Transformer-Feedback Receiver Circuit for Linear RF Input Matching
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Solution Overview
Problem
The increasing demand for high receiver linearity in wireless communications, especially in devices like cellular phones, is challenged by the need to manage multiple frequency bands and strong interference while maintaining low noise and power consumption, with existing positive feedback architectures being non-linear and sensitive to instability.
Innovation Solution
A receiver circuit employing negative feedback through a transformer to combine a feedback signal with the input signal, using a mixer-first architecture with passive mixers and transimpedance amplifiers, allowing for adjustable and controllable input impedance to enhance linearity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If positive feedback architecture is used to control input impedance, then input impedance control is improved, but linearity deteriorates and stability becomes sensitive
Solution Approach 1:
The patent inverts the feedback approach by using negative feedback instead of positive feedback to control the input impedance of the mixer-first receiver. This inversion resolves the technical contradiction by maintaining the ability to control input impedance while simultaneously improving linearity and stability, directly addressing the drawbacks of positive feedback architectures.
Solution Approach 2:
The patent implements a feedback mechanism where a portion of the output signal is fed back to the input through a controlled path. This feedback structure enables dynamic control of the input impedance while maintaining system stability and linearity through the negative feedback loop, resolving the contradiction between impedance control and reliability.
2Reliability
If mixer-first architecture is used, then linearity is improved compared to LNA-first architecture, but noise performance deteriorates
Solution Approach 1:
The patent changes the operating parameters of the mixer-first architecture by implementing negative feedback control and optimizing the transimpedance amplifier parameters. This allows the system to achieve improved linearity while managing noise figure through parameter optimization, resolving the contradiction between linearity improvement and noise performance deterioration.
3Reliability
If high receiver linearity is provided to handle strong interference, then interference rejection is improved, but noise performance and power consumption worsen
Solution Approach 1:
The patent uses negative feedback to achieve high linearity for interference rejection while controlling the impact on noise figure. The feedback loop linearizes the receiver response to strong interferers without requiring excessive gain in the front-end amplifiers, thereby managing noise performance.
Solution Approach 2:
The patent applies partial feedback action where only a controlled portion of the output is fed back, sufficient to achieve the required linearity for interference rejection but not excessive to cause instability or degrade noise performance. This balanced approach resolves the contradiction between linearity and noise figure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves improved in-band and out-of-band linearity with reduced noise figure and power consumption, using a simple structure that optimizes input impedance for better interference rejection.
Implementation Method 1
The subtraction of the output signal of the feedback path with the received radio frequency signal is achieved by means of the transformer
Data Source
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AI summary
An example of a receiver circuit is disclosed. The receiver circuit comprises an input for receiving a radio frequency signal, an output for providing an output signal of the receiver circuit, a receive path, wherein the receive path is connected between the input and the output of the receiver circuit, and a feedback path, wherein an input of the feedback path is connected to the output of the receiver circuit. The receiver circuit also comprises a transformer, wherein an output signal of the feedback path is combined with the received radio frequency signal in the receive path to form a first signal. The receive path comprises a first mixer for downconverting the first signal by a local oscillator frequency, and an amplifier for amplifying the downconverted first signal. The feedback path comprises a second mixer for upconverting a signal in the feedback path by said local oscillator frequency. The combination of the output signal of the feedback path with the received radio frequency signal is achieved by means of the transformer.