Conductive EMI test system, a decoupling network therefor

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT FIG.
1 is a side view of a decoupling network within a block diagram of a bench test setup 10 for analyzing EMI.
A test item or device under test (DUT) 12 is coupled to its DUT support 14 via a decoupling network 16.
The support 14 provides all the power and data signals necessary to operate the DUT.
Illustratively, the DUT 12 may be an engine control system that includes a microcomputer as a controller and the DUT support 14 may be a simulator that makes the engine control system function just as it would in a vehicle providing, e.
g.
the necessary voltages and sensor inputs and output loads.
Coupled between the input l6L of decoupling network 16 and conventional measurement instrumentation 20, is a conventional high impedance probe 18 for coupling noise signals from the input side of the decoupling device to the instrumentation.
The instrumentation may be the type used to obtain time or frequency analysis data.
Decoupling network 16 presents a low passband to the signals from DUT support 14 necessary for DUT operation and essentially an open circuit impedance to signals from both the DUT and its support within a chosen frequency band.
Measurements of open circuit noise voltages from the DUT are desired.
When one is interested in open circuit voltage measurement, you load the DUT into the highest impedance one can reasonably obtain.
FIG.
2 is a block diagram illustratgive of test setup for evaluating worst-case noise potential of DUT 12, DUT 12, which receives support power from DUT support 14, includes a noise source with an unknown impedance.
High impedance decoupling network 16 impedance.
High impedance decoupling network 16 impels DUT 12 to emit worst-case noise voltage signals which measuring device 20 assesses.
To achieve this high impedance, a serially connected network of inductance resonators 16A through 16H of FIG.
1 has been developed which operate effectively over a broad band of frequencies shunted by a bank of parallel capacitors 16J which also operate over a broad band of frequencies