Calibrator
Theory of Operation
19
Current PCA (A7)
The Current PCA outputs six current ranges (330 μA, 3.3 mA, 33 mA, 330 mA,
3 A, and 20 A) and three voltage ranges (330 mV, 3.3 V, and 5 V) to the AUX
outputs. The 20 A outputs are sourced through the 20 A AUX binding posts.
The Current PCA connects to the DDS PCA (A6). The Filter PCA (A12) supplies
the high current power supplies.
The Current PCA (A7) has these functional blocks:
• Transconductance amplifier.
• Precision current shunts and amplifier. (These are the elements that set
accuracy.)
• AUX voltage function.
Power for the Current PCA is provided by the Filter PCA (A12).
Figure 5 is a block diagram of the current function. Note that the DDS PCA works
together with the Current PCA to supply current outputs.
IDAC
ICOM
SCOM
DDS PCA (A6)
Current PCA (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
yg119f.eps
Figure 5. Current Function (AUX Out Ranges)
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