ASK Demodulation Circuit Using Peak-Sampled Mixing
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Solution Overview
Problem
Existing demodulation circuits for ASK coded or amplitude modulated signals face challenges with large dynamic ranges and complex filter designs due to the proximity of carrier and baseband frequencies, leading to inefficiencies and limited operating ranges, especially with small carrier amplitudes.
Innovation Solution
A demodulation circuit that utilizes a sampling mixer with a variable sampling clock adjusted by amplitude maximum detection to ensure sampling at peak amplitudes, combined with signal shaping and delay mechanisms to recover the baseband signal effectively, eliminating carrier frequency components and improving sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a peak detector using a diode is used for rectification, then the demodulation is simple, but the efficiency is bad for small carrier amplitudes which limits the operating range
Solution Approach 1:
The patent replaces the mechanical diode-based peak detector with an electronic switching system using MOSFETs controlled by a sampling clock signal. This electronic substitution allows for much higher efficiency in transferring small carrier amplitudes to the output, extending the operating range from rail-to-rail voltages down to very small amplitude voltages while maintaining demodulation functionality.
Solution Approach 2:
The patent changes the operating parameters of the demodulation system by using a sampling clock signal with frequency equal to or an integer fraction of the carrier frequency. This parameter change enables the switching elements to operate in synchronization with the carrier, achieving high transfer efficiency for small amplitudes without requiring complex filtering or synchronous detection circuits.
2Measurement precision
If synchronous demodulation with a mixer and low pass filter is used, then the demodulation accuracy is improved, but the device complexity and power consumption increase due to need for clock source, mixers and filter
Solution Approach 1:
The patent merges the mixing function and the sampling function into a single stage by using the switching action of MOSFETs controlled by the sampling clock. This eliminates the need for separate mixers, clock sources, and low pass filters that would be required in traditional synchronous demodulation, achieving the same demodulation accuracy with much simpler circuitry.
Solution Approach 2:
The sampling clock signal serves multiple functions simultaneously: it controls the switching of the MOSFETs for signal demodulation, provides the timing reference for accurate sampling at carrier peaks, and eliminates the need for separate mixing and filtering components. This multi-functionality reduces device complexity while maintaining demodulation precision.
3Productivity
If the carrier frequency is close to baseband signal frequencies, then the signal transmission is efficient, but the filter design for suppressing carrier signal becomes complex
Solution Approach 1:
The patent performs preliminary action by sampling the modulated signal at the peaks of the carrier wave before any filtering is needed. By using a sampling clock synchronized to the carrier frequency and switching the MOSFETs at these peak moments, the carrier information is transferred to the output in discrete samples, eliminating the need for complex filters to separate carrier from baseband frequencies.
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 efficient demodulation across a wide range of carrier amplitudes, reduces phase noise requirements, and simplifies filter design by ensuring accurate sampling at amplitude maxima, resulting in higher sensitivity and reliability compared to traditional diode-based peak detection.
Implementation Method 1
a sampling mixer (4) having a sampling signal input (4a) connected to the circuit input (6) to receive the ASK coded or AM signal, a sampling clock input (4b) being adapted to receive a sampling clock signal (SC1) that defines sampling points (SP1) at which the ASK coded or AM signal when being present at the sampling signal input (4a) is sampled
Implementation Method 2
signal delay means (3) being adapted to receive the recovered clock signal and to variably delay the recovered clock signal according to a delay control signal (VDC) at a delay control input (3b) of the signal delay means (3), thereby generating a delayed recovered clock signal (DRC)
Implementation Method 3
amplitude maximum detection means (5) being adapted to detect if the sampling points (SP1) of the sampling mixer (4) correspond to respective amplitude maxima of the signal being sampled and to generate a delay control signal (VDC) being indicative for deviations in time of the sampling points (SP1) from said amplitude maxima
Implementation Method 4
The solution enables efficient demodulation across a wide range of carrier amplitudes, reduces phase noise requirements, and simplifies filter design by ensuring accurate sampling at amplitude maxima, resulting in higher sensitivity and reliability compared to traditional diode-based peak detection
Data Source
AI summary
Conventional modulation envelope demodulators for amplitude modulated signals (e.g. ASK coded signals RX) contain rectifier elements which extract a baseband signal BB. Disadvantageously, due to a non-linear characteristic of the rectifier elements, an amplitude of the baseband signal BB depends on an amplitude of the high-frequent carrier signal. The present invention discloses an improved demodulation circuit for demodulating of ASK coded or amplitude modulated signals. This is achieved by using a sampling mixer 4 and a phase adjusting regulation loop (5) by means of which the sampling of the ASK coded signal RX at its maxima is performed with high accuracy. Due to the absence of any rectifying elements, the baseband signal BB can be fully extracted from the ASK coded signals RX.