Dual Down Converter Frequency Coordination Against Spurious IF Coupling
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Solution Overview
Problem
In universal dual configuration down converters, the inability to change the oscillation frequency of one mixer without affecting the other leads to spurious signal coupling, causing the tuner to erroneously receive the spurious signal as an IF signal.
Innovation Solution
The down converter employs separate amplification units and down converter circuits for each polarized wave signal, with frequency-divided local oscillation signals ensuring the difference frequency is beyond the receive frequency band of the receiver, thus preventing spurious signal coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If both local oscillation circuits function simultaneously to output IF signals to two tuners, then the down converter can provide universal dual configuration capability, but spurious signal coupling occurs between signal lines
Solution Approach 1:
The patent changes the oscillation frequency parameter of the second local oscillation circuit to a frequency that does not cause spurious signal coupling with the first signal line. Specifically, the second local oscillation frequency is set outside the frequency band that would couple into the first signal line, thereby maintaining universal dual configuration capability while eliminating the harmful spurious signal coupling effect.
2Object-generated harmful factors
If the oscillation frequency of the second local oscillation circuit is changed to prevent spurious signal coupling, then spurious signal influence is reduced, but the frequency must be carefully controlled to avoid overlapping with receive frequency bands
Solution Approach 1:
The patent sets the second local oscillation frequency to a specific value or range that satisfies two conditions: (1) it prevents spurious signal coupling with the first signal line, and (2) it ensures the difference frequency between the second local oscillation frequency and the first local oscillation frequency does not overlap with the receive frequency band of the first tuner. This parameter optimization resolves the contradiction between reducing spurious signals and maintaining reliable frequency band separation.
3Ease of operation
If separate local oscillation circuits are used for each signal line, then each circuit can function independently, but frequency interference between circuits cannot be avoided
Solution Approach 1:
The patent maintains independent local oscillation circuits for each signal line but introduces frequency coordination through parameter optimization. The second local oscillation frequency is specifically set to avoid generating spurious signals that would couple into the first signal line, while still allowing both circuits to function independently for their respective tuners.
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 configuration effectively reduces the influence of spurious signals, enabling the down converter to output multiple IF signals without erroneous reception by the tuner.
Implementation Method 1
a first local oscillation unit for generating a first local oscillation frequency signal using the first reference signal
Implementation Method 2
a first frequency-divider for generating a first frequency-divided signal obtained by frequency dividing the first local oscillation frequency signal
Implementation Method 3
a first frequency conversion unit for converting a signal amplified by the amplification unit into a first intermediate frequency signal using the first frequency-divided signal
Implementation Method 4
a second local oscillation unit for generating a second local oscillation frequency signal using the second reference signal
Implementation Method 5
a second frequency-divider for generating a second frequency-divided signal obtained by frequency dividing the second local oscillation frequency signal
Implementation Method 6
a second frequency conversion unit for converting a signal amplified by the amplification unit into a second intermediate frequency signal using the second frequency-divided signal
Data Source
AI summary
A down converter has two down converter circuits. The one down converter circuit has a first mixer, a first ½ frequency-divider, and a first PLL. The other down converter circuit has a second mixer, a second ½ frequency-divider, and a second PLL. A difference frequency between a frequency of a local oscillation frequency signal of the second PLL and a frequency of a frequency-divided signal of the first ½ frequency-divider is higher than an upper limit of a receive frequency band of a tuner.