Memory-based **analog**-based questions that appeared in **Texas Instruments Interview**. Try to solve similar kinds of questions in order to excel in your preparation level. The parameter values given in the questions to design may be different.

1. What should be the value of **Zs** that will transfer **maximum power** to the ZL? **R=50 Ohms and L=5H.**

**Options**

1. 50-jw5 Ohms

2. 50 Ohms

3. 60+jw5 Ohms

4. 0 Ohms

2. The **Op-amp** in the circuit shown below is **an ideal op-amp**. What is the **output impedance Zout**? if **Rs=100 Ohms.**

**Options**

1. 0 Ohms

2. 0.010 Ohms

3. 100 Ohms

4. Infinity

3. **Op-amp** in the below circuit is ideal. A **sine wave of frequency 1mrad/s** and **amplitude of 1V** is applied at **Vin.** What is the amplitude at node Vout? If **R =100 Ohm, C=1nF, R’=500 Ohm.**

**Options**

1. 6.0

2. 0.2

3. 2.0

4. 1.4

4. **V1** is a **non-ideal voltage source** whose output voltage is measured to be **Voc** when no load is connected to its output. **I1** is **an ideal current source**, which when **shorted** to ground forces a current of **Isc** through the short circuit.

The **output impedance of V1 is 1kOhm** and the **output impedance of I1 is 9kOhm**. If **V1** and **I1** are connected as shown below, what is the **node voltage at node Vx** (in volts). If **Isc=50mA, Voc=5v.**

**Options**

1. 49.50

2. 5.00

3. 0.00

4. 40.50

5. In the circuit shown below, **VCC** is connected to **3V. VIN** and **VINZ** are **complementary square wave** signals with a high level of **3volt** and a low level of **0volt.**

A voltage step from **3volt to 0volt** is applied at **VIN** (with the corresponding step from 0v to 3v applied at **VINZ)** at a time instant t=0. What is the time instant when the voltage at **VOUT** reaches **0.1v? If I=1mA, C=1pF, R=400 Ohm.**

**Options**

1. 40*ln(10) ns

2. 40ns

3. 40*ln(4) ns

4. 0.30ns

6. In the circuit shown below, the **capacitor** is **initially** charged to **5v**. The **diodes** shown are **ideal** with a **forward drop of 1V when ON.** Which of the following statements is **true** about the **voltage** waveform across the **capacitor?**

**Options**

1. It will remain at 5v

2. It will oscillate forever as a perfect sine wave

3. It will oscillate initially but then die down

4. It will oscillate forever but there will be voltage steps at the zero crossings

7. A **capacitor** used in the **process technology** has a symbol as **shown in (a)** and an **equivalent** representation as **shown in (b)** when connected between terminals 1 and 2.

**Two capacitors** are used in a circuit as **shown in (c)**. What is the **3db bandwidth** of the circuit between **Vin(t) and Vo(t)?** Assume that the **buffer** is **ideal.** Given **C = 1 mF.**

**Options**

1. 11 Krad/s

2. 24 Krad/s

3. 10 Krad/s

4. 909 Krad/s

8. For the circuit shown in the figure, what value of **L (Inductor)** will make the magnitude of **V1 and V2 equal** for all the **frequencies?** If **C = 2 micro Farad**, and **R = 4 ohm**.

**Options**

1. 16 micro Henry

2. 32 micro Henry

3. 5 micro Henry

4. 1 micro Henry

9. An **ideal op-amp** is used as a **digital buffer** as shown below. If the **rise time at Vin(t) is 1ns**, then the rise at **Vo(t)?**

**Options**

1. 0

2. 1ns

3. Depends on the value of C

4. You cannot use the Op-amp as the digital buffer.

10. A schematic of a **buck converter** is shown below. **Vin is the DC input voltage**. **CTRL** is a control signal that **periodically switches ON and OFF**. The control loop looks at the output voltage **Vo** and adjusts the **duty cycle of CTRL** to change **Vo** to the desired voltage. If **Vo** is to be set to **6v,** the value of **R** is gradually **increased.**

What is the **lowest value of R** at which the **inductor** current **touches 0** during the **transient?**

Assume that the **current** through the **inductor** is always higher than **0**. Also assume that the **capacitor** is **large** enough that **Vo** is almost **constant** and the **switching frequency of CTRL is 1 MHz and L = 1 mH, Vin = 10v.**

**Options**

1. 50 kOhm

2. 500 kOhm

3. 500 Ohm

4. 5 kOhm

11. An **amplifier** has a **non-linear** response given by **Vo = Vin + Vin^3** at all frequencies. When a **sine wave of amplitude 1v** is input to the amplifier, the output of the amplifier contains a **harmonic at -80 dBm**.

The amplifier output goes to a **low pass filter with a 3db BW of 1MHz**. What is the approximate **amplitude of the harmonic** at the output of the low pass filter if the input to the amplifier is a **3.33 MHz sine wave with an amplitude of 0.5v**?

**Options**

1. -98 dB

2. -78 dB

3. -106 dB

4. -118 dB

12. A **CMOS** (Complementary Metal Oxide Semiconductor) inverter runs off a **3v** supply (with the ground at 0v) and is loaded in three different ways as shown in fig (a),(b), and (c) below.

In (a), it is seen that the logic high level is **2.5v.**

In (b), it is seen that the logic low level is **0.5v.**

What is the expected l**ogic high level in (c)**?

**Options**

1. 3v

2. 57v

3. 5v

4. 75v

13. In the below diagram, **VCC is a 3V supply**. The block marked as **“Digital”** contains the digital running of the supply node marked as **DVDD.** For the purpose of estimating switching current, the digital block can be approximated as a **capacitor 10 pF switching ON and OFF** at the **clock frequency** (ON for half the period and OFF for the other half of the period).

The capacitor **CDECAP** is a **decoupling capacitor** with a value equal to **1000 pF** and is used to **smoothen** the **current ripple from VCC** that is **caused** because of the digital block **switching.** If the resistor **R is equal to 100 Ohm** and the **clock frequency** for the digital block is **1 GHz**, What is the value of **DVDD?**

**Options**

1. 5 Volts

2. 5 Volts

3. 3 Volts

4. 0 Volts

14. In the circuit below, the block marked as **buffer** provides a **gain of 2** between its input and output. The Op-amp is an **ideal Op-amp**. The circuit is excited using an input waveform **Vin(t) = 3 u(t)**.

The value of the resistor **R is 1.5 Ohm** and the value of the **capacitance C is 1 F**. The **lowest** voltage reached by **Vo(t)** is equal to:

**Options**

1. -6 Volts

2. 0 Volts

3. -3 Volts

4. -4.5 Volts

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