I'm trying to design the receiver circuitry for an IR link that detects 1MHz signals at least 70cm away. Currently I'm using an Optek photodiode (OP999) with OPA380 as my transimpedance amplifier, an op- amp after the transimpedance amp to further amplify the voltage and a comparator to reconstruct the transmitted signal. At the moment I'm just pulsing a 1MHz square wave through my IR emitter but the output from the transimpedance amplifier does not come out square! Can anyone suggest an IC transimpedance amp that will work for 1MHz signals across an IR link? (the OPA380 has a 1MHz bandwidth - hence the distortion at the output). Also, using just the OPA380 with a capacitor (to remove the varying offset) and a low pass filter I can meet the 70cm requirement. However with the op-amp and the comparator, I can only get about 20cm (if even that). Am I missing some fundamental component that is ultimately causing my receiver to fail?
Any help would be greatly appreciated!!