Tektronix FG 5010 User Manual

Theory of
Operation
- FG 5010
13B
>>
FM / VCF
INPUT
F
4-8
Ø LOCK
FREQ CONTROL
VOLTAGE
+ 10.00V
REF
FO
*
U1731A
+1
U1731B
U1821C
FM
DATA
U1731C
U1821B
LOOP
CAL
U1821A
FREQ DACS
DATA
DAC
REF
AMP
12
BIT
Frequency
Reference
Selector
The purpose of this circuit is to produce the frequency
control voltage that is applied to the symmetry DAC circuits ,
depicted on
Diagram
11. The
Frequency
Reference
Selector
consists of three analog transmission gates , U1821A , B ,
and C ; and two amplifiers , U1731B and U1831 . The latter is
a
summing
amplifier
that
combines
the
inputs of
U1821B
( which applies the ø LOCK Freq control voltage to the sum
ming
point ) ,
U1821A ( which
applies
the
VCF
control signal
to
the
summing point ) , or the
output of
the Frequency
DAC
circuit , which is discussed later .
The LOCK Freq control voltage is applied to the Loop 1
Board at
P1510 pin 13B , from
where it is
applied to
analog
transmission gate U1821B , pin 4. If the LOCK control line
from latch U1702 pin 12 is low , U1821B is enabled to pass
the error signal to U1831 , thus giving the phase - lock section
low
- pass filter
from the
Loop 2
circuits the
control of
the
loop operating frequency .
REF
Ø LOCK
VCF
U1721
U17310
8
BIT
REF
U1612
U1621
H.
N
Fig . 4-3 . Loop 1 Reference simplified diagram .
1024
FREQUENCY
REFERENCE
SELECTOR
+
A
+
w
·
|
·
N
U1831
:
2
FREQ
CONTROL
VOLTAGE
3467-10
The
FM / VCF
input is
applied
through P1560 to the
noninverting
input of
amplifier
U1731B ,
which
acts
as a buff
er
with a gain
of one .
Diodes
CR1741 and
CR1841 limit the
input
voltage
swing to no
more than
4.6 V and
+11.4 V.
From U1731B pin 14 , the signal is applied to U1821A and
U1821C . In the
first case , if the
VCF control
line is low
(
U1702
pin
11 ) ,
U1821A passes
the
signal from
U1731B
through
U1821C to be
summed with
the +10
V reference
from U1731A , and applied to the inverting input of the DAC
Reference
Amplifier
.
Amplifier U1831 is the summing amplifier for the Fre
quency Reference Selector . Input currents from U1821A ,
U1821B , and the
Frequency
DAC
section are fed
individual
ly or in combination to pin 2 , the summing point of U1831 .
The
amplifier is
clamped at
10 V output by
VR1722
. This
prevents
overdriving the
amplifier when large
signals are fed
to the
summing
point
.
:)
C
U
11
J
U
U
U

Tektronix FG 5010 Specifications

General

Brand	Tektronix
Model	FG 5010
Category	Portable Generator
Language	English