Tri-State Chopper Frequency Conversion for 3K Harmonic Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Direct conversion receivers face challenges in frequency conversion due to harmonic mixing, where undesired signals are converted along with the desired signal due to mixing with odd-order harmonics of the local oscillator, making it difficult to select specific channels without spurious mixing products.
Innovation Solution
A tri-state chopper (TSC) circuit is employed, which uses a ternary control signal to generate an output signal that tracks the input signal in magnitude and sign in certain states, has an opposite sign in another state, and is set to zero in a third state, allowing for flexible manipulation of harmonic suppression by using multiple parallel TSC circuits and summing their outputs to reject specific harmonics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct conversion architecture is used with traditional mixers, then frequency conversion is achieved, but harmonic mixing causes spurious signals and undesired channels to be converted along with the desired signal
Solution Approach 1:
The patent divides the frequency conversion function into multiple parallel TSC circuits, each handling different frequency components. By segmenting the conversion process across multiple circuits with different control signal frequencies, the system can selectively convert desired channels while rejecting harmonics through destructive interference of spurious products.
Solution Approach 2:
The patent changes the control signal frequency parameter of TSC circuits to achieve harmonic suppression. By operating TSC circuits at control frequencies that are not integer multiples of each other, the system shifts harmonic products to different frequencies where they can be filtered out, thereby improving signal purity while maintaining conversion functionality.
2Ease of operation
If traditional mixers are used for frequency conversion, then channel selection is possible, but odd-order harmonics of the local oscillator cause undesired signals to be converted
Solution Approach 1:
The patent segments the channel selection process across multiple TSC circuits, each tuned to different control frequencies. This segmentation allows the system to maintain channel selection capability while distributing the conversion function to prevent any single mixer from generating strong harmonic products that would interfere with desired channels.
Solution Approach 2:
The patent converts the harmful effect of harmonics into a beneficial filtering mechanism. By intentionally allowing harmonics to be generated but designing the control frequencies such that harmonic products fall into stopband regions, the system uses the presence of harmonics to define passband and stopband characteristics, thereby improving channel selectivity.
3Reliability
If multiple parallel TSC circuits are used for harmonic suppression, then spurious-free signals are achieved, but device complexity increases
Solution Approach 1:
The patent merges multiple TSC circuits into a unified frequency conversion system where the circuits operate in parallel but share common input and output stages. By combining the outputs of multiple TSC circuits through proper phasing and amplitude balancing, the system achieves harmonic suppression equivalent to having a single complex mixer, thereby reducing overall system complexity while maintaining reliability.
Data Source
AI summary
A tri-state chopper (TSC) circuit and method is disclosed. The tri-state chopper (TSC) circuit receives an input signal and a ternary signal and generates an output signal, wherein: the output signal tracks the input signal in both magnitude and sign when the ternary signal is in a first state; the output signal tracks the input signal in magnitude but has an opposite sign when the ternary signal is in a second state; and the output signal is set to zero when the ternary signal is in a third state.