**Anna University**

**Q****UE****STION BANK ANSWERS (2 MARKS)**

**147404 - LINEAR INTEGRATED CIRCUITS**

**UNIT III **

**ANALOG MULTIPLIER AND PLL**

**1. List out the blocks of PLL.**

a. Phase detector/comparator

b. Low pass filter

c. Error amplifier

d. Voltage controlled oscillator

**2. Define the following terms related to PLL, a) Capture range**

The range of frequencies over which the PLL can acquire lock with an input signal is called the capture range. It

is expressed as a percentage of the VCO free running frequency.

**b) Lock range**

The range of frequencies over which the PLL can maintain lock with the incoming signal is called the lock-in range or tracking range. It is expressed as a percentage of the VCO free running frequency.

**3. Write the expression of a) capture range**

**b) lock range**

Lock in range ∆fL = +/- 7.8 fo / V

fo is free running frequency

Capture range = +/- = [∆fL / (2*∏*R*C)] 1/2

**4. Define voltage to frequency conversion factor of VCO.**

Voltage to Frequency conversion factor is defined as,

**K****v****= **∆**f****o ****/ **∆**V****c ****= 8fo /Vcc**

where, ∆**V****c ****i****s **the modulation voltage required to produce the frequency shift ∆**f****o **

**5. Mention the applications of analog multipliers.**

1. Voltage squarer

2. Frequency doubler

3. Voltage divider

4. Square rooter

5. Phase angle detector

6. Rectifier

**6. List out the applications of PLL.**

a. Frequency multiplication/division

b. Frequency translation c. AM detection

d. FM demodulation

e. FSK demodulation.

**7. Define phase transfer conversion coefficient of PLL.**

The covertion ratio Kd of phase detector is given by

Kd = Vcc/π

**8. Briefly write on frequency synthesizers.**

A frequency synthesizer is an electronic system for generating any of a range of frequencies from a single fixed time base or oscillator. They are found in many modern devices, including radio receivers, mobile telephones, radiotelephones, walkie-talkies, CB radios, satellite receivers, GPS systems, etc. A frequency synthesizer can combine frequency multiplication, frequency division, and frequency mixing (the frequency mixing process generates sum and difference frequencies) operations to produce the desired output signal.

**9. Explain how a frequency doubler can be realized using analog multiplier.**

The multiplication of two sine waves of the same frequency, but of possibly different amplitudes and phase allows doubling a frequency using an analog multiplier.

**10. What is a compander IC?**

The term companding means compressing and expanding. In a communication system, the audio signal is compressed in the transmitter and expanded in the receiver. Examples: LM 2704- LM 2707; NE 570/571.

**11. What is a peak detector?**

A *peak detector *is a series connection of a diode and a capacitor outputting a DC voltage equal to the peak value of the applied AC signal.