Parallel Filter Switch Layout for Parasitic Capacitance Matching
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Solution Overview
Problem
High-pass filters in switching configurations suffer from parasitic capacitance that cause deviations in output signals, affecting phase flatness and impedance matching.
Innovation Solution
The placement of switches after capacitors in the signal path ensures that parasitic capacitances are common to both high-pass and low-pass paths, allowing for the use of a matching network to cancel or offset their effects, thereby maintaining impedance matching and phase flatness across frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-pass filter is employed in a switching configuration in parallel with another filter, then the filter can pass high-frequency signals while blocking low-frequency signals, but parasitic capacitance causes changes in the output signal from the desired value
Solution Approach 1:
A switching network is introduced as an intermediary component between the high-pass filter and the output. This switching network selectively connects or disconnects the high-pass filter from the output based on frequency conditions, thereby mediating the harmful effect of parasitic capacitance by controlling when the filter is active in the signal path
Solution Approach 2:
The switching network changes the circuit configuration parameter (connected vs. disconnected state) based on signal frequency characteristics. By dynamically altering the circuit topology through switching, the system adapts to minimize parasitic capacitance effects while maintaining high-pass filtering functionality when needed
2Device complexity
If switches are placed before capacitors in the signal path, then the switching configuration is simpler, but parasitic capacitances are not common to both paths and cannot be easily canceled
Solution Approach 1:
Instead of placing switches before capacitors (conventional approach), the patent inverts the sequence by placing switches after capacitors in the signal path. This inversion ensures that parasitic capacitances are common to both the high-pass and low-pass paths, enabling them to be canceled by a matching network and improving impedance matching consistency
3Ease of manufacture
If parasitic capacitances are not common to both filter paths, then the filter design is more straightforward, but impedance matching and phase flatness cannot be maintained across frequencies
Solution Approach 1:
The patent merges the parasitic capacitances from both the high-pass and low-pass paths by configuring switches after capacitors, so that both paths share common parasitic capacitance elements. This merging enables the use of a single matching network to cancel parasitic effects in both paths simultaneously, maintaining phase flatness across frequencies while keeping the design practical
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 impact of parasitic capacitances, ensuring consistent phase shift and impedance matching across a wide frequency range, enhancing the performance of phase shifters and high-pass filter banks.
Implementation Method 1
The high-pass filter contains a first capacitor and a first inductor
Implementation Method 2
The high-pass filter contains a first capacitor and a first inductor
Implementation Method 3
A first switch and a second switch respectively control whether or not the first path and the second path pass the input signal
Data Source
AI summary
Aspects of the present disclosure are directed to a circuit that generates an output signal on an output node from an input signal received on an input node. The circuit contains a first path containing a high-pass filter and a second path containing another filter, both of the first path and the second path being provided in parallel between the input node and the output node. A first switch and a second switch respectively control whether or not the first path and the second path pass the input signal to generate the output signal, where only one of the first switch and the second switch is configured to permit a corresponding path to pass the input signal at any specific time. The high-pass filter contains a first capacitor and a first inductor, with the first switch being coupled between the first capacitor and the first inductor in the first path.