henry98
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Sheldon, I have also met the same problem. When you added the two differential preamplifiers between the VCO and the divider, these two differential preamplifiers may not be switched fully by the VCO output voltage. Especially f or the first one. For example if the VCO output voltage is between 1.8 to 2.5v; We can use the first Pre_amplifer to increase the output swing, if amplifying 2 times, then we can got the output swing: (2.5-1.8)*2=1.4v. But this first stage pre_amplifier maybe not fully swithched by the VCO output voltage(1.8 to 2.5v), so after first amplified, the votage maybe in the range 0.9 to 2.3v. And it can't reached to vdd=2.5v. That means the first pre_amplifier can't be fully switched by the VCO output swing. IF such things happened, Could these pre_amplifiers still be thought as work very well?
Thanks
Henry
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