Tunable Filter Clock Spreading for GSM Harmonic Interference
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Solution Overview
Problem
In radiotelephones, the harmonics of clock signals interfere with radio communications, particularly in GSM channels, due to the difficulty in providing adequate shielding for clock signals and their harmonics.
Innovation Solution
A spectrum spreader is used to generate a spread spectrum clock signal by employing a tunable filter with an inductor-capacitor band pass filter and a varactor diode, controlled by a signal generator to spread the frequency of the clock signal above and below its original frequency, reducing interference with communications channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reference crystal is used to generate a clock signal for the processor, then the processor can operate with a stable clock frequency, but harmonics of the clock signal interfere with radio signals received at the radiotelephone
Solution Approach 1:
The patent applies parameter changes by modifying the frequency characteristics of the clock signal through a spectrum spreader. The spreader varies the clock frequency over time according to a spreading code, transforming the concentrated harmonic energy at a single frequency into distributed energy across a broader frequency spectrum. This reduces the peak harmonic interference at specific GSM channels while maintaining the overall clock signal stability needed for processor operation.
2Object-generated harmful factors
If adequate shielding is provided for the clock signal and its harmonics, then interference with radio signals is reduced, but the device complexity and difficulty of implementation increase
Solution Approach 1:
The patent replaces the mechanical/physical shielding approach with an electronic signal processing solution. Instead of using physical barriers (shielding) to block harmonic interference, the invention uses a spectrum spreader to electronically modify the clock signal's frequency characteristics. This substitution eliminates the need for complex EMI shielding structures while achieving the same goal of reducing harmonic interference with radio signals.
3Object-generated harmful factors
If the clock signal frequency is spread above and below the original frequency, then harmonic interference at specific channels is reduced, but the processor must operate with a variable frequency clock signal
Solution Approach 1:
The patent applies dynamics by making the clock signal frequency variable rather than fixed. The spectrum spreader dynamically adjusts the clock frequency according to a spreading code, causing the frequency to fluctuate above and below the original center frequency. This dynamic frequency variation spreads the harmonic energy across multiple frequencies, reducing concentrated interference at specific GSM channels while the processor adapts to operate with this dynamically varying clock signal.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces interference by spreading harmonic components over different frequencies, thereby minimizing aggregate interference at specific channel frequencies and reducing the need for EMI shielding, allowing for proper operation of the processor and other components.
Implementation Method 1
The capacitive circuit may include a capacitor and a varactor diode coupled in series between the signal conductor and the reference voltage
Implementation Method 2
The tunable filter may include an inductor-capacitor (LC) band pass filter, for example, having an inductive circuit and a capacitive circuit coupled in parallel
Data Source
AI summary
A spectrum spreader may include a signal conductor and a tunable filter. The signal conductor may be configured to receive a clock signal having a clock signal frequency. The tunable filter may be coupled to the signal conductor wherein the tunable filter is configured to spread a frequency of the clock signal responsive to a control signal to provide a spread spectrum clock signal. More particularly, a frequency of the spread spectrum clock signal may be spread relative to the clock frequency. Related communications devices and methods are also discussed.