Solving Op Amp Confusion with PWM Circuit

[jafferrox]

Hi

In the waveform picture i attached, I don't know why the square wave is floating instead of being on the 0 of the x axis. I also attached schematic of the pwm circuit.

By the way, this is a pulse width modulator circuit made of 4 op amps, U2D is a schmitt trigger to generate sqaure wave, U2C is integrator that integrates square and generate triangle wave, U2A is comparator which is used to generate PWM signal and U2B is used to isolate pwm signal from the load that's going to connect to the output.

Thanks in advance

 

[skeptic2]

The design of the opamp prevents the output from going all the way to the negative supply or all the way to the positive supply. There are other opamps, often called "rail-to-rail, with which the outputs do go to the positive and negative supplies.

 

[NascentOxygen]

You could add a simple 1 or 2 FET buffer stage to cause that signal to hit ground, if that were important.

 

[jafferrox]

thanks for the help guys.