Differential FIR Filter Layout for Negative Coefficients
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Solution Overview
Problem
Conventional finite impulse response (FIR) filters are limited by their inability to implement negative coefficients, which restricts their frequency response capabilities, and existing differential output filters require twice the number of resistors to achieve negative coefficients.
Innovation Solution
Designing a method for FIR filters that produces a differential output capable of having negative coefficients using approximately half the number of resistors, by determining Fourier coefficients, calculating impedance values, constructing an inverting delay line, and connecting impedance devices to differential buffers based on coefficient signs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional FIR filter circuit is used with positive coefficients only, then the circuit structure is simple, but the frequency response capability is limited
Solution Approach 1:
The patent applies inversion by using the complement output of the differential buffer to represent negative coefficients. Instead of adding separate negative coefficient paths, the invention inverts the output signal path and uses the complementary output to achieve negative weighting, thereby expanding frequency response capability without proportionally increasing circuit complexity
Solution Approach 2:
The differential buffer structure serves multiple functions: it provides both non-inverting and inverting outputs, enabling the same hardware to support both positive and negative coefficients. This multi-functionality allows the filter to achieve enhanced frequency response capability while reusing the same buffer infrastructure for different coefficient types
2Adaptability or versatility
If a differential output filter is designed to implement negative coefficients, then the frequency response capability is improved, but the number of resistors doubles
Solution Approach 1:
The patent merges the positive and negative coefficient paths by using a single set of resistors that serve both functions. The differential buffer's complementary output allows the same resistors to contribute to both positive and negative coefficient terms, effectively halving the resistor count while maintaining negative coefficient capability
Solution Approach 2:
Instead of creating a complete duplicate set of resistors for negative coefficients, the invention uses the complement output to create a virtual copy of the positive coefficient path. This allows negative coefficients to be implemented without physically duplicating the resistor network, reducing component count while achieving the desired functionality
Data Source
AI summary
A finite impulse response (FIR) filter having a differential output and capable of having negative coefficients, and a method of designing the filter, is disclosed. In contrast to the prior art, in which two output signals requires the use of two identical sets of impedance devices corresponding to the Fourier coefficients that create the desired response of the filter, the described method and system uses only a single set of impedance devices, and thus approximately one-half of the number of impedance devices used in the prior art. This is accomplished by appropriately selecting which resistors contribute to which output, so that a differential output may be obtained that is substantially the same as if impedance devices corresponding to all of the coefficients were used for each signal.