mailkit
Newbie level 4
Hi
I am designing a common source amplifier and I am using a POWER MOSFET (2N7269). I am using a voltage divider biasing. My input is of 5Vpp (ac) and I require a tunable gain of 0 - 5. The circuit can be seen on:
http://www.geocities.com/alok_garg_4u/common_source_amp.htm
Well I have done the calculations and according to the requirements and the output plot of 2N7269 I get the values as:
Id = 10amp
Vgs = 4.694V
Vds = 11V
Vdd = 24V
Further calculations show that
Rd + Rs = (Vdd - Vds)/Id = 1.3ohms (Rd is drain R and Rs is source R)
gm = sqrt{ 2*Id*K*(W/L)*[1+(lambda)*Vds] } = 32.4369
rd = (1+(lambda)*Vds)/(lambda)*Id = 28.3908
Now as I require a gain of 5, I have:
Avi = gm (Rd in parallel with rd)
And from above formula I get value of Rd as .1549ohms for Avi as 5 and .47ohms for Avi as 15.
Now we can see that the value of Rd and Rs is very small and all this will make the circuit very bulky. Now as I need a tunable amplifier, I need to change the value of Rd for different gain.
Well what I require is if one can help me with a better designing technique or if someone can suggest me a solution to my circuit.
Kindly help
Thanks
I am designing a common source amplifier and I am using a POWER MOSFET (2N7269). I am using a voltage divider biasing. My input is of 5Vpp (ac) and I require a tunable gain of 0 - 5. The circuit can be seen on:
http://www.geocities.com/alok_garg_4u/common_source_amp.htm
Well I have done the calculations and according to the requirements and the output plot of 2N7269 I get the values as:
Id = 10amp
Vgs = 4.694V
Vds = 11V
Vdd = 24V
Further calculations show that
Rd + Rs = (Vdd - Vds)/Id = 1.3ohms (Rd is drain R and Rs is source R)
gm = sqrt{ 2*Id*K*(W/L)*[1+(lambda)*Vds] } = 32.4369
rd = (1+(lambda)*Vds)/(lambda)*Id = 28.3908
Now as I require a gain of 5, I have:
Avi = gm (Rd in parallel with rd)
And from above formula I get value of Rd as .1549ohms for Avi as 5 and .47ohms for Avi as 15.
Now we can see that the value of Rd and Rs is very small and all this will make the circuit very bulky. Now as I need a tunable amplifier, I need to change the value of Rd for different gain.
Well what I require is if one can help me with a better designing technique or if someone can suggest me a solution to my circuit.
Kindly help
Thanks
