Vector Synthesizer Harmonics Cancellation Circuit for Better Linearity
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Solution Overview
Problem
Conventional vector synthesizers suffer from harmonic generation due to the nonlinearity of field effect transistors, leading to reduced gain and increased circuit nonlinearity, particularly from harmonic components leaked by the local oscillator in mixer operations.
Innovation Solution
A harmonics cancellation circuit is introduced, comprising capacitors connected to the source nodes of amplifiers receiving quadrature phase signals, with their other ends connected to a virtual ground, to cancel out harmonic components and improve linearity and power gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional field effect transistors are used in vector synthesizer, then device complexity is reduced, but harmonics are generated leading to reduced gain and increased circuit nonlinearity
Solution Approach 1:
The vector synthesizer is divided into multiple parallel amplifier channels (I+, I-, Q+, Q-), each processing specific quadrature phase signals. This segmentation allows independent optimization of each channel while collectively achieving harmonics cancellation through their combined output, resolving the contradiction between simple device structure and high linearity performance.
Solution Approach 2:
The patent employs asymmetric capacitor connections where capacitors are selectively connected to source nodes of specific amplifiers (I+ and Q- amplifiers) rather than all amplifiers uniformly. This asymmetric configuration creates destructive interference for harmonic components while preserving fundamental signal integrity, thereby improving linearity without requiring complete structural symmetry.
2Reliability
If harmonics cancellation circuit is added to vector synthesizer, then linearity and power gain are improved, but device complexity increases
Solution Approach 1:
Capacitors are introduced as intermediary elements connected between source nodes of amplifiers and ground. These capacitors act as frequency-selective pathways that allow fundamental signals to pass while blocking or redirecting harmonic frequencies, thereby improving linearity without requiring complex active cancellation circuits or additional amplifying stages.
Solution Approach 2:
The patent changes the electrical parameters (capacitance values) connected to different amplifier source nodes to achieve frequency-dependent impedance matching. By carefully selecting capacitor values, the circuit presents low impedance paths for harmonic frequencies to ground while maintaining high impedance for fundamental frequencies, thus improving linearity through parameter optimization rather than structural complexity.
Data Source
AI summary
The present disclosure relates to a harmonics cancellation circuit and a vector synthesis device using a harmonics cancellation circuit. A harmonics cancellation circuit according to an embodiment of the present disclosure includes a plurality of capacitors that one end is connected to a source node of a plurality of amplifiers receiving a plurality of quadrature phase signals, respectively; and a virtual ground to which the other end of each of the plurality of capacitors is commonly connected, wherein the source node of the plurality of amplifiers may be connected to a plurality of current controllers, respectively.