If Amplifier; Linear Amplifier - HP 3580A Operating And Service Manual

Model 3580A
GAIN CONTROL
~IHz
GAIN
ADJ
RI
~3Hz
GAIN
ADJ
R2
~
IOHz
GAIN
TPI
ADJ
IOOkHz
R3
INPUT ~
30Hz
FROM
GAIN
IF
ADJ
FILTER
R4
~IOOHz
GAIN
ADJ
CR2
R5
CR3
RIG
300Hz IOOHz 30Hz IOHz
35SOA - B- 3549
BANDWIDTH LINES
Figure 4-4.
4-51. IF Amplifier.
The IF Amplifier section (Figure 4-4)
consists of a Gain Control circuit and an LCR-tuned IF
Amplifier.
4-52. Gain Control Circuit. The gain of the IF Amplifier is
determined by the input resistance provided by the Gain
Control circuit and by the impedance of the parallel LCR
network in the feedback loop. The Gain Control circuit has
six
resistive input branches. The input branches are individ-
ually switched into the circuit by transistor and diode
switches controlled by lines from the BANDWIDTH switch.
With the exception of the 300 Hz branch, each section of
the Gain Control circuit contains a variable resistor. This
provides a separate gain adjustment for each BANDWIDTH
setting. The separate gain adjustments compensate for gain
variations that occur in the Input Mixer and IF Filter.
INPUT
Section IV
IF
,.GAIN
ADJ
:fB
i
I I
TP2
I
R47 I
C9 I
I
IOOkHz
IF OUT
TO
LINEAR
AND LOG
AMPS
3Hz I Hz
IF Amplifier.
4-53. IF Amplifier. The IF Amplifier is a 3-stage amplifier
circuit which is tuned to 100 kHz by the parallel resonant
tank circuit in the feedback loop. The 3 dB bandwidth of
the amplifier is approximately 1.2 kHz. The IF Amplifier
has a low-impedance complementary-symmetry output
stage which drives the following log and linear amplifier
stages. The full-scale signal level at the output (TP2) of the
IF Amplifier is approximately 2.8 V rms on all six
BANDWIDTH settings.
4-54. Linear Amplifier.
The Linear Amplifier (Figure 4-5)
consists of an Input Attenuator, an Input Amplifier, an
Output Attenuator and an Output Amplifier. The Input
Attenuator is controlled by the front panel AMPLITUDE
REF LEVEL switch and provides either - 40 dB or 0 dB of
AMPLITUDE INPUT
REF LEVEL SENSITIVITY
y
0
I
I
I I
I
I
F
ATTENUATOR=\
r---------------1--------7
I
I
I
I
I
IOOkHz
I NPUT---110-----1
FROM
IF AMP
3580A-B-3550
OdB
I I
I
I
I
~
I
I
'n-----1
-40dB TO-IOdB
OUTPUT
ATTENUATOR
LINEAR MODE SELECT
Figure 4·5. Linear Amplifier.
4-5