RF Amplifier Common-Mode Impedance Tuning for Modulation-Specific EVM
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Solution Overview
Problem
Designing a satisfactory power amplifier for electronic devices with wireless communications capabilities is challenging due to the need for different amplitude modulation to amplitude modulation (AMAM) and amplitude modulation to phase modulation (AMPM) responses depending on the wireless modulation scheme, which affects error vector magnitude (EVM) and overall performance.
Innovation Solution
Incorporating a common mode impedance tuning circuit with a switch and capacitors between the output nodes of the radio-frequency amplifier, allowing selective activation or deactivation based on the wireless modulation scheme to achieve the desired AMAM/AMPM response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed common mode impedance is used in the radio-frequency amplifier, then the circuit design is simplified, but the amplifier cannot achieve optimal AMAM/AMPM response for different wireless modulation schemes
Solution Approach 1:
The patent implements dynamic common mode impedance tuning by introducing a switchable capacitor connected between the tail node and ground through a control switch. The capacitor can be selectively activated or deactivated based on the detected modulation scheme, dynamically adjusting the common mode impedance to optimize AMAM/AMPM response for different wireless standards (e.g., Wi-Fi, Bluetooth, cellular)
Solution Approach 2:
The patent changes the electrical parameter (common mode impedance) of the amplifier circuit by adding a switchable capacitor that modifies the tail node impedance. A control circuit detects the active modulation scheme and adjusts the capacitor's inclusion in the circuit, thereby changing the common mode impedance parameter to match the requirements of different wireless communication protocols
2Reliability
If different common mode impedances are provided for different modulation schemes, then the AMAM/AMPM response is optimized, but the circuit complexity increases due to additional tuning components and control logic
Solution Approach 1:
The patent applies local quality by making only the necessary local modification to the amplifier circuit - adding a single switchable capacitor at the tail node rather than redesigning the entire amplifier. This localized approach optimizes the common mode impedance specifically where needed while keeping the rest of the circuit unchanged, thus improving EVM performance with minimal added complexity
Solution Approach 2:
The patent implements feedback by using a control circuit that detects which modulation scheme is currently active and uses this information to control the switch state of the capacitor. This closed-loop feedback mechanism ensures the common mode impedance is automatically adjusted to the optimal value for the current wireless standard, improving reliability without requiring manual intervention
Data Source
AI summary
Wireless circuitry is provided that includes an antenna and a radio-frequency amplifier coupled to the antenna. The radio-frequency amplifier can include a first input transistor having a drain terminal coupled to a first node, a second input transistor having a drain terminal coupled to a second node, and a common mode impedance tuning circuit coupled between the first and second nodes. The common mode impedance tuning circuit can be configured to tune a common mode impedance at the first and second nodes of the radio-frequency amplifier. The common mode impedance tuning circuit can be configured to provide a first common mode impedance when the amplifier is operating in accordance with a first set of operating conditions and can be configured to provide a second common mode impedance, different than the first common mode impedance, when the amplifier is operating in accordance with a second set of operating conditions.