Embedded Passive Mixer Filtering for SAW-Less Zero-IF Receivers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Zero-IF radio frequency receivers in cellular systems face challenges with transmitter leakage and noise floor issues due to the need for external SAW filters, which degrade noise figure and increase power consumption, and existing SAW-less solutions suffer from performance problems like noise figure degradation and varying rejection.
Innovation Solution
A mixer circuit with integral passive low-pass filtering circuitry for RF signal processing, eliminating the need for external SAW filters by incorporating a first switching stage for frequency conversion and a second switching stage for noise suppression, achieving highly linear mixing and noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an external SAW filter is used after the LNA stage, then transmitter leakage rejection and Triple Beat performance are improved, but noise figure increases and power consumption increases
Solution Approach 1:
The patent combines the mixer and low-pass filter into a single integrated mixer-filter structure. The filtering function is embedded within the mixer circuitry itself, eliminating the need for separate external SAW filters. This integration achieves transmitter leakage rejection and Triple Beat performance improvement while reducing power consumption and noise figure compared to external filter solutions
Solution Approach 2:
The mixer-filter structure performs multiple functions simultaneously: frequency conversion (mixing) and signal filtering. The same circuit elements used for mixing also provide the low-pass filtering function, making the structure multi-functional and eliminating the need for separate filtering components that would increase power consumption
2Object-affected harmful factors
If an external SAW filter is used after the LNA stage, then transmitter leakage rejection and Triple Beat performance are improved, but device size increases and manufacturing complexity increases
Solution Approach 1:
The patent integrates the low-pass filter function directly into the mixer circuit, combining what would traditionally be separate components into a single unified structure. This reduces device complexity and eliminates the need for external SAW filters and matching components, while maintaining effective transmitter leakage rejection
Solution Approach 2:
The patent extracts the filtering function from separate external components and embeds it within the mixer circuitry itself. This extraction and integration approach simplifies the overall device structure by removing external filtering components and their associated matching networks
3Object-affected harmful factors
If a Tx canceller with LMS adaptive filter is used, then transmitter leakage rejection is improved, but noise figure degrades and system complexity increases
Solution Approach 1:
The mixer-filter structure provides self-service by inherently providing both mixing and filtering functions through its own circuitry. The embedded low-pass filter automatically rejects transmitter leakage and noise without requiring external adaptive filtering circuits, maintaining low noise figure while achieving effective leakage rejection
Data Source
AI summary
A communication channel has a highly linear switched current mixer that incorporates passive filtering (e.g., low pass, notch) for improved transmitting (Tx) and receiving (Rx) with adding external filtering components. A high IIP2 (input referenced second order intercept point) of the receiver at the Tx offset is essential to avoid corrupting the system's sensitivity performance, and a high triple beat (TB) is required to avoid sensitivity degradation due to transmitter leakage. Thanks to the embedded filtering in the mixer and the active post-distortion (APD) method in a low noise amplifier (LNA), the required high linearity is achieved with low noise figure and power consumption, overcoming transmitter power leakage without the use of a SAW (surface acoustic wave) filter.