Doherty Amplifier TIP Circuit for Adjustable Alpha and PAE
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Solution Overview
Problem
Conventional Doherty amplifiers have a constant alpha factor, which is not beneficial across different modulation schemes, leading to poorer power added efficiency (PAE) at high peak-to-average power ratios, particularly in battery-powered RF transceivers.
Innovation Solution
A Doherty amplifier circuit with a tunable impedance and phase (TIP) circuit, allowing for adjustable alpha factor by replacing the conventional quarter wave transmission line impedance inverter, maintaining the phase of the carrier amplifier at 90° with minimal phase variation, and enabling adjustment of the impedance and phase shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a constant alpha factor is used in conventional Doherty amplifiers, then the circuit structure is simple, but power added efficiency deteriorates at high peak-to-average power ratios
Solution Approach 1:
The patent applies the dynamics principle by replacing the conventional fixed quarter-wave transmission line impedance inverter with a tunable impedance and phase (TIP) circuit. This TIP circuit dynamically adjusts the alpha factor based on the modulation scheme and operating conditions, transforming the static constant-alpha Doherty amplifier into a dynamic variable-alpha amplifier. The tunable components within the TIP circuit enable real-time optimization of the impedance transformation ratio, allowing the amplifier to adapt to different peak-to-average power ratios and maintain high power added efficiency across varying operating conditions.
Solution Approach 2:
The patent implements parameter changes by modifying the alpha factor from a fixed constant to a tunable parameter. The TIP circuit contains adjustable impedance elements that change the characteristic impedance of the impedance inverter, thereby altering the alpha factor (α = Z_L / Z_INV). This parameter adjustment enables optimization of power added efficiency for different modulation schemes (e.g., QPSK, 16-QAM, 64-QAM) and operating conditions, directly addressing the efficiency deterioration problem at high peak-to-average power ratios.
2Ease of manufacture
If a constant alpha factor is used, then the amplifier design is straightforward, but adaptability to different modulation schemes deteriorates
Solution Approach 1:
The patent applies dynamics by introducing a tunable impedance and phase circuit that can adapt its characteristics to match different modulation schemes. The TIP circuit's adjustable components allow the amplifier to dynamically reconfigure its impedance transformation properties, enabling optimal performance across various modulation types and peak-to-average power ratios without requiring multiple fixed designs.
Solution Approach 2:
The patent implements universality through the TIP circuit, which serves multiple functions: it acts as an impedance inverter, provides phase shifting, and enables alpha factor adjustment. This single multi-functional circuit replaces the conventional fixed quarter-wave transmission line, allowing the same amplifier architecture to efficiently support different modulation schemes (QPSK, 16-QAM, 64-QAM, etc.) and operating conditions, thereby enhancing adaptability while maintaining design coherence.
3Stability of the object's composition
If the quarter wave transmission line impedance inverter is used, then the phase shift is fixed at 90°, but the ability to optimize for different power levels is limited
Solution Approach 1:
The patent applies dynamics by replacing the fixed quarter-wave transmission line with a tunable impedance and phase circuit. While the conventional approach provides stable fixed 90° phase shift, the TIP circuit dynamically adjusts both impedance and phase characteristics. The circuit maintains approximately 90° phase shift through its tuning mechanism while simultaneously optimizing the alpha factor for different power levels and modulation schemes, achieving both stability and adaptability.
Solution Approach 2:
The patent implements parameter changes by modifying the characteristic impedance of the impedance inverter while maintaining the phase shift function. The TIP circuit contains tunable elements that allow adjustment of the impedance transformation ratio (alpha factor) independent of the phase shift requirement. This enables optimization of power added efficiency for different operating conditions while preserving the necessary 90° phase shift for proper Doherty amplifier operation.
Data Source
AI summary
A Doherty amplifier circuit having a tunable impedance and phase (“TIP”) circuit to provide an adjustable alpha factor, which allows for a selection of power added efficiency (PAE) curves that are useful for applications having different modulations or to meet other criteria. Embodiments include a Doherty amplifier having a TIP circuit that provides for tunability of the impedance ZINV (resulting in an adjustable alpha factor) while maintaining the phase of the output of the carrier amplifier at 90° (for a selected polarity)±a low phase variation. Embodiments of the TIP circuit include one or more series-connected TIP cells comprising at least one TIP circuit combined with a tunable phase adjustment circuit. In operation, when the impedance of a TIP cell is adjusted, adjustments within the cell are also made to provide a phase shift correction back towards 90° (at the selected polarity).