Sub-Harmonic Mixer Resonance Circuit for DC Offset Reduction
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Solution Overview
Problem
Direct-conversion receivers face challenges with DC offset and even-order distortion due to unsymmetrical circuit mismatching in conventional sub-harmonic mixers, leading to leakage signal and distortion issues.
Innovation Solution
A sub-harmonic mixer is designed with a differential amplifying unit and a current buffer unit, utilizing first and second resonance circuits to orient leakage signals to specific voltages, enhancing isolation and reducing DC offset and even-order distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional sub-harmonic mixer is used, then isolation between input terminals is improved, but DC offset and even-order distortion are generated due to unsymmetrical circuit mismatching
Solution Approach 1:
The patent applies asymmetry by intentionally introducing asymmetrical elements (resistors R1-R4 with different values, capacitors C1-C4 with different values) into the symmetrical differential amplifier circuit. These asymmetrical components compensate for the unsymmetrical mismatching in the transistors, thereby reducing even-order distortion and DC offset while maintaining good isolation between input terminals.
Solution Approach 2:
The patent changes the parameters of passive components (resistors and capacitors) to optimize circuit performance. By carefully selecting different resistance and capacitance values for various components, the circuit achieves better balance and reduced distortion while maintaining isolation properties.
2Productivity
If poly-phase LO signal frequency is reduced to 0.5 times RF signal frequency, then sub-harmonic mixing is achieved, but leakage signal and even-order distortion increase due to circuit mismatching
Solution Approach 1:
The patent applies local quality by making different parts of the circuit have different characteristics. Specifically, different transistors have different width-length ratios, and different passive components have different values, allowing each part to compensate for local mismatching effects and reduce overall distortion.
Solution Approach 2:
The patent introduces asymmetrical passive components (resistors and capacitors with different values) into the differential amplifier to counterbalance the asymmetrical mismatching that occurs when using sub-harmonic LO frequency, thereby reducing leakage and distortion.
3Device complexity
If simple direct-conversion receiver structure is used, then device complexity is reduced, but isolation between input terminals deteriorates leading to DC offset
Solution Approach 1:
The patent changes the parameters of passive components in the differential amplifier stage to optimize isolation performance. By selecting specific resistance and capacitance values, the circuit achieves better input terminal isolation without adding complex external filtering components.
Solution Approach 2:
The patent introduces passive components (resistors and capacitors) as intermediary elements that mediate between the mismatched transistors. These intermediary components help balance the circuit and improve isolation without fundamentally changing the simple direct-conversion receiver architecture.
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 improved isolation significantly reduces DC offset and even-order distortion, enhancing the performance of direct-conversion receivers by effectively managing leakage signals and distortion.
Implementation Method 1
utilizing first and second resonance circuits to orient leakage signals to specific voltages
Implementation Method 2
mixing a poly-phase local oscillation (LO) signal and a radio frequency (RF) signal so as to produce a base band signal
Data Source
AI summary
A sub-harmonic mixer and a down converter with the sub-harmonic mixer are provided. The sub-harmonic mixer includes a differential amplifying unit, a current buffer unit, and a switching unit. The differential amplifying unit is used to amplify a radio frequency (RF) signal and employs a first resonance circuit to force a leakage signal to flow to a first voltage. The current buffer unit is used to amplify the gain of an output signal of the differential amplifying unit and employs a second resonance circuit to force the leakage signal to flow to a second voltage. Finally, the switching unit switches an output signal of the current buffer unit into a base band signal.