Zero-Peaking Envelope Tracking Modulator for Wideband PA Supply
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Solution Overview
Problem
Traditional fixed supply voltage in power amplifiers for wireless communication devices results in significant power loss as heat due to inefficiency, and wide-bandwidth envelope tracking designs are power-hungry, consuming additional quiescent current.
Innovation Solution
An envelope tracking supply modulator with a zero peaking circuit that adjusts the dominant pole frequency and gain to increase bandwidth without additional current consumption, using a multi-stage amplifier with adjustable zero peaking and continuous-time adaptive gain equalization for calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the transconductance (bias current) of a linear amplifier is increased to enhance bandwidth and linearity, then the bandwidth is improved, but the power consumption increases significantly
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the bias current of the linear amplifier based on the envelope signal characteristics. Instead of using a fixed high bias current, the system varies the current parameter according to the modulation depth and frequency requirements, achieving wide bandwidth while minimizing average power consumption. The bias current is modulated in conjunction with the envelope tracking signal to maintain amplifier linearity only when necessary.
Solution Approach 2:
The invention implements dynamic operation by making the bias current variable rather than static. The linear amplifier's transconductance parameter is dynamically controlled to match the instantaneous bandwidth requirements of the envelope tracking signal. This dynamic adjustment allows the system to achieve wide bandwidth performance only when needed, rather than maintaining high bandwidth capability continuously, thereby reducing overall power consumption.
2Speed
If a wide bandwidth linear amplifier is designed with high bias current, then the envelope tracking bandwidth is improved, but the quiescent current increases dramatically
Solution Approach 1:
The patent changes the bias current parameter from a fixed high value to a dynamically variable parameter. The bias current is adjusted according to the envelope signal's instantaneous frequency and amplitude requirements, ensuring that the linear amplifier operates with sufficient current only when wide bandwidth is needed, while reducing current during low-bandwidth periods to minimize quiescent power consumption.
Solution Approach 2:
The system employs feedback mechanisms to monitor the envelope tracking performance and adjust the bias current accordingly. By continuously measuring the actual bandwidth performance and comparing it with the desired performance, the feedback control system optimizes the bias current setting to achieve the minimum necessary current for the required bandwidth, thereby reducing quiescent current consumption.
3Device complexity
If the PA is biased with a fixed supply voltage, then the design is simple, but significant power loss occurs as heat
Solution Approach 1:
The invention transitions from a static fixed supply voltage design to a dynamic envelope-tracking supply voltage design. The PA supply voltage is modulated to follow the envelope of the RF input signal, allowing the amplifier to operate closer to its optimal efficiency point across varying signal conditions. This dynamic voltage adjustment reduces the voltage differential across the PA during low-power conditions, minimizing power dissipation as heat while maintaining signal fidelity.
Solution Approach 2:
The supply voltage parameter is changed from a fixed constant to a dynamically varying parameter that tracks the signal envelope. By adjusting the supply voltage parameter in real-time according to the instantaneous signal power requirements, the system achieves significant reductions in average power consumption and heat generation while maintaining the simplicity of the overall design through the use of envelope detection and modulation techniques.
Data Source
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AI summary
An envelope tracking supply modulator includes an amplifier circuit and a zero peaking circuit. The amplifier circuit receives an envelope input, generates a modulated supply voltage according to the envelope input, and provides the modulated supply voltage to a power amplifier. The zero peaking circuit is coupled to the amplifier circuit, and applies zero peaking to the amplifier circuit, where the zero peaking inserts a zero at a frequency.