AC-Coupled Doppler Radar Mixer for Diode Matching Flexibility
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing Doppler radar mixer structures face challenges in achieving optimal signal amplitude and impedance matching, leading to signal loss due to high IF output impedance and the need for precise diode matching, which is difficult and inflexible, especially in low-cost applications.
Innovation Solution
The mixer structure incorporates rectifier circuits with diodes, load resistors, decoupling capacitors, and series resistors and capacitances, connected via hybrid couplers, allowing for separate optimization of mixer branches and impedance matching, enabling higher intermediate voltage signals and improved noise rejection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diodes are connected in direct current (DC) in known art mixer structures, then the current flowing between the diodes provides inherent low radio frequency impedances, but this makes impedance determination and diode matching difficult and inflexible
Solution Approach 1:
The patent segments the DC connection by introducing AC coupling capacitors that separate the DC bias paths of the two diodes while allowing AC signal mixing. This segmentation enables independent diode biasing and matching, eliminating the need for precise diode matching while maintaining noise cancellation through the AC signal path.
Solution Approach 2:
The patent introduces AC coupling capacitors as intermediary elements between the diodes and the output circuit. These capacitors block DC current while passing AC signals, thereby decoupling the DC bias requirements of the diodes from the AC signal mixing function, which simplifies diode matching and selection.
2Manufacturing precision
If a mixer structure with low IF output impedance is used, then radio frequency amplifiers with 50 Ohms impedance can be matched, but signal loss occurs due to mismatch with high impedance operational amplifiers
Solution Approach 1:
The patent changes the impedance parameter of the mixer output by transforming it from a low impedance (50 Ohms) to a high impedance configuration. This is achieved through the AC coupled diode configuration and output circuit design, which presents a high impedance to the operational amplifier, thereby matching the high input impedance of AF amplifiers and eliminating signal loss.
3Ease of manufacture
If simple low cost operational amplifiers are used for IF signal amplification, then cost is reduced, but signal amplitude is lost due to high input impedance mismatch with low impedance mixer structures
Solution Approach 1:
The patent changes the impedance parameter of the mixer output to high impedance, which matches the high input impedance of simple low-cost operational amplifiers. This parameter change eliminates the impedance mismatch that would otherwise cause signal amplitude loss, allowing the use of inexpensive AF amplifiers without sacrificing signal strength.
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 configuration enhances signal amplitude and flexibility in diode selection, reduces signal loss, and allows for easier and more reproducible measurements, while maintaining effective noise cancellation and impedance matching, resulting in a more efficient and cost-effective Doppler radar sensor.
Implementation Method 1
two mixer branches 12a, 12b each with a diode 18a, 18b... intermediate signals, which are produced in these mixer branches and correspond to a Doppler shift
Data Source
AI summary
A Mixer structure (210) for Doppler radar applications and a Doppler radar sensor (30) having an oscillator input port (LO) for output signals from an electric oscillator (32), having an radio frequency input port (RF) for output signals from receiving means (34), having an output port (IF) for an overall output intermediate signal produced in the mixer structure (210) and having two mixer branches (12a, 12b) each with a diode (18a, 18b). The mixer branches (12a, 12b) are connected to the oscillator input port (LO) and to the radio frequency input port (RF) in such a manner that intermediate signals (IF1, IF2), which are produced in these mixer branches (12a, 12b) and correspond to a Doppler shift between the oscillator signal and the radio frequency signal, are processed to the overall output signal.