Difference between LDO and opamp

Hi,

I have some basic questions regarding LDO and opamp based amplifiers:

1. When is a LDO used and why can't an opamp based amplifier be used? For e.g. I came across a sensor analog front end system. A bandgap was designed to generate a reference voltage of ~1.2V. But the ADC needed a 2.4V reference so a LDO was designed with the bandgap as its reference. My question is: Why was a LDO designed and not a non-inverting/inverting opamp amplifier?

2. In the same sensor analog front end, another reference was designed for the digital blocks. The reference was ~1.2V. Here also, a LDO was designed with the bandgap as it's reference. My question is why wasn't a buffer opamp used instead?

Could someone please help me understand why?

Thanks!!

1. The LDO was probably simpler and used less chip space then an op amp.

2. See answer to 1.