Overall Block Diagram; Analog Section - Agilent Technologies 4349B Service Manual

Overall Block Diagram

Figure 4-2 shows the overall block diagram of the 4349B.
The 4349B has four channel inputs, or two channel inputs for Option 001. Each I-V converter,
which is directly connected to an input connector, converts the current to a voltage ramp
of which slope is proportional to the input current. A demultiplexer selects the channel to
be measured and passes the voltage ramp to the analog-to-digital converter (ADC). The CPU
calculates the current from the voltage ramp slope, then calculates the DUT resistance by
dividing the measurement voltage by the current.
The measurement voltage is data which must be input from the keyboard or by
Note
GPIB commands. The 4349B itself has neither voltage output capability nor
voltage measurement capability.

Analog Section

Figure 4-3 shows the Analog Section block diagram.
An external dc voltage source applies measurement voltage to the DUT with the I-V Converter
connected in series. The DUT is connected to the 4349B measurement channels by a triaxial
cable which is a three layered coaxial cable. This triaxial cable prevents noise and improves
the contact check function accuracy. The current ows into the I-V Converter via the contact
check transformer. As discussed in \I-V Converter", the I-V Converter converts current owing
into to voltage ramp. The attenuator and normalization ampli er enhances the number of
measurement ranges and of measurement speed selections using fewer range capacitors. The
demultiplexer selects the measurement channel by selecting one of four (or two for Option 001)
I-V converter output voltage ramps. The voltage ramp slope, which is proportional to the I-V
Converter input current, is determined by di erence between two voltage measurement results
in a certain time interval.
4-4 T roubleshooting
Figure 4-2. 4349B Overall Block Diagram