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VCO and buffer waveform problem

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happsky

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This a single end waveform of a cross-couple VCO,the larger one is from vco ,and the other is the buffer output,the buffer is a common source amplifer with a differential inductor at the top.

why the buffer output waveform is so strange, and will it degrade PN of vco?

thank you very much!
 

Source/emitter/cathode followers all suffer from th same effect:- on positive going signals the device "switches on" and its output impedance is ~ i/gm || Rs/Re/Rk. On negative going signals, the device will try to switch off due to stray capacity holding the source positive while the gate goes negative, hence the output impedance will be Rs/re/Rk. This would account for the assymetry of the wave form. Exactly what is happening around the zero volts is another matter. Is your Vdd clean?
Frank
 

Yes,it clean ,it a ideal VDC
chuckey said:
Source/emitter/cathode followers all suffer from th same effect:- on positive going signals the device "switches on" and its output impedance is ~ i/gm || Rs/Re/Rk. On negative going signals, the device will try to switch off due to stray capacity holding the source positive while the gate goes negative, hence the output impedance will be Rs/re/Rk. This would account for the assymetry of the wave form. Exactly what is happening around the zero volts is another matter. Is your Vdd clean?
Frank
Click to expand...
 

use the Pseudodifferential amplifer as buffer out, or use the cap:ac couple to a INVERT shorted by one resistor about kOM
 

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