IM2 Injection Circuit for RF Amplifier IMD3 Cancellation
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Solution Overview
Problem
Designing satisfactory amplifier circuitry for electronic devices with wireless communications capabilities is challenging due to non-linear characteristics of transistors, which generate third-order intermodulation distortion (IMD3) that degrade signal-to-noise and distortion ratio (SNDR) and error vector magnitude (EVM).
Innovation Solution
Implementing a second-order intermodulation (IM2) generation circuit coupled with capacitance neutralization transistors to produce IM2 signals that cancel out third-order non-linearity components, reducing amplitude modulation to amplitude modulation (AMAM) and amplitude modulation to phase modulation (AMPM) distortions while preserving enhanced reverse isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional amplifier circuitry is used, then the device can transmit and receive radio-frequency signals, but third-order intermodulation distortion degrades signal quality and reduces performance
Solution Approach 1:
The patent applies preliminary anti-action by generating second-order intermodulation signals in advance that will cancel the harmful third-order intermodulation distortion when they interact with the non-linear transistor characteristics. The IM2 generation circuit produces signals at frequencies that, when mixed with the fundamental signals through the transistor's non-linearity, create third-order components that are 180 degrees out of phase with the distortion products, thereby canceling them before they degrade the signal quality.
Solution Approach 2:
The patent converts the harmful non-linear characteristics of transistors into a beneficial effect. By intentionally exploiting the transistor's non-linearity to generate and mix second-order intermodulation signals, the circuit transforms what would normally be distortion into a mechanism for canceling third-order intermodulation distortion. The non-linearity that causes harm is repurposed to create cancellation signals that improve overall signal quality.
2Power
If amplifier gain is increased to improve signal strength, then transmission distance is extended, but non-linear distortion increases and degrades signal-to-noise ratio
Solution Approach 1:
The patent converts the harmful non-linear distortion that increases with amplifier gain into a beneficial cancellation mechanism. The IM2 generation circuit produces second-order intermodulation signals that, when amplified along with the fundamental signals, generate third-order components through the transistor's non-linearity that cancel the distortion products. This allows the amplifier to operate at higher gains while maintaining signal-to-noise ratio.
Solution Approach 2:
The patent changes the operating parameters of the amplifier by introducing additional signal components (second-order intermodulation signals) and adjusting the bias conditions of the transistors. The gate voltages are configured to optimize the third-order intercept point, and the IM2 generation circuit parameters are tuned to produce the appropriate cancellation signals, allowing the amplifier to maintain high gain with improved linearity.
Data Source
AI summary
An electronic device may include wireless circuitry. The wireless circuitry can include a first input transistor, a first capacitance neutralization having a source terminal coupled to a tail node, and a second order intermodulation generation circuit configured to produce second order intermodulation signals at the tail node. The wireless circuitry can further include a second input transistor and a second capacitance neutralization transistor having a source terminal coupled to the tail node. The first and second capacitance neutralization transistors can be cross-coupled with the input transistors. A fixed or adjustable current source can be coupled to the tail node. The second order intermodulation generation circuit can include a transistor biased in a weak inversion mode.