4: Multi-frequency capacitance-voltage unit Model 4200A-SCS Parameter Analyzer
4-18 4200A-901-01 Rev. C / February 2017
ABB unbalance errors
The 4210-CVU uses the autobalancing bridge (ABB) technique to achieve accurate impedance
measurements. The ABB creates a virtual ground at the DUT to minimize measurement error. Every
CVU measurement is made with ABB active. The ABB always attempts to lock the low side of the
DUT to virtual ground.
If the ABB fails to lock, the measurement is made, but may be out of specification. If this occurs, the
returned data is flagged and shown in yellow on a blue background on the Analyze sheet.
Most common reasons that the ABB fails to lock are:
• The cable lengths on the CVU terminals are not the same
• HPOT or LPOT terminals were disconnected
• Excessive noise on the LPOT terminal
• High frequency sources
• Physical cable lengths do not match the cable length set in Clarius
• Improperly torqued SMA cables
• Sub-optimal I
range
setting
• Too much parasitic load on the low side of the DUT
You can use Confidence Check (on page 4-19
) to help troubleshoot ABB errors.
CVU Real-Time Measure Mode
The CVU Real-Time Measure Mode provides a direct real-time user interface to the CVU to help you
set up and debug your system. For example, you can use it to confirm that contact has been made
with the pads on a wafer. The measurements are independent of the open and short confidence
checks.
To make real-time measurements:
1. In Clarius, select Tools. The Clarius Tools dialog box opens.
Figure 96: Clarius Tools dialog box
2. Select CVU Real-Time Measure Mode.
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