Fluke 5520A - Encoder Assembly (A2); Synthesized Impedance Assembly (A5)

5520A
Service Manual
2-4
2-2. Encoder Assembly (A2)
The Encoder assembly (A2) has its own microprocessor and is in communication with
the Main CPU (A9) on the Rear Panel through a serial link. Memory for the Encoder
assembly is contained in EPROM. The Encoder assembly handles the interface to the
Keyboard assembly (A1).
2-3. Synthesized Impedance Assembly (A5)
The Synthesized Impedance assembly (A5) generates variable resistance and capacitance
outputs. It uses discrete resistors and capacitors as references, with an amplifier in series.
Figure 2-2 is a block diagram of the synthesized resistance function. Figure 2-3 is a block
diagram of the synthesized capacitance function.
For resistance synthesis, there is a two-wire compensation circuit, an input amplifier, two
DACs (coarse and fine) with offset adjust, and an output LO buffer.
For capacitance synthesis, there is a two-wire compensation circuit, selectable references,
an input amplifier, two DACs (coarse and fine), and an output LO buffer.
+
_
DAC
NORMAL HI
R
x
=
R
ref
RCOM
NORMAL LO
yg117f.eps
Figure 2-2. Synthesized Resistance Function