Phased Array Transmitter Auxiliary Vector Modulator AM to PM Distortion
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Solution Overview
Problem
Existing millimeter-wave power amplifiers face challenges in achieving high linearity and superior noise performance due to AM to PM distortion, which limits error vector magnitude (EVM) at both maximum and minimum power levels, and there is a lack of a robust phase-invariant gain control solution.
Innovation Solution
A phased array transmitter with an auxiliary vector modulator that adjusts output responsive to an input signal level, compensating for AM to PM distortion by using adaptive biasing to control the amplitude of in-phase and quadrature signals, thereby maintaining phase invariance and minimizing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a varactor is added at the input of the power amplifier to compensate for AM to PM distortion, then AM to PM distortion is partially compensated, but additional loading is introduced at the input of the PA and PA gain drops
Solution Approach 1:
The patent extracts the AM to PM distortion compensation function from the power amplifier input stage and relocates it to the intermediate frequency (IF) stage. By using an auxiliary vector modulator at the IF stage, the compensation is achieved without introducing additional loading at the PA input, thus avoiding the gain drop problem while still correcting the distortion
Solution Approach 2:
The patent introduces an auxiliary vector modulator as an intermediary device at the IF stage to compensate for AM to PM distortion. This intermediary approach allows distortion compensation to be achieved through signal processing before the PA, avoiding direct interaction with the PA input and thus preventing additional loading and gain loss
2Ease of operation
If IF gain is lowered at lower power to control gain, then gain control is achieved, but mm-Wave noise performance is limited
Solution Approach 1:
The patent segments the gain control function into two independent parts: IF gain control for ease of operation and mm-Wave gain control for noise performance. The auxiliary vector modulator handles IF gain adjustment without affecting the mm-Wave signal path, allowing the mm-Wave gain to remain high and preserve noise performance while still achieving the required overall gain control
Solution Approach 2:
The auxiliary vector modulator serves as an intermediary that provides gain control at the IF stage without impacting the mm-Wave signal path. This allows the system to achieve the desired gain control functionality while maintaining high mm-Wave gain for superior noise performance
3Manufacturing precision
If high linearity is achieved through traditional methods, then EVM requirements are met at maximum power, but AM to PM distortion limits EVM at maximum power region
Solution Approach 1:
The patent applies preliminary action by compensating for AM to PM distortion at the IF stage before the signal reaches the power amplifier. The auxiliary vector modulator pre-corrects the signal characteristics, so that when the signal passes through the PA, the distortion is already minimized, resulting in improved EVM at the maximum power region
Data Source
AI summary
A phase shifter including a quadrature generator configured to generate an in phase (I) signal and a quadrature (Q) signal from an input signal; an in phase vector modulator (VM_I) configured to receive the I signal and a quadrature vector modulator (VM_Q) configured to receive the Q signal; and an auxiliary VM_I connected to the VM_I and an auxiliary VM_Q connected to the VM_Q, the auxiliary VM_I configured to receive the I signal, the auxiliary VM_Q configured to receive the Q signal, the auxiliary VM_I and the auxiliary VM_Q configured to receive a bias signal and configured to adjust an in phase amplitude output of the VM_I and a quadrature amplitude output of the VM_Q responsive to the bias signal.