Crystal Instruments Spider - Page 70

Spider DSA User’s Manual
70
Cal Circuit
Analog Input
Charge Circuit
TEDS
Detection
IEPE Power
ADC
DSP
Amplifier
With GAIN 1
AC HP Filter
or
DC
Single-
End or
Diff.
ADC
Amplifier
With GAIN 2
Figure 21:Typical Input Block Diagram (Spider-80x and Spider-81)
Figure 22: Single-Ended vs. Differential input
There are six modes in which the inputs can operate for the Spider-80X and the
Spider-81 series. The Spider-20 only has DC-single end, AC-single end, and IEPE
modes.
DC-Differential
In DC-Differential mode, neither of the input connections is referenced to the
local ground. The input is taken as the potential difference between the two input
terminals, and any potential in common with both terminals is canceled out. The
Common Mode Voltage (CMV) will be rejected as long as the overall input voltage
level does not saturate the input gain stage. Beware that very high CMV will cause
Vcc
Input
Terminals
+
-
Vin
Input Amp
Single-Ended
Vcc
Input
Terminals
+
-
Vin
Differential
Input Amp