Advanced Energy RFG 1251 User Manual page 19

Table 2-1. Block Diagram Explanation
(4) RF Module
(4A) Driver/Exciter
(4B) Power Amplifier
(4C) Output Tank/
Filter
(4D) CEX/Interconnect
5706058-A
The RF module converts dc energy from the inverter to
13.56 MHz and efficiently delivers it to a 50 Ω load. It consists of
four sections mounted on the main cold plate; the driver/exciter
(4A), the power amplifier (4B), the output tank/filter (4C), and
the CEX/interconnect card (4D). The RF module uses a space-
and power-efficient design that is made possible by proprietary
circuitry developed at Advanced Energy Industries, Inc.
The hybrid driver/exciter provides a buffered 13.56 MHz signal
capable of driving the power amplifier (4B). It contains three
stages of amplification. The driver/exciter is designed to drive
extremely low impedance loads and is short circuit protected to
prevent damage due to mishandling or failures in succeeding
stages. It can provide at least twice the power required to drive
the power amplifier to full-rated output power.
The power amplifier (PA) uses the dc power from the inverter (3)
to boost the signal from the driver/exciter (4A) to the required
output level. The power amplifier consist of an AE proprietary,
hybrid module. The efficient operation of this section results in
low heat dissipation which allows a compact arrangement of
components. The PA has a built-in 65% headroom for reliability
when operated into plasma loads. It uses a new class of operation
patented by AE.
This section removes unwanted harmonics generated by the
power amplifier and matches the impedance of the amplifier to a
50 Ω load.
The planar photolithographic techniques used in the output tank
circuitry eliminate air coils and their associated variability due to
operating conditions or manufacturing tolerances. This provides
the RFG with extremely stable operating characteristics.
This section contains the common exciter (CEX) circuitry and
routes the dc and RF drive signals among the various modules
that comprise the RF module. The CEX option provides the
ability to phase lock the outputs of two or more RFG generators
together. In units equipped with this option, a 13.56 MHz signal
of appropriate amplitude applied to the CEX input connector
becomes the reference signal for a phase-locked loop contained
on this card. When no CEX input signal is present (or units
without the CEX option), the crystal oscillator contained on this
card provides the 13.56 MHz reference. The 13.56 MHz signal is
routed to the input of the driver/exciter module (4A).
Theory
RFG 1251 Generator
2-3