HP 8340A Service Manual page 281

voltage change of each summing amplifier ramp is added together,
the total will equal 10 volts,
during one sweep.
sweep Width DAC
The Sweep Width DAC performs two functions.
its input by a factor of 1,
harmonic is being swept.
give the appropriate sweep width.
determined jointly by the sweep Width DAC and the sweep Width
Range Attenuator
(Block N) selects the correct decade range,
DAC then interpolates within that selected range.
Width DAC attenuation factors are multiplied together by the
instrument processor,
input of the sweep Width DAC.
CR5 protects Ull,
+5 volt supply comes up before the +15 volt supply.
CR5 in the event that the +15 volt supply is shorted to ground.
CR6 protects the output of Ull by keeping it from going much
below ground.
To check out this DAC,
band sweep to stop the sweep with Marker Ramp at +10 volts.
voltage at TP2
also be at +10 volts.
directly and the output voltage at TP8
DAC Block M) observed.
volts out, and an input of 4096 should give +10 volts out.
sweep Width Range Attenuator
R58, R59, R61,
voltage at each node is a factor of 10 smaller than the voltage
at the node above it.
that the impedance at each node is low and approximately equal.
This was necessary in order to reduce the susceptibility to
radiated noise.
appropriate node.
VSWP line.
In instrument sweeps of greater than 5 GHz,
necessary in this block.
the output of Ul6 is fed to the buffer.
Only one of the FET switches in this block should be on at any
given time. VSWP is fed back to U36 in Sweep Width Range Switch
Driver (Block
8-368
Model 8340A - Service
M
2,
Secondly,
(Block N) The sweep Width Range Attenuator
•
and the result is applied to the digital
which is a CMOS device,
C39 is a compensation capacitor.
use the "SHIFT,
(RST RMP in summing Amplifier,
Now the sweep Width DAC can be programmed
A digital input of zero should give zero
and R62 form a decade voltage divider stack.
This particular arrangement was used so
Q8, QlO, or Ql 2 is turned on to select· the
Ul 7 is a unity gain buffer which drives the
To acc.omplish this,
F) and becomes the supply voltage for the range
Scans by HB9HCA and HB9FSX
regardless of the number of ramps
First,
3 or 4 depending upon which
it attenuates its input to
The actual sweep width is
and the Sweep Width
in the event that the
XTAL" function in a single
( 20-30 SWP in Sweep Width
N
a gain of six is
Q7 is turned on and
it attenuates
The two sweep
CR7 protects
The
Block L) should
The