Sampling Mixer With Stepped Phase Modulation for Image-Free Frequency Shift
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Solution Overview
Problem
Conventional mixer technology relies on nonlinear semiconductor junction devices, leading to limitations such as the generation of unwanted 'image frequencies' and finite attenuation of undesired signal terms, which complicates frequency conversion and signal modulation.
Innovation Solution
A frequency conversion circuit utilizing stepped phase modulation to shift the frequency of an input signal, avoiding the non-linear behavior of semiconductor devices and achieving uni-directional frequency shifts by imposing a series of phase-modulation steps on the input signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional mixer technology uses nonlinear semiconductor junction devices for frequency conversion, then frequency translation can be achieved, but image frequencies are generated and undesired signal terms are not fully attenuated
Solution Approach 1:
The patent extracts and removes the problematic nonlinear semiconductor junction device from the frequency conversion process. Instead of using a diode-based mixer that generates image frequencies, the invention uses a sampling switch that directly samples the RF signal at LO frequency intervals, eliminating the generation of image frequencies while achieving the desired frequency translation to IF.
Solution Approach 2:
The patent replaces the conventional electronic nonlinear mixing mechanism with a sampling-based approach using a controlled switch. The sampling switch opens and closes at LO frequency intervals, creating impulses that translate the RF signal to IF through sampling in the time domain, substituting the nonlinear junction behavior with a linear sampling operation.
2Reliability
If conventional mixers use filtering to attenuate undesired terms, then some signal purification is achieved, but finite attenuation leaves residual unwanted signals
Solution Approach 1:
The patent extracts the frequency selection function from the filtering stage and moves it to the sampling stage. By sampling the RF signal at specific LO frequency intervals, the desired IF signal is directly generated while unwanted frequencies are naturally rejected, eliminating the need for complex filtering to achieve signal purification.
Solution Approach 2:
The patent performs frequency selection preliminarily through the sampling operation before any filtering is needed. The sampling process itself acts as a frequency selector, creating impulses at the desired IF frequency while rejecting other frequencies, so that subsequent filtering only needs to perform simple cleanup rather than complex attenuation of image frequencies.
3Adaptability or versatility
If two different RF input frequencies are used in conventional mixers, then both can be converted to the same output frequency, but this creates ambiguity in frequency conversion
Solution Approach 1:
The patent replaces the symmetric nonlinear mixing process with an asymmetric sampling process. The sampling switch creates a one-to-one mapping between RF input frequency and IF output frequency through the sampling theorem, eliminating the two-to-one mapping ambiguity of conventional mixers while maintaining frequency conversion flexibility.
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
This approach effectively eliminates 'image frequencies' and provides a precise, uni-directional frequency shift, improving the accuracy and efficiency of frequency conversion compared to conventional methods.
Implementation Method 1
A sampling mixer or s-mixer produces a frequency shift in an input RF signal through the imposition of a series of phase-modulation steps on the input signal. A sampling switch samples the RF signal at intervals determined by the LO signal frequency to produce a train of impulses.
Implementation Method 2
A sequence generator produces a sequence of control signals that control the phase of the LO signal in a stepped fashion to approximate a phase ramp. The phase shifter device imparts a phase shift on the LO signal based on the control signals from the sequence generator.
Implementation Method 3
A phase shifter device imparts a phase shift on the LO signal based on the control signals from the sequence generator. The combination of the phase shifter device and sampling switch produces a frequency shifted version of the RF signal.
Data Source
AI summary
A unidirectional sampling mixer utilizes a stepped phase modulation to shift the frequency of an input signal. An RF input signal is supplied to an RF input switch from an RF input port. An ordered set of phase shift values to be applied to the RF input signal and a set of times each element of which correspond to a time at which a phase shift value is be applied to the RF signal are determined. For each phase shift value within the ordered set of phase shift values, a controller controls the RF input switch to select an input of a phase shifting device and controls an RF output switch to select an output of the phasing shifting device. The input of the phase shifting device and the output of the phase shifting device are selected to apply the phase shift value at its corresponding time to the RF input signal. A frequency shifted signal is supplied to an RF output port from an output of the RF output switch. This Abstract is not to be considered limiting, since other embodiments may deviate from the features described in this Abstract.