Analog Baseband Filter Switching for Multimode Bandwidth Control
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Solution Overview
Problem
Multimode multiband radio transceivers face challenges in accurately configuring cutoff frequencies for analog filters due to variations in resistance and capacitance with temperature and process conditions, leading to increased circuit area and manufacturing costs, as well as signal degradation and noise issues.
Innovation Solution
The implementation of a filtering apparatus that shares capacitors and uses concatenated analog baseband filters, allowing for flexible resistance and capacitance control through digital algorithms, enabling support for various bandwidths and modes, including Carrier Aggregation, while reducing circuit area and enhancing noise cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large capacitance is used to process low band 2G signals, then the cutoff frequency accuracy is improved, but the circuit area increases
Solution Approach 1:
The patent implements dynamic switching between different capacitor configurations based on the operating mode. For 2G mode, capacitors are connected in parallel to achieve large capacitance values (e.g., 1000pF) required for accurate low-frequency cutoff. For 3G/4G mode, the same capacitors are reconfigured or switched to provide smaller capacitance values suitable for wideband operation. This dynamic reconfiguration allows a single circuit to achieve both large capacitance when needed and small area when not needed.
Solution Approach 2:
The analog baseband filter circuit is designed to serve multiple functions across different communication modes. The same physical capacitors and resistors are used for both 2G narrowband filtering and 3G/4G wideband filtering by changing their effective values through switching networks. This multi-functionality eliminates the need for separate filter circuits for different modes, reducing overall circuit area while maintaining the required large capacitance for 2G operation when activated.
2Measurement precision
If large capacitance is used to process low band 2G signals, then the cutoff frequency accuracy is improved, but the manufacturing cost increases
Solution Approach 1:
The circuit employs dynamic switching mechanisms that allow standard-value capacitors to function as large-capacitance components when needed for 2G mode. By using switching networks to connect multiple capacitors in parallel only during 2G operation, the design avoids the need to permanently integrate large, expensive capacitors into the circuit, thereby reducing manufacturing costs while maintaining cutoff frequency accuracy when required.
Solution Approach 2:
The patent changes the effective electrical parameters of the filter components through digital control. By switching between different capacitor configurations and adjusting resistor values via digital-to-analog converters, the circuit adapts its capacitance and resistance parameters to match the requirements of different communication modes. This parameter adjustment allows the use of smaller, cheaper capacitors that can be reconfigured to provide large capacitance values when 2G mode is active.
3Measurement precision
If separate filter circuits are provided for 2G and 3G/4G modes, then the cutoff frequency accuracy for each mode is improved, but the device complexity increases
Solution Approach 1:
The patent designs a universal analog baseband filter circuit that can operate in both 2G and 3G/4G modes with appropriate configuration. The same filter topology, capacitors, and resistors are used for both modes, with switching networks and digital control mechanisms that reconfigure the component values based on the active mode. This eliminates the need for separate physical filter circuits for different modes, reducing device complexity while maintaining cutoff frequency accuracy for each mode through proper parameter adjustment.
Solution Approach 2:
The filter circuit implements dynamic reconfiguration capabilities that allow it to adapt its characteristics for different communication modes. Switching networks dynamically connect or disconnect specific capacitors and resistors based on whether 2G or 3G/4G mode is active. Digital-to-analog converters dynamically adjust resistor values to provide the appropriate time constants for each mode. This dynamic adaptation allows a single circuit to replace multiple static filter circuits, reducing overall device complexity.
4Measurement precision
If the circuit area is increased to support 2G mode, then the cutoff frequency accuracy is improved, but the signal noise ratio deteriorates
Solution Approach 1:
The patent implements dynamic switching that activates large-capacitance configurations only when 2G mode is operational. During 3G/4G mode, the circuit uses smaller capacitance values and shorter wire lengths appropriate for wideband operation. This temporal separation ensures that the large circuit area and associated noise issues only exist when actually needed for 2G communication, while modern wideband modes benefit from the reduced noise characteristics of smaller capacitor configurations.
Solution Approach 2:
The filter circuit is designed with different local configurations optimized for different operating conditions. For 2G mode, specific regions of the circuit are activated with large capacitors and corresponding resistor values to achieve accurate narrowband filtering. For 3G/4G mode, different regions are activated with smaller capacitors and adjusted resistor values optimized for wideband operation. This local optimization allows each mode to operate with the most appropriate circuit characteristics, minimizing noise while maintaining accuracy.
Data Source
Figure 1~2a
Figure 2b~3a
Figure 3b
AI summary
A filtering apparatus and method of a multimode multiband transceiver is provided for filtering a signal carrying an analog baseband signal. A filtering apparatus of a multimode multiband radio transceiver of the present invention includes a filtering unit which filters Radio Frequency (RF) signals on one of at least one frequency bands, a switching unit which switches the signals among at least one filter block included in the filtering unit according to a selected communication mode, and a controller which selects the communication mode and controls the switching unit. The analog signal filtering apparatus and method of the present invention is advantageous in terms of providing a variable gain amplifier, filter circuit, and algorithm capable of fulfilling the gains and bandwidths required by the baseband receiver for all mobile communication standards complied by 2G, 3G, and 4G systems.