HP 70427A User Manual page 498

Overview
Looking at the Block
Diagram and
Schematics
YIG-Tuned-Filter (YTF) and GaAs FET Amplifier Driver Assembly
YIG-Tuned-Filter (YTF) and GaAs FET
Amplifier Driver Assembly
The YTF and GaAs FET amplifier driver assembly is common to all
modules in the HP 7042x family. This assembly provides the bias necessary
to operate one 2.4 GHz to 26.5 GHz YTF, one three-stage 2.4 GHz to 26.5
GHz GaAs FET pre-amplifier microcircuit, and one three-stage 2.4 GHz to
26.5 GHz GaAs FET power amplifier microcircuit.
The YTF assembly uses a 6-bit parallel data bus to transfer data into the four
12-bit Digital-to-Analog converters (DAC). The DACs control YTF main
tuning, YTF fine tuning, output amplifier level, and the auxiliary
TUNE-SPAN output.
Digital Control
The digital interface into the YIG/GaAs amplifier driver assembly is a
high-speed parallel interface to accommodate the large amount of data
necessary to set frequency and amplitude. It consists of a 6-bit parallel data
bus, a 3-bit address bus (which is used to select where data is to be
transferred) and an enable transfer line.
The data transfer occurs in several steps. First, the 6-bit data word is stored
in one of three 6-bit data latches. Data latch 0 and data latch 1 are used to
reconstruct the 12-bit parallel word required for the 12-bit DACs. Finally,
the reconstructed 12-bit word is transferred into the 12-bit DACs. Data latch
7 stores the 4-bit diagnostic multiplexer control, the amplitude mode control,
and the noise filter enable control.
Data is stored in each latch by placing the data on the data bus, addressing
the latch in which the data is to be stored, and enabling the transfer. The data
is then transferred into the desired 12-Bit DAC once both halves of the 12-bit
word are present in Latch 0 and Latch 1. The data is transferred by
addressing the desired DAC, and then enabling the transfer.
YTF and GaAs Amplifier Power-On Control
The address bus also enables the +10.00 volt reference after the DACs have
been initialized at module turn-on to prevent possible main frame current
overload shutdown. The four DACs contain random data at module
power-up. This data often sets all four DACs to the maximum output setting.
This combined with the capacitor inrush current in the module's power
supply allows the module to exceed its maximum current consumption limits
for an MMS {4}over{8}-module. If two HP 7042x modules are in the same
HP 70001 Main Frame, and both exceed the maximum current consumption
HP 70427A/HP 70428A User's Guide 13-63
Block Diagram