
modules to set up the amplifier, the high-pass
filter and to switch in the d.c. offset as required.
The analogue patient signals from the electrode
board are low-pass filtered on this board and then
multiplexed to both halves of the dual ADC,
which digitises and serialises the signals under
control of the PAL. The serialised data stream is
returned to the mainframe along with a clock and
strobe (frame) signal from the PAL, to be
processed by the DSP.
When D.C. Mode is selected, the PIC can remove
the input offset. The first four amplifier channels
are also input directly to four inputs on the PIC
which are configured as ADC’s. The PIC then
outputs a serial stream of data to control the d.c.
offset that is applied to the amplifier inputs. This
is requested by the operator under software
control.
A fifth input on the PIC is also configured as an
ADC to monitor the analogue signal from the
temperature probe.
4.6.2
The Electrode Board
There are 18 (+2 Neutral) EP electrode inputs and
2 (+ Neutral) EMG Channel inputs for the headbox
that are input via this board.
All inputs are routed to cross-point switches which
determine which input is connected to which
amplifier module as selected by the operator. The
cross-point switches also route the common mode
reference signals back from the amplifier modules
to the screen driver for the EP Channel inputs. The
reference signals from the EMG input amplifiers
are routed directly to the EMG screen driver pins
on the DIN socket.
The cross-point switches are powered from a
+- 10V supply bootstraped by the common mode
reference signal and derived from the isolated
+-15V supply to compensate for capacitive loading
of the signals within the switches.
The first four channels can be software configured
to have a d.c. offset applied to their input stages
which is derived from a quad channel serial DAC
driven from the PIC on the Control Board. This is
used to remove any offset up to
±
500mV present
in the input signal.
Issue A May 1998
TECHNICAL OVERVIEW
Chapter 4 Page 10
Synergy Mobile Workshop Manual
LOW PASS
FILTERS
LOW PASS
FILTERS
MULTIPLEXER
MULTIPLEXER
DUAL
ADC
MICROCONTROLLER
CH2,4
CH1,3
CLK LINES
DATA LINE
STROBE LINES
PAL
CRYSTAL
COUNTER
16MHz
CONV
XC
L
K
A0-A2
CH1,3,5
CH2,4
CAL
FROM ROTARY SWITCHES
AND PUSH-BUTTONS
TEMPERATURE PROBE
OPTO
ISOLATOR
OPTO
ISOLATOR
OPTO
ISOLATOR
OPTO
ISOLATOR
OPTO
ISOLATOR
OPTO
ISOLATOR
DUAL
RS232
RX
TX
DIFFERENTIAL
BU
S
TRANSCEIVER
FRAME
CLOCK
DATA
SYNC
ISOLATING
TRANSFORMER
SWITCHING
REGULATOR
AND DRIVER
+12V
ISOLATED
D.C. SUPPLIES
IS
OLA
T
ION
BARR
IER
RECTIFIER AND
+5V REGULATOR
+5V
-12V
Figure 3- Schematic diagram of the 5 Channel headbox Control Board