LIC–Analog Multiplier and PLL (Unit 3)–2 Marks with Anwers

Anna University





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,

Kv= fo / Vc = 8fo /Vcc

where, ∆Vc is the modulation voltage required to produce the frequency shift ∆fo

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.

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