PLL Compensation Filter for Transmitter Bandwidth Expansion
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Solution Overview
Problem
Phase locked loops 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 bandwidth, pre-distorting signals to counteract the lowpass filtering effect of the phase locked loop, resulting in a Butterworth filter response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a phase locked loop is used in the transmitting device, then the signal phase and frequency stability is improved, but the bandwidth of the signal path is reduced
Solution Approach 1:
The compensation filter is placed before the phase locked loop in the signal path to pre-distort the signal in a way that counteracts the bandwidth-limiting effect of the PLL. This preliminary action allows the signal to pass through the PLL with reduced degradation, effectively expanding the usable bandwidth while maintaining the PLL's phase and frequency stability benefits.
Solution Approach 2:
The compensation filter acts as an intermediary component between the signal source and the phase locked loop. It modifies the signal characteristics before entry into the PLL, creating a compensated signal that the PLL can process more effectively, thereby resolving the bandwidth-stability tradeoff.
2Device complexity
If a phase locked loop with limited bandwidth is used, then the circuit complexity is reduced, but the signal fidelity is degraded
Solution Approach 1:
The compensation filter performs preliminary signal conditioning before the signal enters the phase locked loop. By pre-adjusting the signal spectrum and phase characteristics, the filter enables the simple PLL circuit to achieve better signal fidelity output than it would without the compensation stage.
Data Source
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.