Double-Balanced Mixer Input Shorting for Harmonic Suppression
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Solution Overview
Problem
Double-balanced mixers in modulators experience non-linearity due to non-instantaneous switching transitions, leading to harmonic creation and interference in neighboring channels, especially in high-power output applications where large signal currents cannot be switched instantly.
Innovation Solution
Implementing a shorting mechanism during transition times by adding a switch transistor controlled by a control and clock generation circuit to blank the mixer core output, eliminating harmonics and improving linearity, with a trade-off in signal gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the dimensions of switching transistors are increased to handle larger signal currents, then the current handling capability is improved, but the transition time increases and nonlinearity worsens
Solution Approach 1:
The patent applies preliminary action by pre-charging the storage nodes to the input voltage level before the switching event. This preparatory action ensures that when the switching transistor turns on, there is no voltage difference to drive current flow during the transition, thereby eliminating the non-linear charging effect and harmonics while allowing larger signal currents to be handled without increasing transition time
2Manufacturing precision
If the transition time of switching transistors is reduced for better linearity, then mixer linearity is improved, but the maximum signal current that can be processed is reduced
Solution Approach 1:
The patent uses preliminary action by pre-charging storage nodes to the input voltage level before switching occurs. This eliminates voltage differences during the transition period, allowing switching transistors to handle larger currents without increasing transition time or generating harmonics, thus simultaneously improving both linearity and current handling capability
Solution Approach 2:
The patent introduces storage nodes as intermediary elements between the input signal and the switching transistors. These storage nodes act as mediators that temporarily hold the pre-charged voltage, isolating the switching transistor from voltage transients during switching and enabling it to operate linearly even with large signal currents
Data Source
AI summary
A double-balanced mixer is provided having a shorting switch connecting the signal inputs to the mixer core. A timer circuit provides pulses to close the switch, thereby shorting those inputs at times when the switches of the mixer core are switching. This is done because non-linear components in the output are produced at those times and therefore they can be removed if the signal input is shorted at those times.