AMN50K –
Automatic Impedance Matching Network
Coaxial Power Systems Ltd manufacture an automatic
impedance matching network to link the load to the RF generator. The purpose of
the network is to adjust the input impedance of the load to 50 Ohms so that
maximum power is transferred from the generator, whose output impedance is 50
Ohms, to the load. The network must be installed as close a possible to the
load. The best possible position, in a plasma application for example, would be
to mount the network directly on the vacuum chamber with a direct connection to
the electrode or magnetron.
Manual Matching
Networks
The automatic matching network consists of two
adjustable vacuum capacitors and a fixed inductor, which are usually arranged as
an ”L” network. Other arrangements such as “Pi” and ”T” are also
available. Servo-motors are used to adjust the capacitors for minimum reflected
power as displayed on the generator reflected power meter. When the reflected
power is zero, the system is “tuned” and all of the power output of the
generator is being fed to the load. The inductor and the vacuum capacitors are
water-cooled.
At the
input of the network, a phase and magnitude detector determines the position of
the capacitors. This information is transferred to the separate controller. The
controller then drives the servomotors to the positions, which give zero, or
minimum reflected power.
The controller is ½ rack, 4U high and is usually
fitted in the same enclosure as the generator. The position of each variable
capacitor is shown on a 31/2 digit LED meter. Automatic or Manual mode is switch
selectable - in manual mode the servomotors are controlled by spring loaded
switches. The start position of the capacitors can be individually adjusted.
When RF power is detected, the capacitors automatically adjust for minimum
reflected power. When the RF is turned off, the motors drive the capacitors back
to heir original position. The start positions are adjusted using potentiometers
accessible via the controller front panel
Option: Model
DCP-1 : Dark Space Bias Voltage Measurement and Control
A
probe, installed inside the network, measures the d.c voltage (0 to 5000V)
developed across the dark space in plasma applications such as sputtering and
reactive ion etching. The voltage is converted to a 0 to 5V signal which can be
fed back to the generator control system. The voltage is displayed on the
loading capacitor position meter. Includes all necessary cables to link to any
generator in the low power range manufactured by Coaxial Power Systems Ltd.
(07.06.2007)