RF Receiver LNA Passive Mixer DC Voltage Control
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Solution Overview
Problem
Current RF receivers face challenges in detecting weak in-band signals due to insufficient linearity caused by strong out-of-band jammers, and the use of SAW filters increases costs and circuit board space, especially with the need for compatibility across various frequency bands.
Innovation Solution
A receiver design that eliminates AC coupling capacitances between the low noise amplifier (LNA) and passive mixer, incorporating a passive mixer and filter, and a baseband processing block with a transimpedance amplifier, which maintains nodes at a common DC voltage to enhance linearity and dynamic range without the need for SAW filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a SAW filter is used to improve linearity and reject out-of-band jammers, then the rejection ratio improves, but the in-band attenuation increases and cost increases
Solution Approach 1:
The patent extracts and removes the AC coupling capacitances from the signal path between LNA and mixer stages. This elimination prevents the capacitances from causing DC offset voltages and in-band signal attenuation, thereby improving weak signal detection capability while maintaining jammer rejection through the passive mixer architecture
Solution Approach 2:
The patent replaces expensive SAW filters with an integrated passive mixer architecture that can be implemented using standard CMOS or BiCMOS processes. This substitution eliminates the need for additional discrete SAW filter components, reducing both cost and circuit board area while achieving the required linearity and jammer rejection
2Object-affected harmful factors
If SAW filters are used to meet linearity requirements, then jammer rejection improves, but circuit board area increases and cost increases
Solution Approach 1:
The patent merges the functions of the LNA and mixer stages into a tightly integrated architecture where the passive mixer is directly coupled to the LNA output without AC coupling capacitances. This integration eliminates the need for separate SAW filter components, reducing circuit board area while maintaining linearity and jammer rejection through the combined circuit design
Solution Approach 2:
The passive mixer architecture serves multiple functions simultaneously: it provides frequency conversion, rejects out-of-band jammers through its inherent filtering properties, and eliminates the need for separate SAW filters. This multi-functionality reduces the overall component count and circuit board area requirement
3Stability of the object's composition
If AC coupling capacitances are used between LNA and mixer, then DC isolation is provided, but DC offset voltages are generated and linearity deteriorates
Solution Approach 1:
The patent extracts and removes the AC coupling capacitances from the signal path between LNA and mixer stages. This elimination prevents the capacitances from causing DC offset voltages and in-band signal attenuation, thereby improving weak signal detection capability while maintaining jammer rejection through the passive mixer architecture
Solution Approach 2:
The patent introduces a voltage controller as an intermediary element that actively maintains the first and second nodes at a common DC voltage level. This mediator prevents DC offset voltages from developing while allowing direct coupling between stages, achieving both DC stability and improved linearity
Data Source
AI summary
A receiver includes a low noise amplifier (LNA), a passive mixer, a passive filter, a baseband processing block and a voltage controller. The LNA receives and amplifies a radio frequency (RF) signal. The passive mixer is coupled to the LNA without any AC coupling capacitance therebetween, and generates an intermediate frequency signal by down-converting the RF signal. The passive filter filters the intermediate frequency signal. The baseband processing block includes a transimpedance amplifier (TIA) and processes the filtered intermediate frequency signal. The voltage controller keeps a first node and a second node of a signal path to be around a common DC voltage, wherein the first node is located between an output terminal of the LNA and an input terminal of the passive mixer, and the second node is located between an output terminal of the passive mixer and an output terminal of the TIA.