els) of the input signal from the pacer module. IC110 buffers
the signal, which is fed to J109 via R129.
5. Internal Power Supply Sensor Board (Schematic Diagram 5).
IC107 regulates the -9 volt potential down to stable -5V for use
in the A/D converter system. Dl14 prevents incorrect polariza-
tion and latch-up when the QA-45 is switched on and off. D108,
D109 and Dl10 provide over-voltage protection.
6. Measurement Input (Schematic Diagram 6).
R185 and R186 together make up a 50-ohm load resistance for
the discharges from the defibrillator being tested. The voltage
over the resistors is conducted via IC101 and IC102 into the A/
D converter IC104. This samples the voltage every 100 µs, and
the measurement values are transferred digitally to the micro-
processor.
The measurement input is based on an attenuator that consists
primarily of a differentially connected operational amplifier
(IC101). Using SW109, the attenuation can be set as 10, 200 or
1000 times. The output signal from IC101 may fluctuate from
+5 to -5 Volt. With an input attenuation of 1000, the measure-
ment range becomes +5000 to -5000 Volt (High Range). With
an input attenuation of 200, the measurement range becomes
+1000 to -1000 Volt (Low Range). With an input attenuation of
10, the measurement range becomes +50 to -50V (pacer mode).
IC102 is used as an addition amplifier. Here, the measurement
signal is added to an offset signal generated by the other half of
IC102, set using P103. A test signal can also be added in to test
the A/D converter function. P102 adjusts the input attenuation.
7. A/D Converter (Schematic Diagram 6). The A/D converter sys-
tem consists of IC104, IC105 and, IC106. IC104 is the A/D con-
verter itself, while IC105 is the voltage reference, and IC106 is
the clock generator.
The analogue signal is fed into the A/D converter on pin 7, and
the measurement result is read serially on pins 15 to 18. The A/
D has a differential input, and can function with 12- or 13-bit
resolution. IC106 is a square wave oscillator that generates the
clock signal to the analogue part of the A/D converter. The fre-
quency of the signal is nominally 1.9 MHz, but may vary be-
tween 1.7 and 2.1 MHz.
IC105 is the voltage reference for the A/D converter. P104 can
be used for precise adjustment of the voltage to exactly 5 Volt
(TPl12).
7.4 ECG Signal Distribu-
tion Board
(Refer to QA-45 ECG Distribution Board Component Location Dia-
gram and Schematic Diagram 7)
4
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