8.2.2.2 Detailed Design Procedure

The IR receiver AFE design is highly streamlined and optimized. R₁ converts the IR light energy induced current into voltage and applies to the inverting input of the comparator. Because a reverse biased IR LED is used as the IR receiver, a higher I/V transimpedance gain is required to boost the amplitude of reduced current. A 10M resistor is used as R₁ to support a 1-V, 100-nA transimpedance gain. This is made possible with the picoamps Input bias current I_B (5pA typical). The RC network of R₂ and C₁ establishes a reference voltage V_ref which tracks the mean amplitude of the IR signal. The RC constant of R₂ and C₁ (about 4.7 ms) is chosen for V_ref to track the received IR current fluctuation but not the actual data bit stream. The noninverting input is connected to V_ref and the output over the R₃ and R₄ resistor network which provides additional hysteresis for improved guard against spurious toggles.

To reduce the current drain from the coin cell battery, data transmission must be short and infrequent.