Quadrature Frequency Doubler with Tunable Phase Offset
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Solution Overview
Problem
Full-duplex RF front-ends in WLAN networks face issues with receive desensitization and transmit error vector magnitude (EVM) degradation due to receiver local oscillator (LO) leakage, and existing frequency doubling circuits introduce amplitude mismatch and quadrature phase offset between quadrature signals.
Innovation Solution
A frequency doubler circuit comprising an adder block and two mixer blocks that produce in-phase and quadrature signals with minimal phase error, using a phase shifter to further reduce errors, and employing a two-stage polyphase filter to ensure equal loading and minimize phase offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a state-of-the-art frequency doubling circuit is used, then frequency doubling function is achieved, but amplitude mismatch and quadrature phase offset are introduced between quadrature signals
Solution Approach 1:
The frequency doubler is divided into multiple independent mixer stages (first mixer producing in-phase signal, second mixer producing quadrature signal) with separate signal paths. Each mixer processes specific input combinations independently, allowing precise control over amplitude and phase characteristics of each quadrature component without mutual interference
Solution Approach 2:
Different input signal combinations are applied to each mixer to optimize local signal characteristics. The first mixer uses specific in-phase and quadrature inputs while the second mixer uses different combinations, ensuring that each stage contributes optimally to the overall amplitude balance and phase accuracy of the output quadrature signals
2Productivity
If receiver local oscillator leakage is present in full-duplex systems, then transmit and receive operations can occur simultaneously, but receive desensitization and transmit EVM degradation occur
Solution Approach 1:
The circuit converts the potentially harmful LO leakage into a useful function by using the same LO signal that causes leakage to also drive the frequency doubler. The carefully controlled quadrature signal generation ensures that the leaked signal maintains proper amplitude and phase relationships, actually improving image rejection and allowing simultaneous TX/RX operation without the usual performance penalties
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 produces quadrature signals with substantially equal amplitude and minimal phase error, improving receiver performance by reducing amplitude mismatch and phase offset, thereby enhancing transmission quality in full-duplex systems.
Implementation Method 1
A voltage controlled oscillator (VCO) 100 is used to create a differential sinusoidal output 101 and 102
Implementation Method 2
These signals are input into a polyphase filter 110, which is an arrangement of resistors and capacitors interconnected in such a way so as to produce two quadrature differential outputs
Implementation Method 3
In mixer 130, the cos(ωt) terms are multiplied together, yielding cos(2ωt)
Data Source
AI summary
The present invention provides an improved frequency doubling circuit, with adjustable phase offset. Briefly, rather than using the traditional equations cos (2ωt)=cos 2(ωt)−sin 2(ωt) and sin(2ωt)=2 sin(ωt)cos(ωt), the quadrature output signals are generated utilizing mixers, each having two input signals, separated in phase by the same offset. This minimizes the effects of the non-linearities introduced by the mixer, which therefore reduces amplitude mismatch between the quadrature signals. Also, the phase offset of the quadrature output signals can be tuned and calibrated using a phase shifting circuit. This phase shifting circuit realizes a tuning range of approximately 5° in programmable steps. This combination of circuits can be used to minimize the amplitude mismatch and phase errors, thereby reducing the amplitude of and interference caused by transmission of the image frequency to the receivers input.