AMP, ADC, Transistor Questions!

Started by Unknown May 8, 2016

Hello everyone.  I am picking up on a project someone else worked and and I wanted to see if anyone had some ideas on a amplifier and ADC connection that is being made in their schematic:

1.) See the schematic here:

2.) I am using a differenctial amplifier to measure a signal (U4 and U5 of schemiatc on link).

3.) There is a 2.0V reference (U2:9 -> VREF+) that is generated from my microcontroller that is used as the reference input for the amplifier output.

4.) The output of the amplifier (U4:6, U5:6) I would normally expect to go directly to the analog to digital converter (ADC) of my microcontroller but I see the output of the amplifer connecting to the emitter of a PNP transistor and then to the input of the analog to digital converter (ADC) of my microcontroller

5.) What is the purpuse of C11 and C13 on the outputs of U4 and U5?

6.) What would be the reason to use those transistors (Q1A and Q1B).  

7.) Will the transistorrs alawys be on with the base of Q1A and Q1B being connected directly to 3.3V?

8.) There is a note in the fireware that says that "We're wired so that 0v at the source -> 0 volts at conversion".  

How I am viewing this is that if there there is no difference on the input pins of the amplifier the output will be "zero" but then this will be on top of the refernce of 2V. (Using the refernce, pin 5) of the amplifer.  I guess I am missing something here and don't understand what the transistors are doing. Seems they would just pull the signal to ground
the entire time? If the source is 0V how would I have 0V at conversion?

Thank you.