Synchronous Demodulation Using Passive Sampled Analog Filters
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Solution Overview
Problem
Existing analog continuous time filters used in signal processing are difficult to control coherently, especially when implementing bandpass filtering, leading to unpredictable phase responses and challenges in achieving coherent processing, particularly due to their IIR nature and sensitivity to center frequency changes.
Innovation Solution
The implementation of passive sampled analog filtering systems that use a combination of passive sampled analog filters and mixers to perform synchronous demodulation, allowing for coherent signal processing with reduced phase errors and improved control over center frequencies, utilizing programmable or fixed filters such as FIR and IIR filters, and amplifiers to enhance signal amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog continuous time filters using opamps are used for bandpass filtering, then filtering function is achieved, but phase control becomes difficult and unpredictable phase errors occur
Solution Approach 1:
The patent replaces traditional analog continuous time filters using opamps with a discrete-time filter implementation. This substitution eliminates the unpredictable phase responses and center frequency drifts inherent in analog filters, providing precise digital control over filter characteristics including phase response, while maintaining the bandpass filtering function.
Solution Approach 2:
The patent transforms the filter from continuous-time analog domain to discrete-time domain, changing fundamental parameters such as time continuity and control methodology. This allows precise control of filter parameters (center frequency, bandwidth, phase response) through digital programming rather than analog component tuning, resolving the phase control precision issue.
2Reliability
If modulation frequency is set to exactly fc, then frequency matching is achieved, but unpredictable phase response of filter still prevents coherent processing
Solution Approach 1:
The patent replaces the analog filter with a discrete-time filter that provides predictable and controllable phase response. This substitution ensures that when the modulation frequency is set to fc, the system achieves both frequency matching and reliable coherent processing, as the digital filter's phase response can be precisely controlled and predicted through software.
Solution Approach 2:
The patent implements a feedback mechanism where the system measures the actual phase response and adjusts the processing accordingly. This feedback loop compensates for any residual phase variations and ensures coherent processing reliability, allowing the system to maintain synchronization even with frequency variations.
3Measurement precision
If high ADC sampling rates are used, then signal processing accuracy is improved, but power consumption increases
Solution Approach 1:
The patent applies partial action by using oversampling at a moderate rate followed by digital decimation. Instead of continuously processing at the highest possible sampling rate, the system samples at a rate slightly above the minimum required, then uses digital filtering to achieve the desired signal processing accuracy. This approach maintains measurement precision while significantly reducing power consumption compared to continuous high-rate sampling.
Solution Approach 2:
The patent implements periodic processing where signals are sampled, filtered, and processed in discrete batches or frames rather than continuously at high rates. This periodic action allows the system to achieve accurate signal processing when needed while entering lower-power states between processing intervals, reducing overall power consumption.
Data Source
AI summary
Systems and methods for synchronous demodulation using passive sampled analog filtering are disclosed. A system for synchronous demodulation includes an input channel for accepting an input signal, a first passive sampled analog filter for filtering the input signal, a mixer for mixing the filtered input signal and outputting a mixed signal, a second passive sampled analog filter for filtering the mixed signal, and an output channel for outputting the filtered mixed signal.