Re: HELP PLEASE
The classical approach is to create two current mirrors. These will charge and discharge a capacitor. Since the current is constant, the voltage across the capacitor will vary linearly. The comparators are used to detect the peak/ valley of the wavefor and switch on/ off each of the current mirrors.
A few examples are found here: **broken link removed**, although here you will find an opamp implements the current source.
Also here, all the sine approximation circuits first generate a triangle **broken link removed**