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the strange warning of IC-cap

Question asked by elone on Sep 3, 2007
Hi guys,
I met a problem when I use IC-Cap, together with NWA 8510C, HP4142 etc., to measure the DC parameters of a power amplifier. In my case, I assign the gate voltage(Vg) and drain voltage(Vd) as two inputs and the output is drain current(Id). As I start to measure the Id, the IC-Cap continues to report two warnings: 1.SMU1—other channel compliance error; 2.SMU1: oscillation or Pulse width too small.  The SMU1 refers to the Vg and its compliance is 20mA and SMU2 refers to Vd with 600mA as its compliance. In the process of measurement, oscillation occurred definitely. However, the maximum Id is no more than 400mA and measured Ig(the measured gate current from SMU1) is no more than 150uA, none of them are out of compliance range. Why IC-Cap reports the first warning?  Thanks in advance.

Here are my settings:
Input: Vg                    
Mode: V                              
+Node: G                              
-Node: Ground                    
Unit: SMU1                         
Compliance: 20m                    
Sweep type: LIN                    
Sweep order: 2                    
Start:-2                                
Stop: 0                              
Of points: 21                         
Step size: 100m                    

input: Vd 
Mode: V
+Node: D
-Node: Ground
Unit: SMU2
Compliance: 600m
Sweep type: LIN
Sweep order: 1
Start: 0
Stop: 6.0
Of points: 21
Step size: 300m  

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