#### scooby-doo

##### Newbie level 1

Hey all,

I want do design a current starved inverter based vco.

to achieve a linear voltage-to-frequency transfer characteristic i built already a linear voltage to current converter which supplies the input current for the vco.

this current is mirrored by simple current mirrors into the vco.

i designed the pmos transisotrs to be 10/1 and the nmos transisors to be 5/1.

(1 is the shortest lenght in process)

this allows me equal delays for rising and falling edges and an equal current in the sourcing/sinking device during transition.

as far as i know the frequency is determinded by fosc=I/(N*C*Vswing)

where I= current through inverter

N=number of stages

C=parasitic capacitance of inverter

Vsing=Voltage swing of inverter.

therefor I assumed a linear relation between my input current and the oscillation frequency.

but if I look at my transfercaracteristic I see a perfect quadratic behaviour between current and frequency. it´s looking close to linear but there is still a visible arc within my transfer characteristic.

does anyone know where that could come from and what i could do to make in more linear?

I want do design a current starved inverter based vco.

to achieve a linear voltage-to-frequency transfer characteristic i built already a linear voltage to current converter which supplies the input current for the vco.

this current is mirrored by simple current mirrors into the vco.

i designed the pmos transisotrs to be 10/1 and the nmos transisors to be 5/1.

(1 is the shortest lenght in process)

this allows me equal delays for rising and falling edges and an equal current in the sourcing/sinking device during transition.

as far as i know the frequency is determinded by fosc=I/(N*C*Vswing)

where I= current through inverter

N=number of stages

C=parasitic capacitance of inverter

Vsing=Voltage swing of inverter.

therefor I assumed a linear relation between my input current and the oscillation frequency.

but if I look at my transfercaracteristic I see a perfect quadratic behaviour between current and frequency. it´s looking close to linear but there is still a visible arc within my transfer characteristic.

does anyone know where that could come from and what i could do to make in more linear?

Last edited: