Oscillator design (Bandgap Current)

[analog_design255]

I want to build a relaxation oscillator like the schematic but I should have to use a bandgap reference voltage to create a stable current for the charge and discharge of the capacitor.
I want to use a Schmitt trigger and a feedback path which consists of two inverters. What does it mean with VCCS (Voltage controlled current source?). Are these two inverter the place where I can put the current which was produced by the bandgap voltage reference?
And how can I build a current mirror with the bandgap voltage reference to create the reference constant current? I want to build all in 0.18um CMOS technology.

 

[dick_freebird]

The bandgap at its heart -is- current mirrors -
jacked in a specific way, for effect.

You may not want an ideal-as-practical bandgap. The rolled-up drifts may want a nonzero TC to
compensate. PTAT, sure, but -what- proportionality?

That says you want to find "what makes it so" for the oscillator care-abouts.

If you have a reference voltage provided then a feedback unity gain buffer can get you "fixed"
currents using a FET follower with source resistance, Isink(t)=VREF(t)/RSET(t). Then mirrors and switches to get you up, down charging current at the timing cap.

Schmitt hysteresis band tends to be real sloppy as it's a 4-transistor tug-of-war with discrepant sizes, sometimes "history effects". A very not-great "reference" to hang the rest of it on. If you're going to the trouble of a true bandgap then you could do better for base reference stability.

 

[analog_design255]

The bandgap at its heart -is- current mirrors -
jacked in a specific way, for effect.

You may not want an ideal-as-practical bandgap. The rolled-up drifts may want a nonzero TC to
compensate. PTAT, sure, but -what- proportionality?

That says you want to find "what makes it so" for the oscillator care-abouts.

If you have a reference voltage provided then a feedback unity gain buffer can get you "fixed"
currents using a FET follower with source resistance, Isink(t)=VREF(t)/RSET(t). Then mirrors and switches to get you up, down charging current at the timing cap.

Schmitt hysteresis band tends to be real sloppy as it's a 4-transistor tug-of-war with discrepant sizes, sometimes "history effects". A very not-great "reference" to hang the rest of it on. If you're going to the trouble of a true bandgap then you could do better for base reference stability.

The goal is to achieve a frequency of 20MHz with a relative fault of 20%. My Professor means it works with a Schmitt Trigger and an inverter feedback path but I don’t know how many inverters I should use.
The Bandgap reference voltage is already designed but now I have to use this voltage to generate a constant current to charge and discharge the capacitor. I don’t know how to convert this voltage to a reference current and in which place I should include this current.
Are there any papers which discuss this topic?
I have attached the schematic of my designed Schmitt trigger.
Thank you for your help.