Feedforward Analog Conditioning for ADC Anti-Aliasing
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Solution Overview
Problem
Current anti-aliasing filters face challenges in meeting stringent requirements without increasing total harmonic distortion (THD) or incurring significant area and power costs, especially when directly connected to ADCs without programmable gain amplifiers or active low pass filters.
Innovation Solution
An analog conditioning circuit with a feedforward signal path that attenuates undesired frequencies, allowing for increased resistance without affecting the main signal path's THD, by subtracting the filtered signal from the original signal, thus improving anti-aliasing performance without impacting THD.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the capacitance or resistance in the AAF is increased to improve anti-aliasing performance, then the anti-aliasing performance is improved, but the total harmonic distortion increases or the area cost increases
Solution Approach 1:
The patent divides the anti-aliasing filter into two separate signal paths: a main signal path that preserves the original signal with minimal distortion, and a feedforward path that handles anti-aliasing filtering. This segmentation allows each path to be optimized for its specific function without compromising the other.
Solution Approach 2:
The patent extracts the anti-aliasing filtering function from the main signal path and places it in a separate feedforward path. This extraction allows the main signal path to maintain low THD while the feedforward path handles the aggressive filtering needed for anti-aliasing.
2Reliability
If the resistance or impedance of the signal path is increased to improve anti-aliasing, then the anti-aliasing performance is improved, but the total harmonic distortion is impacted
Solution Approach 1:
The patent segments the signal processing into two independent paths, allowing the feedforward path to use high resistance values for effective anti-aliasing filtering without affecting the THD performance of the main signal path.
Solution Approach 2:
The feedforward path acts as an intermediary that processes the input signal separately and subtracts the filtered components from the main signal path, thereby improving anti-aliasing without directly impacting the main signal's THD.
3Reliability
If an active low pass filter comprising a programmable gain amplifier is used to improve anti-aliasing, then the anti-aliasing performance is improved, but the area and power costs increase
Solution Approach 1:
The patent extracts the anti-aliasing function from the main signal path and implements it in a feedforward path that can use passive filtering components, thereby reducing the need for expensive active components like PGAs in the critical signal path.
Solution Approach 2:
The patent uses passive filtering components (resistors and capacitors) in the feedforward path instead of expensive active components, accepting that these components have limitations but are sufficient for their specific anti-aliasing function.
Data Source
AI summary
An analog conditioning circuit and a corresponding method for processing an analog input signal provide a conditioned analog signal for input into an analog processing circuit. The analog conditioning circuit comprises a main signal path between an input for receiving the analog input signal and an output for outputting the conditioned analog signal, wherein the transfer function of the main signal path is constrained by a transfer function requirement associated with the analog processing circuit; and a feedforward signal path comprising a first filtering block configured to attenuate desired frequencies of a first signal derived from the analog input signal to provide a filtered analog signal; wherein the feedforward signal path is configured to input the filtered analog signal into the main signal path such that the filtered analog signal is subtracted from a second signal derived from the analog input signal to provide the conditioned analog signal.