hi all, I am in trouble making an analog signal amplifier using a configuration from someone's previous post. here is the carrier signal split where positive and negative signal shifted 180 degree then i check the output of both opamp and there is no problem but if the opamp output is put in to the mosfet there is no gain at the mosfet output. is there anything I miss?

 

R5 decreasing to 33K or R6 increasing to 330K.
If it still doesn't works then exchange the input(-) and (+) of two op amp and try again.

 

What is the intent of the circuit?
What are the voltage scales of the two scope shots?

ak

 

The gate voltage isn't high enough to turn on the FET. It needs Vgs=10V to turn on fully, and as much as 4V just to turn on enough to pass a few uA.

 

R5 decreasing to 33K or R6 increasing to 330K.
If it still doesn't works then exchange the input(-) and (+) of two op amp and try again.

i change the resistor value the output both opamp become unbalance, i repeat it for acceptable scope signal but dead zone increase between channel A & B

 

The gate voltage isn't high enough to turn on the FET. It needs Vgs=10V to turn on fully, and as much as 4V just to turn on enough to pass a few uA.

i have supply up to 30v +/- should i rise the supply peak voltage? i know Vgs gate need 10V minimum the sine signal above is actualy amplitude modulation i want to drive Vgs rise from 5V to 10V then back down, would that shaping Vds also?

 

i want to drive Vgs rise from 5V to 10V then back down, would that shaping Vds also?

If Vgs(thr) is <5V the FET would be permanently turned on. Your FET stage is not configured as a linear amplifier, if that is what you want.

 

If Vgs(thr) is <5V the FET would be permanently turned on. Your FET stage is not configured as a linear amplifier, if that is what you want.

yes exactly, after read irfz44n datasheet there is no possibility to shaping VDS even low pass filter applied. im trying to figure it out how to drive AM transmitter by split single sine signal, both opamp are has nice balanced positive and negative swing with no dead zone between them. do you have suggestion?

 

Can you post a schematic of the transmitter?
SG