Digital Envelope Tracker Timing for Low-Peaking Supply Filters
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Solution Overview
Problem
Existing digital envelope trackers for RF power amplifiers face a contradiction between achieving low loss and minimizing peaking in the supply filter's step response, as lossless LC filters tend to peak and ring, violating the maximum voltage requirement.
Innovation Solution
Incorporating a snubber network with a capacitor and resistor to dissipate ringing energy reduces peaking, but increases AC losses. Instead, a low-loss and high-Q supply filter is designed with a level selection circuitry and secondary switching events to generate a filter response with smaller peaking, eliminating the need for a snubber resistor and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a lossless LC filter is used in the supply filter, then the efficiency of the overall envelope tracking is improved, but the filter peaks and rings which violates the maximum voltage requirement of the power amplifier
Solution Approach 1:
A snubber network is introduced as an intermediary component between the LC filter and the power amplifier. This snubber network acts as a mediator that absorbs the ringing energy from the lossless LC filter, preventing voltage peaks from violating the maximum voltage requirement while allowing the LC filter to maintain its low-loss characteristic.
Solution Approach 2:
The ringing energy that would normally be harmful and cause voltage peaks is converted into a beneficial effect by using the snubber network to dissipate it in a controlled manner. The harmful ringing is transformed into a manageable transient response that settles within voltage limits, turning a potential failure mode into a design feature.
2Reliability
If a snubber network is added to reduce peaking, then the voltage requirement compliance is improved, but the AC losses in the supply filter increase
Solution Approach 1:
The operating parameters of the snubber network are optimized to minimize AC losses. By carefully selecting the snubber resistor value and timing characteristics, the network dissipates only the necessary ringing energy while maintaining low overall AC losses in the supply filter.
Solution Approach 2:
The snubber network operates periodically during switching transitions, activating only when needed to dampen ringing. This periodic operation minimizes energy loss by keeping the snubber inactive during normal operation and only engaging during transient events that require damping.
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
This approach achieves low peaking at the supply filter's output without a snubber resistor, enhancing the efficiency of digital envelope tracking and allowing for a simpler supply filter topology, thereby reducing power consumption and maintaining efficiency.
Implementation Method 1
Incorporating a snubber network with a capacitor and resistor to dissipate ringing energy reduces peaking
Implementation Method 2
A supply filter (e.g. a passive filter) between the switch and the PA power amplifier input is used to smoothen the transition from one voltage level to another
Implementation Method 3
a lossless LC filter does peak and ring
Data Source
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AI summary
A digital envelop tracker for a power amplifier. The digital envelop tracker includes a supply filter for filtering a supply voltage to a power amplifier, a level selection circuitry configured to determine a level of supply voltage based on an instantaneous power of an input data stream, schedule a series of switching events based on the determined level of supply voltage, and generate a level select signal based on the scheduled series of switching events, and a switch for connecting one of supply voltages to the supply filter based on the level select signal. The level selection circuitry schedules a primary switching event of the switch based on the determined level of supply voltage and secondary switching events of the switch delayed with respect to the primary switching event based on the determined level of supply voltage to generate a filter response of the supply filter with smaller peaking.