Passive DAC Filter Topology for Lower Low-Frequency Output Impedance
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Solution Overview
Problem
Existing passive low-pass filter systems for pulse density digital-to-analog converters have high output impedance, which increases errors and are costly in terms of component count, current consumption, and chip size, while also being inefficient in terms of component costs and size.
Innovation Solution
A passive low-pass filter system comprising a resistor-capacitor circuit with a positive voltage input connected to a low-pass filter and a negative voltage input connected to a high-pass filter, where the output impedance at DC and low-frequency is reduced by half compared to prior art systems, maintaining the same transfer function and corner frequency, and utilizing two digital-to-analog converters to generate the necessary voltage inputs with minimal additional costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high order passive filter is used to suppress high frequency content, then filtering performance is improved, but output impedance increases causing additional errors
Solution Approach 1:
The filter is divided into two separate first-order filters (low-pass and high-pass) that operate in parallel rather than using a single high-order filter. This segmentation maintains effective high-frequency suppression while keeping the output impedance low, as each first-order filter has lower impedance characteristics.
2Device complexity
If passive filters are used instead of active filters, then cost and chip size are reduced, but output impedance increases
Solution Approach 1:
By segmenting the filter into two first-order passive filters working in parallel, the system maintains the cost and simplicity advantages of passive filters while achieving low output impedance through the parallel configuration, thereby improving signal accuracy.
3Manufacturing precision
If a series connection of two RC low-pass filters is used, then second order filtering is achieved, but output impedance becomes high
Solution Approach 1:
Instead of connecting the two first-order filters in series (which would increase impedance), the invention inverts the approach by connecting them in parallel. This parallel configuration achieves the desired second-order filtering effect while maintaining low output impedance, as parallel connections reduce overall impedance.
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 proposed solution achieves a significant reduction in output impedance at DC and low-frequency, improving signal fidelity and reducing errors while maintaining cost efficiency and component count similarity to prior art systems, thus enhancing the performance and reliability of pulse density digital-to-analog converters.
Implementation Method 1
the output impedance of the reconstruction filter causes an additional error
Implementation Method 2
A series connection of two resistor-capacitor (RC) low-pass filters
Data Source
Figure 1~3
Figure 4a~4b
Figure 5
AI summary
The invention refers to a passive low-pass filter system (1) for pulse density digital-to-analog converters, comprising a positive voltage input (Vin), a negative voltage input (-Vin), a voltage output (Vout), a first low-pass filter (6) and a second high-pass filter (7), wherein the positive voltage input (Vin) is connected to the first low-pass filter (6), the voltage output (Vout) corresponds to the output of the first low-pass filter (6), the negative voltage input (-Vin) is connected to the second high-pass filter (7) and the output of the second high-pass filter (7) is connected to the voltage output (Vout).