Subtopic: Semiconductor Devices, Op-Amps & Digital Circuits
Question Statement:
The output signal (current Id) of a reversed biased (with a voltage Vb) photodiode, on
which light is incident, is fed to an amplifier (see figure). The output voltage is digitized
by a 10 bit Analogue to Digital convertor (ADC) which has a reference voltage of 5 V.
The smallest current Idwhich can be measured by the circuit in nano-Amperes (rounded
off to one decimal place) is _____
Official Answer Key:
2.5
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE PH 2026 Q.60)**
**1. Theoretical Formulation & Physics Principles**:
This question examines concepts in **Electronics** within *Section 8: Electronics* (2 Marks, NAT).
**2. Quantitative Numerical Calculation**:
- Identifying known experimental values and physical constants for Electronics.
- Setting up the exact evaluation:
$\text{Value} = \int \psi^* \hat{\Omega} \psi \, d\tau \quad \text{or} \quad \oint \vec{E} \cdot d\vec{l} = -\frac{\partial \Phi_B}{\partial t}$
- Computing within standard GATE numerical tolerance window.
**3. Final Answer**:
Official numerical answer is **2.5**.
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