Differential Amplifier Harmonic Termination With Resonant LC Tanks
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Solution Overview
Problem
RF circuitry in wireless communications devices experiences harmonic distortions, particularly second and third harmonics, which affect performance metrics such as ACLR and EVM, despite advancements in RF circuitry.
Innovation Solution
A resonant circuit comprising specific capacitors and inductors is coupled between the output terminals of a differential amplifier to control harmonic termination, including suppression of second and third harmonics, enhancing impedance control at these frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resonant circuit is added to control harmonic termination, then harmonic distortion is reduced and amplifier performance is improved, but device complexity increases
Solution Approach 1:
The resonant circuit is segmented into multiple independent LC tanks, each targeting specific harmonic frequencies (second harmonic and third harmonic). This segmentation allows selective suppression of different harmonics using separate capacitor-inductor pairs (C1-L1 for second harmonic, C2-L2 for third harmonic), enabling precise control without requiring a monolithic complex circuit.
Solution Approach 2:
The resonant circuit acts as an intermediary element coupled between the amplifier output terminals. This intermediary structure provides harmonic termination by presenting specific impedance at harmonic frequencies, mediating between the amplifier and the load to suppress harmonics while maintaining fundamental signal integrity.
2Measurement precision
If harmonic suppression is enhanced, then ACLR and EVM are improved, but power-added efficiency decreases
Solution Approach 1:
The resonant circuit parameters (capacitance values C1, C2 and inductance values L1, L2) are specifically tuned to resonate at harmonic frequencies (2ω and 3ω). By adjusting these parameters, the circuit presents high impedance at harmonic frequencies to suppress them, while maintaining appropriate impedance matching at the fundamental frequency to preserve power efficiency.
Solution Approach 2:
The resonant circuit utilizes electrical resonance phenomena where LC tanks oscillate at specific frequencies (second and third harmonics). This resonance creates high impedance at these frequencies, effectively suppressing harmonic content through vibrational energy storage and release in the reactive components, thereby improving spectral efficiency without excessive power loss.
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 solution improves amplifier performance by reducing ACLR, EVM, and increasing power-added efficiency (PAE) by effectively suppressing harmonics in the amplifier output.
Implementation Method 1
A resonant circuit comprising specific capacitors and inductors is coupled between the output terminals of a differential amplifier to control harmonic termination
Data Source
AI summary
Certain aspects of the present disclosure provide techniques for harmonic termination for a differential amplifier. An example apparatus comprises an amplifier configured to output a differential signal via a first output terminal and a second output terminal. The apparatus includes a resonant circuit coupled between the first output terminal and the second output terminal of the amplifier. The resonant circuit comprises a first capacitor, a second capacitor, a third capacitor, a first inductor, and a second inductor. The third capacitor is coupled between separate terminals of the inductors.