Integrated TDD Isolator Circuit for Low-Loss High-Linearity Switching
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Solution Overview
Problem
Current Time-Division Duplex (TDD) transceivers face challenges in achieving low insertion loss and high linearity due to the use of CMOS switches, which result in increased non-linearity and reduced Adjacent Channel Leakage Power Ratio (ACLR), and require external components, leading to high costs and complex biasing control.
Innovation Solution
An integrated isolator circuit with a third-order filter configuration, utilizing a capacitor and inductor network with a switch-controlled impedance, operates as a peak and notch resonance filter to provide high impedance during Tx mode and low impedance during Rx mode, reducing voltage swing and enhancing linearity, and is tunable for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If CMOS switches are used to provide isolation in integrated Tx/Rx circuits, then device integration is improved, but linearity deteriorates due to high non-linearity with large signal voltage swings
Solution Approach 1:
The patent employs dynamic switching of capacitor connections to achieve different impedance states. During transmit mode, capacitors are connected to ground to present high impedance and isolate the receiver. During receive mode, capacitors are disconnected to present low impedance and minimize insertion loss. This dynamic reconfiguration allows the integrated isolator to maintain high linearity while adapting to different operating conditions.
Solution Approach 2:
The patent changes the impedance parameter of the isolator circuit by switching capacitor connections between ground and floating states. This parameter change enables the circuit to transition between high-impedance (isolation) and low-impedance (low insertion loss) states, resolving the contradiction between integration benefits and linearity requirements.
2Strength
If multiple switches are stacked to handle high Tx signal swing, then protection from breakdown is improved, but insertion loss increases during Rx operation
Solution Approach 1:
The patent uses a single switch rather than multiple stacked switches, applying partial action by connecting capacitors to ground only when needed for isolation. This approach provides sufficient voltage handling capability during transmit mode while minimizing insertion loss during receive mode, avoiding the excessive loss that would result from multiple stacked switches.
Solution Approach 2:
The patent creates an equivalent isolation effect using capacitor-switch combinations that replicate the function of multiple stacked switches but with lower insertion loss. The capacitors provide the necessary impedance transformation to achieve isolation without requiring multiple physical switch stacks.
3Reliability
If external components are used to implement TRX isolators, then isolation performance is improved, but cost and board area increase
Solution Approach 1:
The patent merges the isolator function with the existing transceiver circuitry by integrating capacitor-switch combinations directly into the Tx/Rx path. This consolidation provides the necessary isolation performance while reducing the number of external components, lowering cost and board area compared to traditional external isolator implementations.
Solution Approach 2:
The integrated capacitor-switch circuit serves multiple functions: it provides isolation during transmit mode, minimizes insertion loss during receive mode, and can be implemented using standard CMOS processes. This multi-functionality eliminates the need for separate external isolator components while maintaining performance requirements.
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 integrated isolator circuit achieves low Tx and Rx insertion losses, high linearity, and reduced size and cost, with improved ACLR, enabling efficient data transmission in TDD transceivers.
Implementation Method 1
An integrated isolator circuit with a third-order filter configuration, utilizing a capacitor and inductor network with a switch-controlled impedance, operates as a peak and notch resonance filter
Data Source
Figure 1~2
Figure 3(a)~3(c)
Figure 4(a)~4(b)
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.