Multi-stage heterodyne control circuit for pulsed RF power
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Solution Overview
Problem
Single-stage heterodyne control circuits are inadequate for accurately monitoring and controlling pulsed RF power in semiconductor fabrication processes due to limitations in hold capacitor charging speed, leading to errors in power detection and output control.
Innovation Solution
A multi-stage heterodyne control circuit with a first heterodyne stage for down-converting input signals using a low pass filter and a second heterodyne stage for up-converting filtered signals using a band pass filter, followed by a detection stage to generate a DC signal for precise power control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-stage heterodyne control circuit is used, then the device complexity is low, but the measurement precision of pulsed RF power deteriorates due to hold capacitor charging speed limitations
Solution Approach 1:
The patent divides the single-stage heterodyne control circuit into multiple stages: a first heterodyne stage for down-converting the RF signal to an intermediate frequency, and a second heterodyne stage for further processing. This segmentation allows each stage to use appropriately sized hold capacitors that can charge discharge quickly enough to accurately measure pulsed RF power while maintaining manageable device complexity through modular design
Solution Approach 2:
The patent introduces an intermediate frequency dimension between the original RF signal and the baseband signal. By down-converting to an intermediate frequency in the first heterodyne stage, the system creates a new frequency dimension that allows for more flexible capacitor sizing and faster charging/discharging cycles, thereby improving measurement precision without excessively increasing device complexity
2Device complexity
If a hold capacitor is used in the detection circuit, then the circuit structure is simple, but the measurement precision deteriorates because the capacitor cannot charge fast enough to capture peak values of MHz-range pulsed signals
Solution Approach 1:
The detection function is segmented across two heterodyne stages, each with its own hold capacitor. The first stage processes the signal at a higher frequency with a smaller capacitor capable of faster charging, while the second stage handles the intermediate frequency with another capacitor optimized for that frequency. This segmentation enables accurate peak detection of MHz-range pulses while keeping individual capacitor values and circuit complexity manageable
Solution Approach 2:
The patent changes the frequency parameter of the signal through heterodyne down-conversion, transforming the MHz-range pulsed signal into a lower intermediate frequency signal. This parameter change allows the hold capacitor to charge and discharge within the pulse duration, enabling accurate peak value detection that would be impossible at the original higher frequency
3Measurement precision
If the hold capacitor value is increased to improve measurement accuracy, then the measurement precision improves, but the charging speed decreases making it impossible to track fast pulsed signals
Solution Approach 1:
The measurement function is segmented into two heterodyne stages, each with its own hold capacitor optimized for different frequency ranges. The first stage uses a smaller capacitor optimized for the higher RF frequency, while the second stage uses a capacitor optimized for the lower intermediate frequency. This segmentation allows each capacitor to be sized appropriately for its specific frequency, achieving both fast charging speed and accurate measurement without the trade-off present in a single-stage design
Solution Approach 2:
The patent changes the frequency parameter of the signal through heterodyne down-conversion, which allows the system to use a smaller hold capacitor in the first stage that can charge fast enough to track MHz-range pulses. The parameter change from high frequency to intermediate frequency enables the capacitor to respond quickly to pulse peaks while still achieving accurate power measurement
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 multi-stage heterodyne control circuit enables accurate measurement and control of pulsed RF signals, reducing errors and improving power detection accuracy by utilizing smaller hold capacitors with faster charge times, thus effectively managing the challenges of pulsed RF power in semiconductor fabrication.
Implementation Method 1
a first heterodyne stage receiving an input signal, the input signal being based on a characteristic of an RF signal generated by the RF generator, with the first heterodyne stage configured to: mix the input signal with a first mix signal to generate a first heterodyne signal
Implementation Method 2
filter the first heterodyne signal through a low pass filter
Implementation Method 3
a second heterodyne stage receiving the filtered first heterodyne signal, the second heterodyne stage configured to: mix the filtered first heterodyne signal with a second mix signal to generate a second heterodyne signal
Implementation Method 4
filter the second heterodyne signal through a band pass filter
Implementation Method 5
a detection stage configured to convert the filtered second heterodyne signal to a DC signal
Data Source
AI summary
A circuit for controlling an RF generator, the circuit including first and second heterodyne stages. The first heterodyne stage receives an input signal, which is based on a characteristic of an RF signal generated by the RF generator, and is configured to: mix the input signal with a first mix signal to generate a first heterodyne signal and to filter the first heterodyne signal through a low pass filter. The second heterodyne stage receives the filtered first heterodyne signal and is configured to: mix the filtered first heterodyne signal with a second mix signal to generate a second heterodyne signal and to filter the second heterodyne signal through a band pass filter. A detection stage converts the filtered second heterodyne signal to a DC signal, and a power control stage receives the DC signal and controls the RF signal in response to the DC signal.