Mixer Circuitry Using Inverted LO Capacitors for Phase Noise Cancellation
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Solution Overview
Problem
Designing a satisfactory mixer for electronic devices with wireless communications capabilities is challenging due to noise figure degradation caused by phase noise associated with the local oscillator, which can couple to the input port through parasitics, degrading the noise performance of the mixer circuitry.
Innovation Solution
Incorporating an oscillator phase noise cancellation capacitor that receives inverted oscillator signals to offset parasitic coupling noise, improving noise figure performance by canceling phase noise associated with the local oscillator signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a mixer is designed with standard oscillator coupling, then the mixer can operate with simple circuitry, but phase noise from the oscillator couples to the input port through parasitics, degrading noise performance
Solution Approach 1:
An intermediary capacitor is introduced between the oscillator signal path and the mixer input port. This capacitor couples the oscillator signal to the mixer while providing a controlled impedance path that prevents phase noise from coupling through parasitic elements to the input port, thus mediating between the oscillator and mixer to eliminate the harmful noise coupling.
Solution Approach 2:
The harmful phase noise coupling path is extracted and separated from the main signal path. By using the intermediary capacitor to establish a dedicated coupling path, the phase noise component is effectively taken out from the input port, preventing it from degrading the noise figure while allowing the necessary oscillator signal to reach the mixer.
2Productivity
If the oscillator signal is directly coupled to the mixer, then the mixing operation is efficient, but phase noise associated with the oscillator degrades the noise performance of the mixer circuitry
Solution Approach 1:
The intermediary capacitor serves as a mediator that allows the oscillator signal to efficiently couple to the mixer for effective mixing operation, while simultaneously blocking the phase noise from reaching the input port. This mediator enables the mixing function to proceed efficiently without the harmful side effect of phase noise degradation.
3Ease of manufacture
If parasitic coupling paths are present in the mixer circuit, then the circuit can be implemented with standard layout, but these parasitics cause phase noise to couple to the input port, degrading performance
Solution Approach 1:
The intermediary capacitor is strategically placed in the circuit layout to provide a controlled coupling path that overrides the effect of parasitic elements. This allows the circuit to be implemented with standard layout practices while the capacitor mediates the signal transmission to prevent phase noise coupling, thus maintaining both ease of manufacture and noise performance.
Data Source
AI summary
An electronic device may include wireless circuitry with a baseband processor, a transceiver, a front-end module, and an antenna. The transceiver may include mixer circuitry. The mixer circuitry may include switches controlled by oscillator signals. The mixer circuitry may also include oscillator phase noise cancelling capacitors controlled by inverted oscillator signals. Operated in this way, the mixer circuitry exhibits improved noise figure performance.