15
Differential and Pseudo-Differential Input Configuration
The PCIe-69529 provides both differential and psuedo-differential input configurations,
with differential input mode providing voltage to the anode and cathode inputs of the
SMB connector according to signal voltage difference there between. If the signal source is
ground-referenced, differential input mode can be used for common-mode noise rejection.
If the signal source is a floating signal, pseudo-differential input mode can provide a
reference ground connected to the cathode input of the SMB through a 50 Ω resistor,
preventing the floating source from drifting over the input common-mode range.
Recommended configurations for the signal sources are as follows.
Signal Source Type
Card Configuration
Floating
Pseudo Differential
Ground-Reference
Differential
AC and DC Input Coupling
AC and DC coupling are available. With DC coupling, DC offset present in the input signal
is passed to ADC, and is indicated if the signal source has a small level of offset voltage or
if DC content of the signal is important. In AC coupling, the DC offset present in the input
signal is erased, and is indicated if the DC content of the input signals is to be rejected. AC
coupling enables a high pass R-C filter through the input signal path. The corner frequency
(-3dB) is about 0.5Hz.
Input for IEPE
For applications that require sensors such as accelerometers or microphones, the PCIe-
69529 provides an excitation current source. The common excitation current is usually
about 4mA for these IEPE sensors. A DC voltage offset is generated due to the excitation
current and sensor impedance. When IEPE current sources are enabled, the PCIe-69529
automatically sets input configuration to AC coupling.
3�2�2 Input Range and Data Format
When using an A/D converter, properties of the signal to be measured should be considered
prior to selecting channel and signal connection to the module. A/D acquisition is initiated
by a trigger source, which must be predetermined. Data acquisition commences once
the trigger condition is established. Following completion of A/D conversion, A/D data is
buffered in a Data FIFO, and can then be transferred to PC memory for further processing.
Transfer characteristics of the two input ranges of the PCIe-69529 are as follows. Data
format of the PCIe-69529 is 2’s complement.
Description
Full-scale range
Least significant
bit
FSR-1LSB
-FSR
Bipolar Analog
Input
±10 V
1.19 μV
9.99999881 V
-10 V
±1V
0.119 μV
0.999999881V -1 V
Digital Code
N/A
N/A
7FFFFF
800000
Table 3-1: Input Range and Data Format
