Balun Circuit Using CPW and CPS Lines for Phase Difference
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Solution Overview
Problem
Existing balun circuits in microwave ICs face challenges in incorporating a 180-degree phase difference due to large circuit footprints required by rat race circuits, and previous balun designs result in unequal potentials for grounded conductors, leading to suboptimal performance in single-balanced mixer circuits.
Innovation Solution
A balun circuit design that connects the grounded conductors of CPW lines to achieve equal potentials, allowing for a compact footprint and ensuring equal electric power splitting, using CPW and CPS lines with specific length adjustments to maintain a 180-degree phase difference between output signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a rat race circuit is used to split high-frequency signals and impart a 180-degree phase difference, then the phase difference is achieved, but the circuit footprint becomes too large to incorporate in a microwave IC
Solution Approach 1:
The patent changes the fundamental parameter of phase difference generation from path length difference (rat race circuit) to potential difference (balun circuit). By connecting grounded conductors to equalize potentials and using CPW-to-CPS conversion, the circuit achieves 180-degree phase difference without requiring long transmission lines, thus reducing circuit footprint while maintaining phase accuracy.
2Area of stationary object
If a balun circuit is used to convert transmission lines and provide phase difference, then the circuit footprint is reduced, but the grounded conductors have unequal potentials leading to suboptimal performance
Solution Approach 1:
The patent explicitly applies the equipotentiality principle by adding connection sections that connect the grounded conductors of the CPW lines. This equalizes the potentials of the grounded conductors, ensuring that the balun circuit operates with proper symmetry and achieves optimal performance in single-balanced mixer circuits, while maintaining the compact footprint advantage.
3Area of stationary object
If CPW lines are converted to CPS lines without connecting grounded conductors, then the circuit remains compact, but the LO signals are not properly cancelled
Solution Approach 1:
By connecting the grounded conductors through connection sections, the patent ensures that both paths from the input to the output ports have equal potential references. This symmetry is crucial for proper LO signal cancellation in the 180-degree phase combination circuit, as it ensures that the in-phase LO signals undergo proper opposite-phase combination and are cancelled, preventing LO signal leakage.
Data Source
AI summary
A balun circuit includes a first CPW line 11, a second CPW line 12a, and a third CPW line 12b that serve as signal input/output ports; a first CPS line 14a that is a differential transmission line, the first CPS line 14a relaying the first CPW line 11 to the second CPW line 12a; a second CPS line 14b that is a differential transmission line, the second CPS line 14b relaying the first CPW line 11 to the third CPW line 12b; and at least one connection section that connects grounded conductors of each of the first CPW line 11, the second CPW line 12a, and the third CPW line 12b.