Tri-State Chopper Frequency Conversion for Harmonic Rejection
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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, causing spurious mixing products, especially in TV tuners that need to select channels within a wide frequency range.
Innovation Solution
A tri-state chopper (TSC) circuit is used for frequency conversion, employing a ternary control signal with three states to generate output signals that track the input signal in magnitude and sign, invert the input signal, or set the output to zero, allowing for selective harmonic rejection by manipulating the relative strengths of harmonics through multi-level transmit, 3-level (MLT-3) waveforms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional mixers are used for frequency conversion, then frequency conversion can be performed, but harmonic mixing occurs causing spurious mixing products
Solution Approach 1:
The patent divides the frequency conversion function into multiple parallel TSC circuits (first TSC circuit and second TSC circuit) that process different aspects of the signal. Each TSC circuit handles specific harmonic suppression while working together to achieve complete spurious-free conversion, segmenting the harmful harmonic mixing effect across multiple processing paths.
Solution Approach 2:
The patent introduces an intermediary MLT-3 waveform signal as a control signal for the TSC circuits. This intermediary signal acts as a mediator between the input RF signal and the output, enabling the TSC circuits to perform frequency conversion while suppressing harmonics through the specific 3-level waveform characteristics.
2Speed
If direct conversion architecture is used, then conversion speed is improved, but harmonic mixing cannot be avoided
Solution Approach 1:
The patent employs periodic MLT-3 waveforms as control signals for the TSC circuits. These periodic 3-level waveforms enable the circuits to perform rapid switching operations at the desired conversion speed while the periodic nature ensures consistent harmonic suppression across all conversion cycles, maintaining both speed and purity.
Solution Approach 2:
The patent changes the control signal parameter from traditional binary (2-level) to ternary (3-level) MLT-3 waveforms. This parameter change enables the TSC circuits to achieve both fast conversion speed and harmonic suppression, as the additional signal level provides better control over the switching behavior and harmonic content.
3Object-generated harmful factors
If multiple TSC circuits are used to suppress harmonics, then spurious-free conversion is achieved, but device complexity increases
Solution Approach 1:
The patent merges the functionality of multiple TSC circuits by having them work in parallel with complementary functions. The first and second TSC circuits are combined such that their outputs are summed, achieving complete harmonic suppression while the merged structure is more efficient than separate independent circuits would be.
Solution Approach 2:
The TSC circuits are designed with multi-functionality, serving both as frequency converters and as harmonic suppressors simultaneously. This universal design eliminates the need for separate harmonic filtering stages, reducing overall device complexity despite using multiple TSC circuits.
Data Source
AI summary
A method of performing frequency conversion and associated frequency converter are provided. The method includes: receiving an input signal and a plurality of periodic ternary signals of the same frequency but different timings; generating a plurality of conversion signals using a plurality of conversion paths in response to the input signal and states of said periodic ternary signals; and summing the conversion signals to generate an output signal.