Multi-Mode High-Pass Filter for Artifact-Free Multipath ADCs
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Solution Overview
Problem
Existing multipath analog-to-digital converters (ADCs) and analog front ends (AFEs) face challenges in smooth transitioning and scaling to integrated circuit levels, leading to undesirable signal artifacts and inefficiencies in audio applications.
Innovation Solution
A system with multiple processing paths and control circuitry that includes a high-pass filter with a switched-capacitor resistor, capable of operating in high-impedance and low-impedance modes, to generate weighted digital signals based on the analog input signal characteristics, reducing signal artifacts and improving dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multipath ADCs/AFEs are used to optimize separate processing paths for small and large amplitude signals, then dynamic range and noise performance are improved, but signal artifacts occur during path transitions
Solution Approach 1:
The high-pass filter impedance is dynamically adjusted based on the signal amplitude being processed. The filter operates in different impedance modes (high, medium, low) that are selected according to the input signal level, allowing smooth adaptation between processing paths without generating artifacts. This dynamic adjustment is controlled by monitoring the signal amplitude and switching the filter impedance accordingly.
Solution Approach 2:
The patent changes the impedance parameter of the high-pass filter to optimize performance for different signal amplitudes. By adjusting the filter impedance rather than switching entire processing paths, the system maintains continuous operation and avoids the artifacts associated with abrupt path transitions. The impedance parameter is modified based on the detected signal amplitude level.
2Area of stationary object
If circuitry is scaled to integrated circuit level, then area and power consumption are reduced, but existing multipath AFE/ADC approaches do not scale well
Solution Approach 1:
The high-pass filter is designed with multi-functionality to handle different signal amplitude ranges by adjusting its impedance. This single filter structure replaces the need for separate filtering circuits in different processing paths, enabling better integration and scaling to IC level. The filter serves multiple functions across different operating conditions, reducing overall circuit complexity and area.
Solution Approach 2:
The switched-capacitor implementation of the high-pass filter allows for compact nesting of circuit elements. The filter components are integrated within the IC structure with capacitors and switches arranged in a nested configuration that minimizes area while maintaining performance. This nested arrangement enables the filter to be incorporated into the IC without significantly increasing area or compromising manufacturability.
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
The solution enhances signal processing by reducing artifacts and improving dynamic range, allowing for efficient scaling to integrated circuit levels while maintaining low noise and power consumption.
Implementation Method 1
a switched-capacitor resistor coupled to the output. The input, the output, the capacitor, and the switched-capacitor resistor may be arranged to generate the output signal as a high-pass filtered version of the input signal. The high-pass filter may be configured to operate in a plurality of modes comprising at least a high-impedance mode in which the control circuitry causes the switching frequency of switched capacitors of the switched-capacitor resistor to be such that the switched-capacitor resistor has a first resistance and a low-impedance mode in which the switched-capacitor resistor has a second resistance significantly smaller than first resistance
Data Source
AI summary
A system may comprise a high-pass filter having an input for receiving an input signal, an output for generating an output signal, a capacitor coupled between the input and the output, a switched-capacitor resistor coupled between the output and a reference voltage, and control circuitry configured to control the reference voltage to cancel current leakage into a circuit coupled to the output. The input, the output, the capacitor, and the switched-capacitor resistor may be arranged to generate the output signal as a high-pass filtered version of the input signal and the high-pass filter may be configured to operate in a plurality of modes comprising at least a high-impedance mode and a low-impedance mode in which the resistance of the switched-capacitor resistor is significantly smaller than the resistance when in the high-impedance mode.A system may include a plurality of processing paths having a first path configured to generate a first digital signal based on an analog input signal and a second path configured to generate a second digital signal based on the analog input signal, the second path having a high-pass filter for filtering the analog input signal prior to the analog input signal being processed by the remainder of the second path, and the high-pass filter having a corner frequency. Control circuitry may be configured to determine frequency-dependent weighted proportions of the first and second digital signals to be combined into an output digital signal based on a characteristic of the analog input signal. Frequency-dependent weighted proportions may be such that the digital output signal includes spectral content of the first digital signal below the corner frequency to account for spectral content of the second digital signal below the corner frequency being filtered.A system may include an input for receiving an input signal, an output for generating an output signal, a capacitor coupled between the input and the output, a variable resistor coupled to the output and having a plurality of modes including a first mode in which the variable resistor has a first resistance and a second mode in which the variable resistor has a second resistance, and control circuitry configured to determine a difference between the input signal and the output signal and switch between modes of the plurality of modes when the difference is less than a predetermined threshold.