HP 3312A Service Manual

Model 3312A
Section IV
SECTION IV
THEORY OF OPERATION
41. INTRODUCTION.
4-2. This section contains a complete theory of operation
for the Model 3312A Function Generator. The theory is
divided into two levels:
1. Basic Block Diagram Description
2. Functional Block Diagram Description
Detailed circuit descriptions are given for unique complex
circuits. These descriptions may be helpful when trouble-
shooting the instrument.
43. DESCRIPTION.
4-4. The 3312A combines two separate, independent func-
tion generators referred to as the main generator and the
modulation generator. The main generator output can be
controlled by the modulation generator. The major features
of the 3312A are the 0.1 Hz to 13 MHz frequency range of
the main generator and the AM, FM, sweep and tone burst
capabilities of the modulation generator. A basic block
diagram of the 3312A is shown in Figure 4-1,
4-5, BASIC BLOCK DIAGRAM DESCRIPTION.
4-6.
The
main.
generator
of
the
3312A
uses
a
voltage
to
frequency
conversion
technique.
A
triangle
waveform
is
generated
by
charging
and
discharging
a
capacitor
from
a
constant
current
source.
The
time
required
to
charge
and
discharge
the
capacitor
determines
the
period
of
one
cycle
and,
therefore,
the
frequency.
VOLTAGE
_ [COMPARATOR
ji
= i
TUNING |, | TRIANGLE (^V
AMPLIFIER GENERATOR
BURST CONTROL
CONTROL
FM AND SWEEP CONTROL GENERATOR
3312 A B 3954
| SINE av
SHAPER
a MODULA ON OE ele ecaaadaniliad
4-7.
The
triangle
waveform
from
the
Triangle
Generator
is
applied
to
the
Voltage
Comparator
which
acts
as
an
amplitude
limiter.
As
the
triangle
waveform
alternately
crosses:
the
upper
and
lower
switching
levels
of
the
limiter
input,
a
square
wave
is
generated
at
the
output
of
the
Voltage
Comparator,
This
square
wave
is
fed
back
to
the
Triangle
Generator
where
it
controls
the
charge/discharge
cycle
of
the
triangle
output.
4-8. To obtain a sine wave, the triangle wave is shaped by a
diode network in the Sine Shaper. The diode network
serves as a non-linear load which varies the attenuation of
the input triangle according to its level.
4.9. The modulation generator can amplitude modulate,
frequency modulate, sweep, or initiate a burst from, the
main generator output. Sweep and frequency modulation
modes control the voltage output of the tuning amplifier
which determines the frequency. In amplitude modulation,
the main signal is routed through a balanced modulator
where it is mixed with the modulating signal. The percent
of modulation is controlled by the level of the modulating
signal.
4-10. The tone burst is accomplished by gating the main
generator output on and off. Multiple or single cycle
operation is determined by the duration of the low state of
the Burst Control.
4-11. The output amplifier has separate parallel paths for
the high and low frequencies. This gives it wide bandwidth
and a high slew rate to maintain good square and triangle
wave shape without compromising de stability and low
offset. An integrated-circuit operational amplifier is used
Bickel AS ahhh, A
OC OFFSET
i
OUTPUT
A
P
pat-
AMPLIFIER
ATTENUATOR
g
[10
|:
100
H:
1000
|
AMPLITUDE
MODULATOR
Figure 4-1. Basic Block Diagram.
4-]

HP 3312A Specifications

General

Brand	HP
Model	3312A
Category	Inverter
Language	English