preference among nmos and pmos varctors in LC VCO

[venkateshjuturu]

hi everyone,
i have seen many LC Voltage Controlled Oscillators topologies where they used PMOS varactors as variable capacitors instead of NMOS
may i know why we cannot use NMOS varactors
thanks in advance

 

[erikl]

may i know why we cannot use NMOS varactors

Of course NMOS varactors can be used. NMOS accumulation varactors in n-well - due to their monotonic and less steep C-V characteristic - are more suitable for frequency tuning in phase-locked-loop applications, as the achievable lower modulation sensitivity makes VCOs less susceptible to noise, see e.g. para. 4.2.4 of this .

 

[venkateshjuturu]

Of course NMOS varactors can be used. NMOS accumulation varactors in n-well - due to their monotonic and less steep C-V characteristic - are more suitable for frequency tuning in phase-locked-loop applications, as the achievable lower modulation sensitivity makes VCOs less susceptible to noise, see e.g. para. 4.2.4 of this .

"thank you "