PLL Compensation Filter for Transmitter Bandwidth Expansion
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Solution Overview
Problem
Phase locked loops (PLLs) in wireless signal transmitting devices, such as VSATs, limit bandwidth, leading to degraded signal fidelity and poorer performance compared to receiving devices.
Innovation Solution
A compensation filter is implemented in the signal path of the transmitting device, programmed with coefficients and parameters to expand the PLL bandwidth, using a digital FIR Gaussian filter to pre-distort signals and maintain original signal integrity through the antenna connector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a phase locked loop is used in a transmitting device, then signal stability and frequency control are improved, but bandwidth is reduced leading to degraded signal fidelity
Solution Approach 1:
The compensation filter performs preliminary action by pre-distorting the signal before it enters the PLL. The filter applies inverse characteristics of the PLL's bandwidth limitation, so that when the signal passes through the PLL, the pre-applied compensation restores the original signal characteristics, effectively expanding the usable bandwidth while maintaining signal fidelity
Solution Approach 2:
The invention changes the parameters of the transmitting device by introducing a compensation filter with programmable coefficients. These coefficients are configured to match the specific PLL characteristics, allowing the system to adaptively compensate for bandwidth limitations and improve signal fidelity without sacrificing the stability provided by the PLL
2Reliability
If the phase locked loop bandwidth is reduced for stability, then frequency control is improved, but the transmitting device performance deteriorates compared to receiving device
Solution Approach 1:
The compensation filter applies preliminary distortion to the modulating signal that is the mathematical inverse of the PLL's bandwidth-limiting effect. This pre-compensation ensures that after the signal passes through the PLL, the overall response matches the desired frequency response, thereby maintaining transmitting device performance comparable to receiving devices
Solution Approach 2:
The system employs feedback by measuring the actual PLL frequency response and using this information to configure the compensation filter coefficients. This closed-loop approach ensures that the compensation is precisely tailored to the specific PLL implementation, optimizing both frequency control and transmitting performance
Data Source
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AI summary
An apparatus for PLL bandwidth expansion including a compensation filter and a phase locked loop, where the compensation filter is programmed with a compensation function derived based on programmable coefficients and parameters of a transmitting device, a frequency response of the phase locked loop, and a wanted frequency response.