Section A
Q1.
(a) (i) An InGaAs photodiode operating at 1.3 mu m is limited by background radiation giving I_B = 10^{-7} A. The responsivity of the diode is 0.74 A/W at 1.3 µm. Find the minimum detectable power of this photodiode if the bandwidth of the device is 10 MHz and load resistance is R_L = 107 Omega.
(a) (ii) An nMOS transistor has a threshold voltage (Vt) of 0.4 V and a supply voltage V_{DD} = 1.2 V. A circuit designer is evaluating a proposal to reduce Vt by 100 mV to obtain faster transistor. By what factor would the subthreshold leakage current increase at room temperature at V_{gs} = 0? Assume n = 1.4.
(b) Design a two-sided limiting circuit using a resistor, two diodes and two power supplies to feed a 1 kOmega load with nominal limiting levels of pm 3 V. Use voltage drop of 0.7 V for each diode when conducting. In the non-limiting region, the circuit voltage gain should be at least 0.95 V/V.
(c)
Find the node voltages Va and Vb for the circuit shown in the figure using node voltage analysis. Also, find the current through 5 Omega resistor : ```json
{ "circuit": [ {"component": "resistor", "value": "5 Ohm", "nodes": ["Va", "ground"]}, {"component": "current source", "value": "1 A", "direction": "up", "nodes": ["ground", "node1"]}, {"component": "resistor", "value": "2 Ohm", "nodes": ["node1", "Va"]}, {"component": "resistor", "value": "5 Ohm", "nodes": ["node1", "Vb"]}, {"component": "current source", "value": "2 A", "direction": "clockwise", "nodes": ["Va", "Vb"]}, {"component": "resistor", "value": "10 Ohm", "nodes": ["Vb", "ground"]}, {"component": "resistor", "value": "4 Ohm", "nodes": ["Vb", "ground"]}, {"component": "current source", "value": "3 A", "direction": "up", "nodes": ["ground", "Vb"]}, {"component": "resistor", "value": "2 Ohm", "nodes": ["node1", "ground"]} ]
}
```
