Envelope Tracking Bias Circuit With DC Offset Cancellation
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Solution Overview
Problem
Conventional envelope tracking bias circuits fail to match the envelope signal with the characteristics of power amplifiers, resulting in suboptimal performance due to the lack of consideration for PA characteristics.
Innovation Solution
An envelope tracking bias circuit comprising an envelope detection circuit, an envelope amplifier circuit with differential amplification and DC offset cancellation, and an envelope output circuit that selects either a negative or positive signal to generate an ET bias current, controlled by characteristic parameters of the power amplifier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional envelope tracking bias circuits provide the envelope signal without considering PA characteristics, then the circuit structure is simple, but the performance does not match PA characteristics
Solution Approach 1:
The bias circuit dynamically adjusts the envelope signal based on PA characteristics by selecting between different signal paths (positive or negative amplified signals) using control signals. The circuit transitions from a static conventional design to a dynamic adaptive system that responds to PA operating conditions, enabling the envelope signal to match PA characteristics while maintaining manageable complexity through controlled signal routing.
Solution Approach 2:
The circuit changes the parameter of the envelope signal by selectively applying either the positive or negative amplified signal based on control signals that reflect PA characteristics. This parameter change enables the bias to adapt to different PA operating modes and characteristics, resolving the contradiction between simplicity and adaptability.
2Reliability
If DC offset is not canceled in the envelope signal, then the circuit is simpler, but the linearity and efficiency of PA deteriorate
Solution Approach 1:
The DC offset is extracted and removed from the envelope signal through a dedicated DC offset cancellation path. The circuit separates the DC component from the AC envelope signal and cancels it appropriately, ensuring that only the useful envelope information is applied to the PA bias. This extraction approach improves PA linearity and efficiency while adding only the necessary minimal complexity for DC removal.
Solution Approach 2:
The DC offset, which is normally a harmful distortion component, is converted into a useful control element. The circuit deliberately generates and applies a canceling DC signal that is equal in magnitude but opposite in polarity to the unwanted DC offset, thereby eliminating its harmful effect. This transforms the DC offset problem into a solution mechanism that improves overall signal quality and PA performance.
3Measurement precision
If envelope signal is not differentially amplified, then the circuit complexity is reduced, but the signal quality and noise performance deteriorate
Solution Approach 1:
The envelope signal processing is segmented into distinct functional blocks: envelope detection, differential amplification with DC offset cancellation, and final bias generation. Each segment performs a specific function, allowing the differential amplification to be applied only where needed for signal quality improvement while keeping other parts of the circuit relatively simple. This segmentation enables better noise performance and signal quality without unnecessarily increasing overall circuit complexity.
Data Source
AI summary
An envelope tracking (ET) bias circuit includes an envelope tracking (ET) bias circuit includes an envelope detection circuit, an envelope amplifier circuit, and an envelope output circuit. The envelope detection circuit is configured to detect an envelope of an input signal, and output an envelope signal based on the detected envelope of the input signal. The envelope amplifier circuit is configured to differentially amplify the envelope signal in response to a first control signal and cancel a direct current (DC) offset of the envelope signal to output an amplified signal from which the DC offset is canceled. The envelope output circuit is configured to generate an ET bias current by selecting either one of a negative signal of the amplified signal and a positive signal of the amplified signal in response to a second control signal.