5500A
Service Manual
2-6
The dual-channel DDS (Direct Digital Synthesizer) generates finely stepped digital
waveforms that take the form of sine, triangular, and other waveforms.
2-5. Current Assembly (A7)
The Current assembly outputs six current ranges (330 uA, 3.3 mA, 33 mA, 330 mA, 2.2
A, and 11 A) and two voltage ranges (330 mV and 3.3 V) to the AUX outputs. The
330 uA range is only available in ac. If a 5725A Amplifier is attached, 5500A current
can also be sourced through the 5725A binding posts.
The Current assembly works together with the DDS (A6) assembly. The Filter (A12)
assembly provides the high current power supplies.
The Current assembly (A7) contains the following blocks:
• A floating supply.
• Several stages of transconductance amplifier.
• Current-sensing shunts and shunt amplifier. (These are the accuracy-setting
elements.)
• AUX voltage function.
Operating power for the Current assembly is filtered by the Filter assembly (A12). Its
common is separated from SCOM by a shunt resistor.
Figure 2-4 is a block diagram of the current function. Note that the DDS assembly works
together with the Current assembly to generate current outputs.
IDAC
ICOM
SCOM
DDS Assembly (A6)
Current Assembly (A7)
AC
Converter
IDAC Error
Amp
DDS
Ch 1
Current
Amp
Shunt
Amp
Shunt
AUX HI
AUX LO
ac
dc
dc
Ref
ac
SCOM
SCOM
±
SCOM
om006f.eps
Figure 2-4. Current Function
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