Function Selector
Function selection
is
achieved by S9 to
S11
switching
the selected waveform
onto
the (mixsig) line. Note
that S10 isolates both the
input
and
output
of
the
diode gate when the squarewave is deselected.
Output Amplifier
The input stage
is
formed
by
two
symmetrical
differ
-
ential amplifiers TR12
to
TR15. TR16
to
TR19 are
current mirrors
with
a current gain
of
approximately 3
determined
by
the emitter resistors. D18 and D19 bias
the class B output stage TR20 and TR21. Short circuit
protection is provided
by
R75 and R78.
The
voltage
gain
of
the amplifier
is
given
by
1 + (R79/R72) = 22.3.
VR18
is
used to
trim
out
any residual offset voltage.
VR
19
is the
front
panel
d.c.
offset control.
Attenuators
R80
to
R87
form
the
50Q
attenuator.
R88
to
R94
forni
the 600Q attenuator. The attenuators are controlled
by a three
way
interlocking switchbank S12
to
S14
giving attenuation factors
of
OdB,
- 20dB and
-40d8
.
CALIBRATION PROCEDURE
Refer
to
the component layouts on pages
10
and
13
to
locate the test points and variable resistors.
Before proceeding
to
calibrate
the
function generator
set the following controls
as
shown below.
Frequency Range
Function
Attenuator
DC offset
Amplitude
1.
Power
Supply
lkHz
Triangle
0dB
Centre
off
position
Centre
a)
Check Voltage
at
TP7
is
+ 15v ± 0.3v
b) Check Voltage
at
TP8
is
-15v
± 0.45v
2.
IC1, 2,
3,
4 DC
Offset
a)
Set VR4 fully anti-clockwise.
b) Measure the voltage
at
TP5
w.r.t
0V, adjust
VR1
to give reading
of
- 10.00mV ± 0.04mV.
c) Measure the voltage
at
TP6
w.r.t
Ov,
adjust VR3
to
give reading
of
+ 10.00mV ± 0.10mV.
d) Measure the voltage
at
TP4 w.
r.t
oV, adjust VR5
to
give a reading
of
- 10.00mV ± 0.10mV.
e)
Measure the voltage
at
TP2
w.r.t
TP7, adjust VR7
to
give a reading
of
- 33.33mV ± 0.17mV.
f)
Measure the voltage
at
TP3
w.r
.t TP8, adjust VR8
to give a reading
of
+ 33.33mV ± 0.17mV.
g) Re-check the voltage
at
TP5 and repeat the above
if it
has changed.
h) Set
VR1
to 2.0.
3.
Triangle Buffer
DC
Offset
a)
Turn
off
the power
to
the
unit,
and using a
short
length
of
wire short the junction
of
D2 and
D4
to
the ground plane.
b)
Connect a voltmeter between TP9 and ground
and turn the power back on.
c)
Adjust VR9 for a reading
of
0.0mv ± 0.5mv.
d) Turn
off
the power
to
the
unit
and disconnect the
short circuit.
e)
. Turn on the power to the unit.
4.
Triangle Amplitude
a)
Connect
an
oscilloscope and a voltmeter
to
TP9.
b)
Set
the Amplitude control
to
minimum.
c) Adjust
VR
10
and VR
11
until the triangle wave
is
1.0Vp-p and the
d.c.
offset
is<
1.0mV.
5.
Output Amplifier
DC
Offset
a)
Monitor
the 50!2
output
with a voltmeter.
b) Set the Amplitude control
to
its mid position and
adjust VR18
for<
10.0mv.
c) Rotate the Amplitude control from minimum
to
maximum and check
that
the de offset does
not
exceed ± 50mV.
6.
Frequency Calibration
a)
Select the 10kHz frequency range.
b) Connect a frequency counter
to
the
TTL
output.
c)
Set the frequency control
to
0.2 and adjust VR4
for a reading
of
2.0kHz ± 0.8kHz.
5
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