Question

In the block diagram of a simple modulator for obtaining an AM signal, shown in the figure, identify the boxes A and B. Write their functions.

Answer 1

Boxes ‘A’ and ‘B’ represents 

(i) square law device 

(ii) band pass filter 

(i) Square law device is a non linear device and produces the output 

y(t) =Bx (t) +Cx(t)² 

where B and C are constants. 

(ii) It rejects dc and sinusoids of frequencies ω_m, 2ω_m and 2ω_c and finally produces amplitude modulated wave by retaining frequncies ω_c, ω_c – ω_m and ω_c + ω_m.