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System and Method of Controlling RF Power Generator

IP.com Disclosure Number: IPCOM000235545D
Publication Date: 2014-Mar-07

Publishing Venue

The IP.com Prior Art Database

Abstract

A system and method of controlling an RF power generator comprises a power generator, a sense module, an adjustment module and a controller. The sensor module senses a forward power feedback signal and a load reflection coefficient. The adjustment module estimates the true forward power value based on the working frequency of the RF power generator, the load reflection coefficient, and an external setpoint signal and adjusts the external setpoint signal based on the true forward power value to obtain an adjusted setpoint signal. The controller controls the RF power generator system based on the adjusted setpoint signal, as well as the forward power feedback signal.

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SYSTEM AND METHOD OF CONTROLLING RF POWER GENERATOR

FIELD

[0001]         The present disclosure relates to controllers for radio frequency (RF) power generators, and more particularly to controllers that accurately regulate power under mismatched load conditions. 

BACKGROUND

[0002]         Many radio frequency (RF) power generators include  control systems that regulate RF output power into mismatched loads and prevent amplifier damage  from excessive supply voltage, current, and excessive operating temperature.  Certain RF generator applications require extremely accurate and repeatable power delivery into mismatched loads (loads with complex reflection coefficient > 0).  For example, an RF plasma thin film processing system utilizing a fixed matching network and variable frequency RF generator will routinely place loads with reflection coefficient of 0.2 or greater at the generator output.  Under these conditions, the directional couplers used to sense the RF power will exhibit significant uncertainty leading to process repeatability problems.  FIG. 1 shows a typical radio frequency (RF) power generator 10 that includes a power module 11 and a controller 12.  The power module 11 receives signals from RF exciter 14, amplifies the signals, and delivers the signals to a load 16.  The power module 11 includes a driver 18 and a final amplifier 20.  The power module 11 receives DC power through a cable 24 that is coupled to a DC power supply 26 . The cable 24 may have substantial distributed impedance.  The controller 12 includes an amplifier 30, a frequency compensation capacitor 34, and a buffer 38.  The controller 12 receives control inputs 40 and feedback signals 42 and produces a control voltage 44 that varies the gain of the driver 18.

[0003]         The controller 12 precisely regulates output power during normal conditions and protects the power module 11 during abnormal conditions.  The controller 12 employs negative feedback to diminish an error between the greatest feedback signal and a reference input that has been selected according to nominal operating levels of the feedback transducers.  Feedback signals from the directional coupler 60 include forward and reverse power signals 50 and 52 that are generated by RF detectors 54 and 56.  The detectors 54 and 56 are typically coupled to sampling arms of a directional coupler 60, but could also be implemented with a voltage and current sensor (also known as a VI probe).  The finite directivity of the coupler (typically 20-30dB) will lead to measurement errors when the reflection coefficient is non-zero.  The power regulation system can operate in forward power leveling mode, or load power (forward minus reflected power) leveling mode.  Other feedback signals include a temperature signal 62 from a thermistor 64 that is thermally coupled to the final amplifier 20.  Differential voltage feedback signals 66 and 70 are proportional to DC input current to the power module 11 (through a current-sampl...