RF Switch Amplitude-Phase Cancelling Block Third Harmonic Suppression
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Solution Overview
Problem
Radio-frequency (RF) switches in wireless devices generate harmonics, particularly third harmonics, which are difficult to manage without increasing FET size, slowing switching speed, or adding signal loss with filters.
Innovation Solution
The implementation of an amplitude-phase cancelling block across switch arms in RF switch circuits, using anti-parallel diodes and capacitances in a voltage divider configuration, to cancel third harmonics by phase shifting and amplitude matching between ON and OFF states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If FET size is increased to reduce third harmonics, then harmonic suppression is improved, but switching speed decreases
Solution Approach 1:
The invention converts the harmful third harmonics generated by the switch into useful cancellation signals. By intentionally generating third harmonics in the cancelling block with opposite phase, the harmful emissions are transformed into a beneficial cancellation mechanism that suppresses the original harmonics without requiring larger FETs.
Solution Approach 2:
The amplitude-phase cancelling block serves as an intermediary element between the switch and the output. This blocking circuit generates counter-phase third harmonics that mediate the cancellation process, allowing harmonic suppression without directly modifying the switch FET dimensions or switching characteristics.
2Object-generated harmful factors
If filters are added to suppress third harmonics, then harmonic suppression is improved, but signal loss increases
Solution Approach 1:
Instead of using passive filters that dissipate harmonic energy as loss, the invention converts the harmonic suppression problem into an active cancellation process. The harmful third harmonics are transformed into useful cancellation signals through the amplitude-phase cancelling block, achieving suppression without the energy loss inherent in traditional filtering approaches.
3Object-generated harmful factors
If FET size is increased to reduce third harmonics, then harmonic suppression is improved, but device area increases
Solution Approach 1:
The invention segments the harmonic suppression function from the main switch FETs. Instead of enlarging the switch FETs to handle harmonic suppression, the function is separated into a dedicated amplitude-phase cancelling block that generates counter-phase harmonics. This segmentation allows the main switch to remain compact while the cancellation block handles the harmonic suppression task.
4Object-generated harmful factors
If switching speed is reduced to suppress third harmonics, then harmonic suppression is improved, but productivity decreases
Solution Approach 1:
The invention converts the switching operation itself, which generates harmful third harmonics, into a beneficial source of cancellation signals. The third harmonics generated during normal switching operations are captured and reprocessed by the amplitude-phase cancelling block to create counter-phase cancellation signals, maintaining high switching speeds while achieving harmonic suppression.
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
Significantly reduces third harmonic amplitude and maintains low insertion loss, meeting performance requirements like 3fo harmonics below −105 dB at cellular band B17 without slowing switching speed or adding signal loss.
Implementation Method 1
The diodes of the first and second combinations can be configured to generate harmonics by voltage distributed by a voltage divider formed by the resistances of the first and second combinations.
Implementation Method 2
The capacitances of the first and second combinations can be configured to provide respective phase shifts of the harmonics.
Implementation Method 3
The anti-parallel configuration of the diodes of the first and second combinations can result in the amplitude-phase cancelling block generating substantially nil amount of a second harmonic.
Implementation Method 4
configured such that a third harmonic resulting from an ON state of the first switch arm is substantially canceled by a third harmonic resulting from an OFF state of the second switch arm
Data Source
AI summary
Radio-frequency switch having improved linearity. In some embodiments, a radio-frequency switch circuit can include first and second switch arms, with each switch arm including a plurality of transistors arranged in series to form a stack between a first node and a second node. The first node of the first switch arm can be coupled to the first node of the second switch arm. The radio-frequency switch circuit can further include an amplitude-phase cancelling block implemented across one or more transistors of each switch arm, and configured such that a third harmonic resulting from an ON state of the first switch arm is substantially canceled by a third harmonic resulting from an OFF state of the second switch arm.