solution Approach 1:
The patent combines multiple mixing functions into a single integrated apparatus that performs both the first downconversion and the second downconversion to baseband. By merging the two mixing stages and their associated components into one compact unit, the overall mixer area is reduced while maintaining the noise performance benefits of the two-stage architecture
Solution Approach 2:
The second mixing stage is nested within the overall mixing apparatus structure, with the output of the first mixing stage feeding directly into the second mixing stage. This nested arrangement allows compact integration of multiple functional elements, reducing the total area while preserving the noise performance advantages of the cascaded mixing stages
3Ease of operation
If impedance matching is optimized for low input impedance, then signal coupling improves, but isolation between stages deteriorates
Solution Approach 1:
An intermediate filtering stage is introduced between the first and second mixing stages. This intermediary element provides frequency selection and isolation, allowing the first stage to maintain low input impedance for good signal coupling while the intermediate filter prevents noise and unwanted signals from coupling into the second stage, thereby maintaining stage isolation
Data Source
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AI summary
A noise isolation passive mixing apparatus is designed to mitigate noise contribution from intermediate frequency (IF) filters and amplifiers in a radio frequency translation stage. Common-gate configuration devices are inserted between passive mixer output and input of a transimpedance amplifier. In this way, circulation of the input-referred noise of the transimpedance amplifier is decreased, because of the relatively high output impedance of the common-gate devices, and the noise figure of the mixing apparatus can be improved. Since the radio frequency signal still sees low impedance, a radio frequency transconductance (RF gm) stage can be removed from the mixing apparatus, reducing current consumption. A double-balanced mixing apparatus with this general architecture may be implemented in a 0.18 micrometer CMOS technology and used in a low-IF global positioning system operating at 1.575GHz, in an access terminal of a cellular communication system, and in other systems.