Source Injection Mixer With Short Stub for Higher Conversion Gain
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Solution Overview
Problem
Conventional source injection mixers suffer from low conversion gain, particularly at high frequencies due to the inductance effects of the shorting stub used in the source of the transistor, which limits their performance in high-speed wireless systems.
Innovation Solution
The source injection mixer design incorporates a shorting stub shorter than ¼ of the electrical length at the LO frequency, along with an LO matching circuit that matches the impedance of the LO port and source, and an RF matching circuit that matches the impedance of the RF port and drain, to minimize inductance effects and enhance conversion gain. Additionally, the LO matching circuit is configured with a transmission line and capacitive elements to achieve a lower impedance, allowing for improved frequency dependency and increased conversion gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional source injection mixer uses a shorting stub at the source of the transistor, then isolation between ports is improved, but conversion gain deteriorates at high frequencies due to inductance effects
Solution Approach 1:
The patent changes the electrical length parameter of the shorting stub from the conventional ¼ wavelength to a shorter length (less than ¼ wavelength) at the LO frequency. This parameter modification reduces the inductance effect of the stub while maintaining its isolation function, thereby improving conversion gain at high frequencies without sacrificing port isolation
Solution Approach 2:
The patent applies preliminary anti-action by introducing a compensation capacitor in parallel with the shorting stub. This capacitor pre-compensates for the harmful inductance effect of the stub, canceling out its negative impact before it degrades conversion gain, thus maintaining high performance across the frequency range
2Power
If the shorting stub is made shorter to reduce inductance effects, then conversion gain is improved, but the isolation function may deteriorate
Solution Approach 1:
The patent merges two functions into a single component: the shorting stub simultaneously provides both the isolation function (by being shorted to ground) and the inductance compensation function (by being shorter than conventional length). This combined approach maintains port isolation while reducing harmful inductance effects, improving conversion gain without requiring additional components
3Power
If active mixers are used to achieve high conversion gain, then frequency conversion performance is improved, but LO signal leakage to IF terminal increases
Solution Approach 1:
The patent applies local quality by using a source injection configuration where the LO signal is applied to the source terminal rather than the gate. This creates different electrical characteristics at different terminals: the source terminal provides high conversion gain while the gate terminal maintains good isolation properties, locally optimizing both gain and leakage suppression in different parts of the circuit
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
This configuration significantly improves the conversion gain of the source injection mixer, reducing the impact of inductance and maintaining high performance even at high IF signal frequencies, thereby addressing the limitations of conventional designs.
Implementation Method 1
the inductance effects of the shorting stub used in the source of the transistor, which limits their performance in high-speed wireless systems
Implementation Method 2
an LO matching circuit that is inserted between an LO port where the LO signals are input and the source of the transistor, and that matches impedance of the LO port and impedance of the source as viewed from the LO port
Implementation Method 3
an RF matching circuit that is inserted between an RF port where RF signals are output and a drain of the transistor, and that matches impedance of the RF port and impedance of the drain as viewed from the RF port
Implementation Method 4
The LO matching circuit is configured with a transmission line and capacitive elements to achieve a lower impedance, allowing for improved frequency dependency and increased conversion gain
Data Source
AI summary
A source injection mixer includes an FET, an IF matching circuit between an IF port and a gate of the FET, and that matches impedance of the IF port and impedance of the gate as viewed from the IF port, a shorting stub of which one end is connected to a source of the FET and another end is grounded, and shorter than ¼ of an electric length at a frequency of LO signals, an LO matching circuit between an LO port and the source of the FET, and that matches impedance of the LO port and impedance of the source as viewed from the LO port, and an RF matching circuit between an RF port and a drain of the FET, and that matches impedance of the RF port and impedance of the drain as viewed from the RF port.