Switched Capacitor Mixer Filter for Low-Noise Wireless Receivers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In high-integration signal processing systems, integrating analog functions on chips is limited by economic considerations, such as the need for high-value capacitors, and existing switched capacitor filters face challenges in achieving sufficient gain and noise reduction while maintaining linearity, especially in wireless receivers.
Innovation Solution
A dynamically configurable passive switched capacitor filter with multiple sections and stacked capacitors, operated by MOSFET switches, which provides amplification and filtering, and is designed to support various wireless standards by adjusting capacitance and filter coefficients dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-value capacitors are used in analog circuits, then filtering performance and noise reduction are improved, but chip area and manufacturing complexity increase significantly
Solution Approach 1:
The patent transforms the continuous-time analog filter into a discrete-time switched capacitor filter, changing the fundamental operating parameter from continuous voltage to switched charge packets. This allows the use of small capacitors (e.g., 1-10 pF) instead of large capacitors, reducing chip area while maintaining filtering performance through temporal switching operations.
Solution Approach 2:
The patent replaces the traditional passive RC filter mechanism with an active switched capacitor mechanism controlled by clock signals. The filtering function is achieved through periodic charge transfer and accumulation in the integrator stage, substituting the continuous resistive-capacitive time constant with a discrete switching-based time constant determined by clock frequency and capacitor ratios.
2Power
If gain is increased in the front-end amplifier, then signal strength is improved, but noise and linearity degradation worsen
Solution Approach 1:
The patent performs filtering and signal conditioning at the input stage before the signal is amplified and processed further. The switched capacitor filter operates on the raw input signal to establish the correct spectral content and impedance characteristics early in the signal chain, allowing subsequent amplification stages to operate with better linearity and lower noise figures.
Solution Approach 2:
The patent divides the signal processing function into separate stages: a dedicated switched capacitor filter stage for frequency selection and impedance matching, followed by amplification stages. This segmentation allows each stage to be optimized independently, with the filter stage handling frequency selection and the amplifier stages handling gain, thereby improving overall linearity and noise performance.
3Area of stationary object
If switched capacitor filters are used instead of traditional RC filters, then chip area is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the filter design from absolute capacitor value dependence to capacitor ratio dependence. By expressing filter poles and zeros in terms of ratios between capacitors in the switched capacitor network, the design becomes insensitive to absolute capacitor value variations due to manufacturing tolerances, requiring only precise matching of capacitor ratios which can be achieved through correlated trimming or laser adjustment.
Data Source
AI summary
A multi-tap direct sub-sampling mixing system for wireless receivers is provided with a dynamically configurable passive switched capacitor filter. A front end amplifier is connected to receive a signal. The passive switched capacitor filter is connected to receive the amplified signal and has an output for providing a filtered signal. The switched capacitor filter has at least two sections that are each operable as a pole, wherein a first section of the at least two sections has sets of at least two stacked capacitors interconnected with a set of switches operable to amplify in input voltage provided to an input of the first section in response to operation of the set of switches; and a back end section connected to the output of the switched capacitor filter to receive the filtered signal.