HP 8647A Operation And Service Manual page 113

The post regulating circuitry contains regulators for
+
12V, -12V and
+ 5
V
(shown as +5V(F1)). There is additional circuitry to derive a
filtered
+
5
V
from the power supply
+
5 V for the digital circuitry.
The
+
12 and + 5 V regulators are driven by the
+
15
V
supply from
the A2 assembly. The -12
V
regulator is driven by the -15
V
supply
from the A2 assembly. There are indication LEDs on the motherboard
for the five power supplies
that
are
lit
when the power supplies are
on.
The diagnostic latches latch signals from around the instrument that
are read by the controller during power-up.
A4 Reference The reference assembly accepts either an external 10 MHz reference
signal to lock the internal 10 MHz TCXO (temperature-compensated
crystal oscillator) or uses an optional high stability 10 MHz OCXO
(oven-controlled crystal oscillator). The reference assembly outputs
two 200 kHz signals, a 1 GHz signal, and a 10 MHz signal which is
routed to the rear panel.
One of the two 200 kHz signals
is
routed to the A5 synthesizer and
the other to the A3 modulation section. The 1 GHz signal is routed to
the A6 output assembly.
The 10 MHz REF OUTPUT rear-panel signal is a buffered output from
the 10 MHz TCXO or OCXO.
The 200 kHz signals are derived by dividing the 10 MHz signal by 50.
The 1 GHz signal is derived from a 1 GHZ VCO that is phase-locked to
the 10 MHz signal.
The reference assembly contains a calibration ROM that contains
factory-generated calibration data that is specific to the assembly.
A5 Sig Gen Synth
The synthesizer assembly uses a 200 kHz reference signal from the A4
reference assembly and generates a 500 to 1000 MHz signal using a
divide-by-n phase-locked loop VCO. Frequency and phase modulation
are also done in the synthesizer assembly. The frequency is modulated
both inside and outside of the loop bandwidth. F M outside
of
the
loop bandwidth is summed with the integrator error voltage and
applied directly to the VCO. FM within the loop bandwidth and phase
modulation signals are applied to a phase modulator along with the
signal from the divide-by-n circuitry and then applied to the phase
detector.
The synthesizer assembly contains a calibration ROM that contains
factory-generated calibration data that is specific to the assembly.
A6 Output The output assembly takes the 500 to 1000 MHz signal from the A5
assembly and the 1
GHz LO signal from the A4 assembly to generate
the output frequency range of 0.25 to 1000 MHz in three bands. The
output assembly also handles the filtering, AM, and amplitude leveling
functions.
The three frequency bands range from 0.25 to 249 MHz, 249 to 501
MHz, and 501 to 1000 MHz. The 0.25 to 250 MHz band is heterodyned
from the 1 GHz LO signal and the 500 to 1000 MHz main band signal.
5a.4
Theory of Operation