TDD Radio Transmitter Reflection Cancellation for PA Isolation
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Solution Overview
Problem
In time division duplex (TDD) systems, the isolation performance of the power amplifier (PA) backend is poor due to reflections from the high-power switch and circulator, which interfere with the digital pre-distortion (DPD) process, leading to inaccurate model construction and deteriorated linearization performance.
Innovation Solution
A radio transmitter design incorporating a reflection cancellation unit, such as an impedance tuner, is introduced between the switch and termination load to generate a controlled reflection signal that offsets the sum of reflection signals at the circulator port, improving isolation by canceling out unwanted reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a traditional PA backend is used in TDD systems, then the structure is simple, but the isolation performance is poor due to reflections from the high-power switch and circulator
Solution Approach 1:
An impedance tuner is introduced as an intermediary component between the high-power switch and the circulator. The impedance tuner actively manages signal reflections by adjusting impedance matching, thereby improving isolation performance without fundamentally changing the overall TDD system structure.
Solution Approach 2:
The impedance tuner dynamically adjusts impedance parameters to optimize signal transmission and minimize reflections. By changing impedance parameters in real-time, the system achieves better isolation performance while maintaining structural simplicity.
2Reliability
If digital pre-distortion is implemented, then linearization performance is improved, but the accuracy deteriorates when feedback signal is interfered with by reflections
Solution Approach 1:
The impedance tuner performs preliminary anti-action by preemptively canceling out reflections before they can interfere with the feedback signal. This preliminary intervention ensures that the feedback signal remains clean and accurate for DPD model construction, thereby maintaining both linearization performance and measurement precision.
Solution Approach 2:
The system uses feedback from the PA output to monitor reflections and adjust the impedance tuner accordingly. This feedback mechanism ensures that the impedance tuning is continuously optimized to protect the feedback signal quality, thereby maintaining DPD accuracy while achieving good linearization performance.
3Use of energy by moving object
If the PA works closely to saturation for better efficiency, then power consumption is reduced, but linearity deteriorates requiring linearization techniques
Solution Approach 1:
The impedance tuner performs preliminary action by pre-adjusting the impedance matching before the distorted signal reaches the feedback path. This preliminary correction helps maintain signal integrity and reduces the burden on DPD, allowing the PA to operate more efficiently while maintaining acceptable linearity.
Solution Approach 2:
The system converts the harmful effect of PA saturation (increased efficiency but worse linearity) into a benefit by using the impedance tuner to manage the resulting reflections. The reflections that would normally degrade performance are instead managed constructively, allowing the PA to operate at higher efficiency points while maintaining linearity through coordinated impedance tuning and DPD.
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
The proposed design significantly enhances the isolation performance of the PA backend in TDD systems, improving system linearity and reducing interference, thereby enhancing the effectiveness of digital pre-distortion.
Implementation Method 1
A radio transmitter design incorporating a reflection cancellation unit, such as an impedance tuner, is introduced between the switch and termination load to generate a controlled reflection signal that offsets the sum of reflection signals at the circulator port
Data Source
AI summary
A radio transmitter as well as a method and a controller therefor are disclosed. According to an embodiment, the radio transmitter comprises a power amplifier, a filter unit, a circulator, a switch and a reflection cancellation unit. The filter unit is capable of filtering an output from the power amplifier during a downlink time division duplex (TDD) slot and filtering an uplink signal during an uplink TDD slot. The circulator has a first port coupled to the power amplifier, a second port coupled to the filter unit, and a third port coupled to the switch. The switch is capable of coupling the third port of the circulator to a termination load during the downlink TDD slot and coupling the third port of the circulator to an uplink reception path during the uplink TDD slot. The reflection cancellation unit is coupled between the switch and the termination load and is capable of generating a first reflection signal that propagates to the first port of the circulator via the switch and the third port of the circulator during the downlink TDD slot.