Receiver Filter Switching for Fast Gain Setting Without Muting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The direct conversion scheme in receivers for wireless communication faces signal degradation due to flicker noise and DC offset, which requires input signal muting during cutoff frequency changeover, hindering high-speed gain setting and increasing physical size due to large capacitance and resistance values needed for low-frequency filtering.
Innovation Solution
A filter circuit with a first and second filter, each with distinct cutoff frequencies, and a charging circuit that allows for quick switching between them without muting the input signal, using a series of switches and capacitors to control the cutoff frequencies and charge the capacitors, enabling high-speed gain setting and reduced DC offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a highpass filter with low cutoff frequency is used to remove DC offset, then DC offset removal is improved, but physical size increases due to larger capacitance and resistance values
Solution Approach 1:
The filter is divided into two separate filters with different cutoff frequencies. The first filter has a higher cutoff frequency for fast transient response, while the second filter has a lower cutoff frequency for better DC offset removal. This segmentation allows each filter to be optimized for its specific function without requiring large component values in both filters simultaneously.
Solution Approach 2:
The cutoff frequency of the filter is made dynamically switchable between two values based on the signal conditions. During transient periods, the higher cutoff frequency is used for fast response. During steady-state periods, the lower cutoff frequency is used for better DC offset removal. This dynamic adjustment eliminates the need for always using large component values.
2Object-affected harmful factors
If cutoff frequency is changed over to remove DC offset, then DC offset removal is improved, but signal reception is interrupted during the changeover period
Solution Approach 1:
The capacitor is pre-charged through the charging circuit before the cutoff frequency changeover. This preliminary charging action ensures that when the switch transitions from the first filter to the second filter, the capacitor already has the appropriate voltage level, preventing transient signals and avoiding the need for signal muting during changeover.
Solution Approach 2:
The charging circuit acts as an intermediary mechanism that prepares the capacitor for the upcoming filter switch. By providing a dedicated charging path with appropriate time constants, it ensures the capacitor is ready for the transition, allowing seamless frequency changeover without interrupting signal reception.
3Object-affected harmful factors
If large capacitance values are used in the highpass filter, then DC offset removal is improved, but settlement time increases
Solution Approach 1:
The filtering function is segmented into two filters with different characteristics. The first filter uses smaller capacitance values for fast transient response and short settlement time. The second filter uses larger capacitance values for effective DC offset removal but is only activated during steady-state conditions. This segmentation allows the system to achieve both fast settlement and effective DC offset removal at different times.
Solution Approach 2:
The filter operates in periodic cycles, switching between the first filter during transient periods and the second filter during steady-state periods. This periodic switching allows the system to use small capacitance values when fast response is needed and large capacitance values when DC offset removal is the priority, optimizing both settlement time and filtering performance.
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
Enables high-speed gain setting and reduced DC offset without the need for input signal muting, maintaining a compact design by minimizing the physical size of filter components and reducing settlement time.
Implementation Method 1
a second capacitor C2X and a second resistor R2X, a second filter switch circuit (SW3X, SW5X) for coupling the second filter (C2X, R2X) on the signal path (Xin:Xout)
Data Source
AI summary
Gain setting can be performed at high speed while reducing DC offset due to a filter cutoff frequency changeover without the need for input signal muting. A filter circuit having first and second filters is capable of allowing settings of first and second cutoff frequencies. First and second filter switch circuits and a charging circuit including a charging resistor and a charging switch are provided. For a first time period, the first switch circuit is controllably turned on while the second switch circuit is controllably turned off, thereby providing the first filter function. For a second time period, the first switch circuit is controllably turned off while the second switch circuit is controllably turned on, thereby providing the second filter function. For the first time period, the charging switch is controllably turned on so that the second capacitor is charged via the charging resistor.