Ammeter Section; Reference Current Source; I-V Converter Block Diagram - Agilent Technologies 4339B Service Manual

Ammeter Section

The ammeter section converts current owing into to corresponding digital data. The section
includes an I-V converter, reference current source, and the Analog-to-Digital Converter.
I-V Converter. Figure 4-5 shows the I-V converter block diagram.
Figure 4-5. I-V Converter Block Diagram
The I-V Converter is essentially an integrator composed of an operational ampli er and a
capacitor. When current Ix ows into the integrator, the current charges capacitor C. As a
Ix
result, the integrator outputs a negative going ramp of which slope is . The current Ix
C
1
v
can be obtained by , where 1t is a certain time interval, and 1v is the output voltage
C
1
t
drop for this interval. Capacitor C, which is called range capacitor, determines the applicable
measurement range in a practical integrator.
Reference Current Source. The Reference Current Source is an internal current reference,
which provides the I-V converter with some sets of pre-de ned dc currents. The source is used
for the power-on self test sequence and for the calibration function.
T roubleshooting 4-7