Hybrid VGA Power Control for Fast, Accurate Transmitter Output
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Solution Overview
Problem
Existing variable gain amplifiers (VGAs) in communication systems face challenges in achieving accurate output power control due to difficulties in meeting step accuracy and slope linearity specifications, especially in open loop modes, and suffer from reduced phase margin and non-linear closed loop bandwidth in closed loop modes, leading to complex circuitry and increased current consumption.
Innovation Solution
A hybrid closed loop power control system that combines open loop and closed loop modes, using a variable gain amplifier (VGA) with a hybrid power control loop (HPCL) that adjusts gain directly in open loop mode and employs digital feedback in closed loop mode to achieve fine gain step accuracy, minimizing circuit complexity and current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a VGA controls output power directly in open loop mode, then the control response is fast, but the step accuracy and slope linearity specifications become difficult to meet
Solution Approach 1:
The patent segments the power control function into two parts: a PGA (programmable gain amplifier) handling coarse gain adjustment in open-loop mode for fast response, and a VGA (variable gain amplifier) handling fine gain adjustment in closed-loop mode for high precision. This segmentation allows each component to optimize for its specific function, resolving the contradiction between speed and precision.
Solution Approach 2:
The patent introduces a closed-loop feedback mechanism where the output power is monitored and fed back to adjust the VGA gain. This feedback ensures that the final output power meets the required step accuracy and slope linearity specifications, compensating for the limitations of open-loop control while maintaining fast response through the PGA's initial coarse adjustment.
2Manufacturing precision
If a VGA is controlled in closed loop mode, then the output power accuracy is improved, but the control slope varies causing non-linear closed loop bandwidth and reduced phase margin
Solution Approach 1:
The patent segments the gain control range into coarse (PGA) and fine (VGA) portions. The PGA handles the majority of gain adjustment with fixed characteristics, while the VGA handles small incremental adjustments with controlled gain steps. This segmentation prevents the control slope from varying significantly, maintaining stable closed-loop bandwidth and phase margin while achieving high output power accuracy.
Solution Approach 2:
The patent implements a hybrid control mode that dynamically switches between open-loop PGA control and closed-loop VGA control. The system uses open-loop mode for large gain changes and closed-loop mode for fine adjustments, optimizing both response speed and accuracy while maintaining stability through controlled transition between modes.
3Manufacturing precision
If tight analog design specifications are used to control VGA slope characteristics, then the power control accuracy is improved, but the circuit complexity and current consumption increase
Solution Approach 1:
The patent segments the gain control function between PGA and VGA, allowing the VGA to operate with relaxed specifications since it only needs to handle fine adjustments. The PGA handles the bulk of gain control with simpler digital programming, reducing the precision requirements for the analog VGA circuitry and thereby reducing overall circuit complexity and current consumption.
Solution Approach 2:
The patent introduces a gain control unit that acts as an intermediary, managing the transition between PGA and VGA and coordinating their operation. This intermediary layer simplifies the control logic by abstracting the complexity of switching between open-loop and closed-loop modes, and by managing the handoff between coarse and fine gain control, reducing the overall system complexity.
Data Source
AI summary
Systems and method for implementing a transmitter with hybrid closed loop power control in a communication device.