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[SOLVED] Non-linear amplifier for modulation

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danish.umer.k

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Hello Guys,
I have been given an assignment to design a Double side-band suppressed carrier modulator using non-linear amplifier method as shown in the attached figure. For this scheme to work I need a non linear amplifier whose output profile is y=a*x+b*x^2, where y is output and x is input. I have no idea how to design an amplifier that would have output given by such 2nd degree polynomial.
I have some understanding that usually in the design of amplifier we bias the transistor in a such a region that their output is almost linear; similarly we can bias it for this non-linear case but i need some help with this.
 

chuckey said:
Have you tried biassing the transistor right back (Ic= 2 micro A) and driving its base from a low impedance source?
Frank
Click to expand...
Sir it would be very helpful if you could explain it some more
 

For a non-linear amplifier, get the circuit of a class A voltage amplifier, reduce the voltage on the base by reducing the value of the lower base to earth resistor until the collector current is 2 micro amps - check the voltage drop across the collector load resistor. For any reasonable level of signal this amplifier is non-linear now. Does it do what you want?
Frank
 
chuckey said:
For a non-linear amplifier, get the circuit of a class A voltage amplifier, reduce the voltage on the base by reducing the value of the lower base to earth resistor until the collector current is 2 micro amps - check the voltage drop across the collector load resistor. For any reasonable level of signal this amplifier is non-linear now. Does it do what you want?
Frank
Click to expand...

Thanks a lot for your help. I however went for another alternative i made a logarithmic amplifier using op amp and suppressed the unwanted harmonics using filters and it worked for me.
 

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