The Commando
Newbie level 5
- Joined
- Sep 30, 2011
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- Alexandria, Egypt
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Hi ,
I am designing an LC VCO ... So I need a varactor ... when I connect the varactors RIGHT, I mean the positive terminals to oscillating nets and the -ve terminal to ground, the oscillating frequency does not vary with varying control voltage ... So, I folded the varactors, it worked ! ... But with -ve Kvco , increasing control voltage leads to decrease in frequency ...... When I fold the varactor and plot C-V curves, the curve has positive slope !!! capacitances is increasing with voltage .... when -using same circuit(s)- putting the varactor non-folded, it gives normal C-V curves with negative slope ...... I plotted C-V curves using sp analysis AND using ac analysis (measuring current) , and both give same results ...... sorry for long post, but I tried to be clear enough ....... Any explanation ??
I am designing an LC VCO ... So I need a varactor ... when I connect the varactors RIGHT, I mean the positive terminals to oscillating nets and the -ve terminal to ground, the oscillating frequency does not vary with varying control voltage ... So, I folded the varactors, it worked ! ... But with -ve Kvco , increasing control voltage leads to decrease in frequency ...... When I fold the varactor and plot C-V curves, the curve has positive slope !!! capacitances is increasing with voltage .... when -using same circuit(s)- putting the varactor non-folded, it gives normal C-V curves with negative slope ...... I plotted C-V curves using sp analysis AND using ac analysis (measuring current) , and both give same results ...... sorry for long post, but I tried to be clear enough ....... Any explanation ??