Purpose: To describe a calibration technique for the purpose of calibrating for path loss from a WF to the fixture top. At low frequencies the path loss through a cable from a WF may be low. Insertion of pads or switches can add significant path loss and need to be accounted for.
Example: Using an oscilloscope to perform a low freq (100KHz - 1.8MHz) scalar calibration on WF2.
- First the WF2 cable is detached from any circuitry inside the fixture and adapted to an external oscilloscope. The oscilloscope is set to measure into a 50 ohm impedance since this is the environment in which the WF will be fed during the application.
- During the first portion of test the oscilloscope Vpp output is prompted from the user. It is then converted to rms voltage ( /2.828) and then to power. It is then loaded into the local variable "WF2 Cal Standard". This measurement establishes the response of WF2 prior to the fixture circuitry. It is thus called "WF2 Cal Standard" in the Array LV (figures 1, 2, and3).
Figure 1 Global Defaults
Figure 2 Measure Standard Vin WF2 Setion Defaults
Figure 3 Measure Standard Vin WF2 Test Panel
- Next the WF2 cable is reattached to the fixture circuitry. The oscilloscope is then attached to the top side fixture port related to the WF2 resource. In this example it is DutRF8.
- The same frequncies and amplitude used in the first portion of the test are then repeated and again the output of the oscilloscope is prompted from the user. The results are converted to power and loaded into the local variable "WF2 Cal" (figure 4).
Figure 4 Measure Loss Vin WF2 Test Panel
Figure 5 Calc Difference
- The difference between "WF2 Cal Standard" and WF2 Cal is calculated and converted into log format (figure 5). The difference is then placed into the final fixture cal factor named PathWF2DutRF8WF2" (figure 6).
Figure 6 Calc Final