Elenco 100kHz Function Generator - Manual (Page 3)

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INTRODUCTION
Your FG-500 Function Generator contains a complete function generator capable
of producing sine, square and triangle wave forms. The frequency of this generator
can be continuously varied from 1Hz to 1MHz in 6 steps. A fine frequency control
makes selection of any frequency in between easy. The amplitude of the sine and
triangle waveforms are adjustable from 0 to 3Vpp. This complete function generator
system is suitable for experimentation and applications by the student. The entire
function generator is comprised of a single XR-2206 monolithic IC and a limited
number of passive circuit components. The unit is powered with a 9V battery.
THEORY OF OPERATION
The heart of the FG-500 Function Generator is the XR-2206 monolithic
function generator integrated circuit. The XR-2206 is comprised of four main
functional blocks as shown in the functional block diagram (Figure 1). They
are:
• A Voltage Controlled Oscillator (VCO)
• An Analog Multiplier and Sine-shaper
• Unity Gain Buffer Amplifier
• A set of current switches
The VCO actually produces an output
frequency proportional to an input
current, which is produced by a resistor
from the timing terminals to ground. The
current switches route one of the
currents to the VCO to produce an
output frequency. Which timing pin
current is used, is controlled by the FSK
input (pin 9). In the FG-500, the FSK
input is left open, thus only the resistor
on pin 7 is used. The frequency is
determined by this formula:
f
o
= 1/RC Hz
where f
o
is the frequency in Hertz
R is the resistance at pin 7 in Ohms
C is the capacitance across pin 5 and 6 in Farads
Note that frequency is inversely proportional to the value of RC. That is,
the higher the value of RC, the smaller the frequency.
The resistance between pins 13 and 14 determine the shape of the output
wave on pin 2. No resistor produces a triangle wave. A 200
Ω resistor
produces a sine wave.
FUNCTIONAL BLOCK DIAGRAM
1
2
3
4
5
6
7
8
14
Figure 1
Current
Switches
VCO
Multiplier
and
Sine
Shaper
+1
AM Input
Sine/Saw
Output
Mult. Out
V+
Timing
Capacitor
Timing
Resistor
Symmetry
Adjust
Waveform
Adjust
Ground
Sync
Output
Bypass
FKS
Input
15
16
13
12
11
10
9