if this schematic is correct, then I think it is like a (sensor + pre-amp+ amp ) ckt.
maybe the left part is a CMOS sensor, the pre-amp will amplify that sensor signal, then the inverter (amp or comparator) make this signal to logic level. the rightmost part is biasing ckt (but quite strage) for the sensor.....
Try to understand the function of this circuit in its application, and that will make it clearer and easier to understand the purpose of this circuit, i think.