Mixer Circuit Harmonic Rejection Using LC Source and Output Filters
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Solution Overview
Problem
Designing mixers for electronic devices with wireless communications capabilities is challenging due to the difficulty in suppressing harmonic conversion gain, which leads to undesired in-band spurs and degrades performance.
Innovation Solution
Incorporating passive LC filters at the source terminals of mixer transistors, active quality factor boosting circuits, and output notch filters to suppress third harmonic conversion gain, thereby reducing undesired in-band emissions without significant area or power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional mixer circuits are used without harmonic rejection filters, then the circuit complexity is low, but harmonic conversion gain produces undesired in-band spurs that degrade performance
Solution Approach 1:
The patent introduces LC filter circuits as intermediary elements between the mixer transistors and the output. These filters act as mediators that selectively reject harmonic conversion gain while allowing the fundamental frequency to pass through, thereby improving mixer performance without requiring complete redesign of the mixer core architecture.
Solution Approach 2:
The harmonic rejection function is segmented into separate LC filter circuits that are coupled to specific nodes within the mixer. Rather than attempting to solve the harmonic rejection problem in the mixer core itself, the patent divides the system into functional segments where filters are placed at strategic locations (source terminals and output nodes) to address harmonic issues locally.
2Reliability
If multiple filter circuits are added to suppress harmonic conversion gain, then harmonic rejection improves, but the area and component count increase
Solution Approach 1:
The patent combines multiple filtering functions into shared LC filter circuits that serve multiple purposes. The same filter circuits that reject third-order harmonics also provide second-order harmonic rejection and improve overall frequency selectivity. This merging of functions reduces the total number of discrete filter components needed compared to implementing separate filters for each harmonic order.
Solution Approach 2:
The LC filter circuits are designed with universal applicability, serving multiple functions simultaneously: they act as harmonic rejection filters, impedance matching networks, and frequency selective elements. This multi-functionality allows a single filter circuit to address multiple performance issues, reducing the overall component count and circuit area.
3Reliability
If complex filtering mechanisms are used to reject harmonic conversion gain, then harmonic suppression improves, but power consumption increases
Solution Approach 1:
The patent employs passive LC filter circuits that consume no active power during operation. Rather than using active filtering mechanisms that require power-hungry operational amplifiers or digital signal processing, the solution uses passive inductors and capacitors that provide harmonic rejection through their inherent frequency-selective properties without consuming power.
Solution Approach 2:
The LC filter circuits are designed to be self-regulating, using the natural resonant properties of inductors and capacitors to automatically reject harmonic frequencies. The filters do not require external control signals or active power management, as they inherently perform the filtering function based on the frequency characteristics of the signals passing through them.
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
Effectively suppresses harmonic conversion gain, improving mixer performance by minimizing undesired in-band spurs while maintaining efficiency and reducing component complexity and power usage.
Implementation Method 1
a harmonic conversion gain rejection filter coupled between a source terminal of the first mixer transistor and a source terminal of the second mixer transistor... The harmonic conversion gain rejection filter can include an inductor coupled between the source terminal of the first mixer transistor and the source terminal of the second mixer transistor, and an adjustable capacitor coupled between the source terminal of the first mixer transistor and the source terminal of the second mixer transistor
Implementation Method 2
an output transformer having a primary coil coupled between the first pair of mixer transistors and between the second pair of mixer transistors and having a secondary coil
Implementation Method 3
an output filter circuit interposed between the primary coil and the secondary coil of the output transformer. The output filter can include a filter coil and a filter capacitor coupled in parallel with the filter coil
Data Source
AI summary
Mixer circuitry can include a first mixer transistor configured to receive a first oscillating signal, a second mixer transistor configured to receive a second oscillating signal, and a harmonic conversion gain rejection filter coupled between a source terminal of the first mixer transistor and a source terminal of the second mixer transistor. The harmonic conversion gain rejection filter can be configured to reject a harmonic conversion gain of the mixer circuitry. The mixer circuitry can further include a third mixer transistor configured to receive the first oscillating signal, a fourth mixer transistor configured to receive the second oscillating signal, and another harmonic conversion gain rejection filter coupled between a source terminal of the third mixer transistor and a source terminal of the fourth mixer transistor. The mixer circuitry can further include an output transformer and a notch filter interposed between coils of the output transformer.