IrDA Receiver using discretes
I am designing discrete IrDA receiver using a TIA and a comparator. My initial circuit is given below. I won't be using a BPF after the TIA as given in the MAX3120 Functional block diagram. The output of comparator will be connected to the Microcontroller. For TIA the opamp used is OPA859-Q and the comparator is TLV7011. Positive reverse bias is provided for the photodiode.
My current source IG1 is a bit stream of 1010 (for IrDA '0' is represented as a pulse and '1' is represented by no pulse) with a speed of 115.2 Kbps.
The typical current of photodiode is 2.53 µA. Min is 1.37 µA and max is 3.8 µA
Bit period = 8.68 µS and pulse width for '0' is (3/16) * 8.68 µs = 1.63 µS. My input waveform is given below.
Input Signal
The complete response is given below.
May I know your thoughts about this circuit? Is this logically correct?
In complete response you see the output of TIA is between 2.05 V and 1.8 V. When PD current is zero am expecting 3V(Vref(V2)) at the output and current is high I am expecting 2.75 V at the output. Don't know why and how this difference is coming.
I am planning to make some modifications in this circuit. My plan is to put a difference amplifier at the output of TIA to remove the DC offset currently set by the 3 V connected to TIA's non inverting input. This will help enhance the voltage difference between high and low photodiode currents. After that, I'll add a non-inverting comparator with a hysteresis of around 100 mV to 200 mV for more reliable signal detection.
Kindly share your thoughts about the proposed modification in the existing circuit.
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