3-2
variable pulse width signal (RFGATE). This
amplifier is combined through a relay with either
the Monopolar output transformer or the Bipolar
output transformer to generate electrosurgical
power.
Electrosurgical power flows from the RF
Amplifier / Transformer section to the Output sec-
tion where the power is switched to the specific
electrosurgical outputs. The Output section also
has circuitry to detect activations from accessories
and the circuitry to perform the Automatic Return
Monitor (A.R.M.) function to ensure the integrity
of the dispersive electrode connection.
The power section also includes a number of out-
put voltage and current sensors that are used by
the RF Controller for control of power delivery
and by the Monitor to detect errant output condi-
tions. Windings on the Monopolar output trans-
former and the Bipolar output transformer are the
means for sensing output voltage. Separate pri-
mary-side current transformers are shared by the
bipolar and monopolar channels for control and
monitoring of the current. There are also separate
current sensors on the monopolar outputs that are
used to detect stuck output relays.
The RF Controller is a Field Programmable Gate
Array (FPGA) that generates the RFGATE and
VBASE_PWM RF Amplifier drive signals based
upon a comparison of measured parameters
and settings-based parameters. The pulse train
sequence is a settings-based parameter that is
dependent on the selected mode. Target power,
current limit, and voltage limit are all settings-
based parameters derived from a load curve that
is specific to the selected mode and front panel
power setting. The RF Controller samples
electrosurgical output current and output volt-
age from sensors at a 20 Megahertz rate and uses
these sampled values to calculate sensed current,
sensed voltage, and output power. This high sam-
ple rate allows control of the real power delivered
to the active accessory and also allows the System
2450 to rapidly adapt to changing loads. The
output current, output voltage, and output power
are compared with corresponding settings based
parameters of current limit, voltage limit, and
target power, respectively, and the RF Controller
adjusts value of VBASE_PWM in a closed-loop
fashion to control these parameters. The RF
Controller also provides fixed pulses for RFGATE
within each mode-based pulse train sequence.
The RF Monitor is a Digital Signal Processor
(DSP) that is used to monitor the system for
safety problems that can result from a variety of
conditions.
• The Monitor has independent sensors for out-
put voltage and current, which it uses to cal-
culate power for comparison with the power
that the RF Controller senses and for com-
parison with the generator power setting.
• To ensure that the correct outputs are acti-
vated, the Monitor also independently
senses current at each of the outputs, look-
ing for current flow that would indicate
electrosurgical power at outputs other than
the selected output.
• The Monitor senses the audio output to ensure
that a tone occurs whenever electrosurgical
outputs are active.
• The RF Amplifier drive signal is sensed by
the Monitor to detect improper frequencies
or improper pulse sequences for the selected
mode.
• The Monitor independently compares the
activation signal with that seen by the System
Controller to ensure that the activation signal
is consistent.
The Monitor has the capability to independently
disable the electrosurgical output if a problem is
detected.
The System Controller provides the primary con-
trol interface to the user and other outside sys-
tems, including the serial interface, the activation
relay, tone generation, and displays.
Finally, the Display accepts all user input and pro-
vides all user feedback. The Display is controlled
by the System Controller through a serial interface
and illuminates the LED display elements in a
time division multiplexed fashion; the illuminated
LED display elements are actually on less than half
the time. The Display also provides for user input
through the buttons on the control panel, includ-
ing switch de-bouncing and conditioning.
Figure 3.2 illustrates the key elements of the sys-
tem in block diagram form.
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