Variable Bandwidth Low-Pass Filter for EER Transmitter
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Solution Overview
Problem
Traditional RF transmitter architectures with linear power amplifiers are inefficient for evolving digital cellular systems using non-constant envelope modulation, and existing class-S modulators face challenges with bandwidth and stability, especially when handling multiple power amplifiers and varying modulation bandwidths.
Innovation Solution
A RF transmitter with a variable bandwidth low-pass filter and a pulse width modulator driven by a variable frequency clock, along with variable bypass capacitances, to optimize bandwidth and stability for multi-band and multi-mode operations, allowing for dynamic adjustment of filter settings based on the operating mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a fixed bandwidth low-pass filter is used in the class-S modulator, then the filter design is simple, but the bandwidth cannot be optimized for different modulation types and frequencies
Solution Approach 1:
The patent implements a variable bandwidth low-pass filter that can dynamically adjust its cutoff frequency based on the operating mode. The filter transitions from a fixed configuration to a dynamic one where the bandwidth is adjusted according to the specific modulation type and frequency requirements, allowing optimization for each operating condition without manual reconfiguration.
Solution Approach 2:
The patent changes the bandwidth parameter of the low-pass filter based on different operating modes. By adjusting the cutoff frequency parameter dynamically, the system adapts to different modulation schemes (e.g., GSM, EDGE, WCDMA) and frequency bands, achieving optimal performance for each mode while maintaining a single filter structure.
2Use of energy by moving object
If the clock frequency of the pulse width modulator is kept fixed, then the modulator operation is simple, but the efficiency degrades at low frequencies and narrow bandwidths
Solution Approach 1:
The patent implements a variable clock frequency for the pulse width modulator that dynamically adjusts based on the operating mode and bandwidth requirements. At low frequencies and narrow bandwidths, the clock frequency is reduced to improve efficiency, while at higher frequencies and broader bandwidths, the clock frequency increases to maintain performance, optimizing energy usage across all operating conditions.
Solution Approach 2:
The patent changes the clock frequency parameter of the pulse width modulator according to the specific operating mode and bandwidth requirements. This parameter adjustment allows the modulator to operate efficiently across different frequency ranges and bandwidths, preventing efficiency degradation that would occur with a fixed clock frequency.
3Stability of the object's composition
If bypass capacitances are fixed, then the circuit design is simple, but the stability is insufficient at low frequencies
Solution Approach 1:
The patent implements variable bypass capacitances that can be dynamically adjusted based on the operating frequency and mode. At low frequencies, larger capacitance values are selected to maintain stability, while at higher frequencies, smaller capacitance values are used. This dynamic adjustment ensures optimal stability across the entire operating range without requiring multiple fixed capacitor banks.
Solution Approach 2:
The patent changes the capacitance parameter of the bypass capacitors according to the operating frequency and mode requirements. By selecting appropriate capacitance values for each operating condition, the system achieves improved stability at low frequencies while maintaining proper operation across all frequency ranges, eliminating the need for complex multi-capacitor configurations.
Data Source
AI summary
A RF transmitter has at least one amplifier having an input terminal for receiving a phase modulated signal to be transmitted on an RF carrier and an input node for receiving a modulation signal for amplitude modulating the RF carrier. The RF transmitter further includes an amplitude modulator having an output coupled to the input node of the power amplifier through a low-pass filter. The low-pass filter includes at least one variable filter component for varying a bandwidth of the low-pass filter. In a preferred embodiment an envelope elimination and restoration (EER) RF transmitter includes at least one power RF amplifier having the input terminal for receiving the phase modulated signal to be transmitted on the RF carrier, and further including an input power node for receiving a modulated voltage for amplitude modulating the RF carrier. The EER RF transmitter further includes a class-S modulator having a variable bandwidth low-pass filter having an output coupled to the input power node and including at least one first variable capacitance.