I'm having trouble thinking of a way to convert a negative voltage to a positive one with an inverting OPA. I have an input voltage range of [-5 to -1]V and I need to convert it into a positive voltage to compare it with a reference voltage ( regulation for my charge pump) and I only have a positive supply voltage of 5V.

I studied the one stage OTA shown below and the minimum input voltage is \[ V_{icmin} = V_{gs1} + \frac{V_{g5}-V_{th5}}{n_{5}} \] So I can't have a negative input in my OTA.

I was wondering if there is a way to be able to use the OTA for a negative input voltage or if there is another way to convert it into a positive voltage where I won't be needing a regulation.

Thank you