Datasheet

Thursday, 17 July 2003 MiniProject: Design Aspects Colin K McCord
EEE512J2 – Electronic Product Design Page 5 Chapter 2: Fundamentals
than about 50 hertz. A 3 lead cable connects the circuit to the electrodes and two wires are required to
connect the output to an ADC for sampling.
4.7k 47k
1uF 1uF
Simple Low Pass Filter
To ADC
47k
47k
10M
10k
1
2
3
11
13
12
16
AD624AD
8
4
5
6
7
9
10
+9V
-9V
1uF
1uF
Electrode 1
Electrode 2
Electrode 3
Figure 2.3a. Simple ECG Amplifier
2.4. The Cathode Ray Tube (CRT)
“The CRT is a glass bulb which has had the air removed and then been sealed with a vacuum inside. At the
front is a flat glass screen which is coated inside with a phosphor material. This phosphor will glow when
struck by the fast moving electronics and produce light, emitted from the front and forming the spot and
hence the trace. The rear of the CRT contains the electron ‘gun’ assembly. A small heater element is
contained within a cylinder of metal called the cathode. When the heater is activated by applying a voltage
across it, the cathode temperature rises and it then emits a stream of electrons.” [B2].
-2000V -1500V +100V +100V +100V +10kV
Heater
Cathode
Focus electrodes
Correction
electrodes, ASTIG
etc.
X and Y deflection plates
PDA
connector
Phosphor coated screen
Figure 2.4a. Diagram of a typical Cathode-ray tube (CRT) construction.
A traditional analogue oscilloscope / analogue ECG machine draws its trace with a spot of light (produced by
a deflectable beam of electrons) moving across the screen of its CRT (see Figure 2.4b). Basically an
oscilloscope / ECG consists of the CRT, a ‘time base’ circuit to move the spot steadily from left to right
across the screen at the appropriate time and speed, and some means (usually a ‘Y’ deflection amplifier) of
enabling the signal to deflect the spot in the vertical or Y direction.