Section 4: Multi-frequency capacitance-voltage unit Model 4200A-SCS Parameter Analyzer Reference Manual4-18 4200A-901-01 Rev. C / February 2017ABB unbalance errorsThe 4210-CVU uses the autobalancing bridge (ABB) technique to achieve accurate impedancemeasurements. The ABB creates a virtual ground at the DUT to minimize measurement error. EveryCVU measurement is made with ABB active. The ABB always attempts to lock the low side of theDUT to virtual ground.If the ABB fails to lock, the measurement is made, but may be out of specification. If this occurs, thereturned 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 Irange setting• Too much parasitic load on the low side of the DUTYou can use Confidence Check (on page 4-19) to help troubleshoot ABB errors.CVU Real-Time Measure ModeThe CVU Real-Time Measure Mode provides a direct real-time user interface to the CVU to help youset up and debug your system. For example, you can use it to confirm that contact has been madewith the pads on a wafer. The measurements are independent of the open and short confidencechecks.To make real-time measurements:1. In Clarius, select Tools. The Clarius Tools dialog box opens.Figure 96: Clarius Tools dialog box2. Select CVU Real-Time Measure Mode.
