Integrated TDD Isolator Circuit for Low-Loss High-Linearity Switching
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Solution Overview
Problem
Current integrated isolator circuits in wireless communication devices face challenges with high Tx insertion loss, high Rx insertion loss, and non-linearity due to the use of CMOS switches, which result in poor Adjacent Channel Leakage Power Ratio (ACLR) and increased costs and board area.
Innovation Solution
An integrated isolator circuit using a third-order filter configuration with a capacitor and inductor network, where the first switch controls impedance, reducing voltage swing on switches and achieving high linearity by presenting high impedance during Tx mode and low impedance during Rx mode, and allowing for tunability of peak and notch frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If CMOS switches are used to provide isolation in integrated isolator circuits, then integration and cost are improved, but linearity and ACLR deteriorate due to non-linear operation with large signal voltage swings
Solution Approach 1:
The voltage swing is segmented across multiple components: the first capacitor C1 handles a portion of the voltage swing, while the first switch T1 handles a reduced portion. This segmentation allows the switch to operate more linearly while maintaining the required isolation functionality.
Solution Approach 2:
The first capacitor C1 acts as an intermediary element between the antenna and the first switch T1. It shares the voltage swing burden, thereby protecting the switch from excessive voltage stress and improving its linearity of operation.
2Reliability
If multiple switches are stacked to handle high Tx signal voltage swing, then voltage breakdown is avoided, but insertion loss during Rx operation increases
Solution Approach 1:
The circuit uses a single switch T1 with controlled biasing rather than multiple stacked switches. The biasing parameters are optimized to allow the switch to handle high voltage swings during Tx mode while maintaining low insertion loss during Rx mode, achieving both voltage handling and low loss objectives.
3Reliability
If high impedance is presented during Tx mode for isolation, then Tx-Rx isolation is improved, but Tx insertion loss increases
Solution Approach 1:
The isolator circuit dynamically switches between Tx and Rx modes using the first switch T1. During Tx mode, the circuit presents high impedance at the operating frequency through the LC resonant network (C1-L1-C2) to achieve isolation, while during Rx mode it presents low impedance for minimal insertion loss. The dynamic switching allows both isolation and low loss requirements to be met at different times.
4Reliability
If external components are used for TRX isolator functionality, then performance is improved, but cost and board area increase
Solution Approach 1:
The patent merges the isolator functionality with integrated circuit components (CMOS switches and on-chip passive elements L1, C1, C2). By combining the switch T1 with the LC resonant network and integrating them on the same chip, the design achieves high performance isolation while minimizing board area and eliminating the need for external discrete components.
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 achieves low Tx and Rx insertion losses, improved linearity, and reduced costs and size, with potential for even better performance using MEMS technology, while maintaining high Tx-Rx isolation and minimizing switch non-linearity.
Implementation Method 1
The impedance of the integrated isolator circuit at the operating frequency is controlled by the first switch. The circuit comprises a first capacitor connected in series with a first switch, a first inductor connected between the first and second nodes, forming a resonant circuit that achieves high impedance at the operating frequency.
Implementation Method 2
The first switch has an on state and an off state, and the integrated isolator circuit is configured to have a different impedance at a certain operating frequency by controlling the state of the first switch.
Data Source
AI summary
An integrated isolator circuit for isolating receiver and transmitter in a Time-Division Duplex transceiver is disclosed. The integrated isolator circuit comprises a first node, a second node and a third node. The integrated isolator circuit further comprises a fist capacitor connected in series with a first switch and connected between the first and second nodes. The integrated isolator circuit further comprises a first inductor connected between the first and second nodes and a second capacitor connected between the second node and the third node. The first switch has an on state and an off state, and the integrated isolator circuit is configured to have a different impedance at a certain operating frequency by controlling the state of the first switch.