Switched-Capacitor High-Pass Coupling for Low Corner Frequency
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Solution Overview
Problem
Existing high-pass coupling circuits face challenges in achieving a low corner frequency while minimizing physical size, cost, and THD (Total Harmonic Distortion) noise, especially when dealing with large capacitors required for high tolerance across a wide range of frequencies and amplitudes.
Innovation Solution
A filter circuit utilizing charge storage elements and switch elements, controlled by a sequencing mechanism to perform time-sampled continuous value signal processing, implementing an infinite-impulse-response (IIR) filter with a high-pass configuration that can adjust its corner frequency and scale charges among elements, allowing for efficient coupling of signal processing blocks with reduced capacitor size and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a large capacitor is used to achieve a low corner frequency (e.g., 20 Hz) with a 1kΩ resistor, then the corner frequency requirement is met, but the physical size and cost increase significantly
Solution Approach 1:
The patent changes the operating parameters by using a switched-capacitor architecture where the effective capacitance is synthesized through switching operations at a higher frequency. Instead of using a single large capacitor (8 μF), the circuit uses smaller capacitors (e.g., 100 fF to 10 pF range) that are switched at frequencies much higher than the corner frequency (e.g., 100 kHz clock frequency), thereby achieving the same low-pass filter effect with much smaller physical components.
Solution Approach 2:
The patent employs periodic switching of capacitor connections to synthesize the equivalent of a large capacitor using smaller capacitors. The switch elements periodically connect and disconnect capacitor arrays during different phases of the clock cycle, creating an effective capacitance that is much larger than any individual capacitor in the array, thus achieving low corner frequencies without requiring large physical capacitors.
2Reliability
If a large capacitor is used to achieve high tolerance across a wide range of frequency and amplitude, then the filtering performance is improved, but the cost increases (e.g., more than $1.00 per capacitor in lots of 1000)
Solution Approach 1:
The patent transforms the problem from requiring a single large, high-tolerance capacitor to using multiple smaller capacitors with relaxed tolerance requirements. The switched-capacitor architecture allows the use of standard-value capacitors (e.g., 10% or 20% tolerance) in the femtofarad to picofarad range, which are significantly cheaper and more readily available than large 8 μF high-tolerance capacitors.
Solution Approach 2:
The patent divides the function of a single large capacitor into multiple smaller capacitors that are switched in parallel during different phases. This segmentation allows each individual capacitor to have relaxed tolerance specifications while the aggregate behavior of the switched network achieves the required filtering performance, thereby reducing component cost.
3Adaptability or versatility
If a switched capacitor filter is used to achieve a low corner frequency as a fraction of clock frequency (e.g., 1/1000 ratio), then the corner frequency can be adjusted, but the device complexity increases and single-ended signal paths are limited
Solution Approach 1:
The patent designs a universal switched-capacitor filter architecture that can handle both single-ended and differential signal paths. The same basic building blocks (switched capacitor cells, charge transfer networks, and feedback mechanisms) are used regardless of whether the input is single-ended or differential, thereby reducing design complexity while maintaining flexibility for different signal types and corner frequency requirements.
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 enables a high-pass filter with a corner frequency significantly lower than the sample period, reducing physical size and cost, while maintaining performance, and allows for flexible configuration to adapt to different signal conditions, simplifying the design of interconnection blocks.
Implementation Method 1
a first charge storage element having a first capacitance coupled to a second charge storage element having a second capacitance
Implementation Method 2
In phase B, a second configuration of the switch elements causes a charge sharing between the first charge storage element and the second charge storage element
Data Source
AI summary
A filter provides high-pass coupling between circuits. The filter includes charge storage elements and switch elements coupling the charge storage elements. A controller is coupled to the switch elements for sequencing configurations of the switch elements in phases for each of a succession of sample periods to perform a time sampled continuous value signal processing of the input signal to form the processed signal. The sequenced configurations include a configuration in which a charge representing a value of the input signal is stored on a multiple of the charge storage elements, a configuration in which charge storage elements are coupled with the switch elements, and a set of one or more configurations that implement a scaling of a charge on one of the charge storage elements to be on one or more of the charge storage elements.