Electronic Devices - BJT and FET Frequency Response - Discussion
Discussion Forum : BJT and FET Frequency Response - General Questions (Q.No. 4)
4.
Determine the lower cutoff frequency of this network.
Discussion:
11 comments Page 1 of 2.
Erwin John said:
6 years ago
@John.
For gm, get the value of current Id first. Use the formula:
Id = Idss (1- (Vgs/Vp))^2 but replace Vgs with -Id(Rs).
Then you will get two values of Id. Choose the lower value which is equal to 2mA.
The lower value of Id means that the FET is operating below the zero bias current, Idss.
Get Vgs using the formula Vgs = -Id(Rs).
And use this formula to get gm.
gm = (2Idss/|Vp|)(1-(Vgs/Vp)).
For gm, get the value of current Id first. Use the formula:
Id = Idss (1- (Vgs/Vp))^2 but replace Vgs with -Id(Rs).
Then you will get two values of Id. Choose the lower value which is equal to 2mA.
The lower value of Id means that the FET is operating below the zero bias current, Idss.
Get Vgs using the formula Vgs = -Id(Rs).
And use this formula to get gm.
gm = (2Idss/|Vp|)(1-(Vgs/Vp)).
Cleokaze said:
5 years ago
I still don't understand.
The largest of three cutoff frequencies are 159154.9431Hz which is near the input coupling capacitor. Then why did we choose the 238.73Hz? Please explain in detail.
The largest of three cutoff frequencies are 159154.9431Hz which is near the input coupling capacitor. Then why did we choose the 238.73Hz? Please explain in detail.
Kimi said:
4 years ago
Choose Rs and Cs because that is for Low-pass.
And based on the question we need a Low cut-off frequency. so the formula must be 1/(2*π*RC) wherein R=(Rs||(1/gm)).
And based on the question we need a Low cut-off frequency. so the formula must be 1/(2*π*RC) wherein R=(Rs||(1/gm)).
(1)
Abdul haseeb said:
6 years ago
How to calculate voltage gain, z input impedance and output impedance?
Kweku said:
7 years ago
@Pulls.
The formula gives D as answer when RG is taken as 1M ohms.
The formula gives D as answer when RG is taken as 1M ohms.
Paul said:
7 years ago
f=1/2π*Req*Cs.
where:
Req= Rs II 1/gm.
Ans. 238.73.
where:
Req= Rs II 1/gm.
Ans. 238.73.
Paul said:
7 years ago
The cut off frequency at Cs.
f=1/2π*(Rs II 1/gm)*Cs.
f=1/2π*(Rs II 1/gm)*Cs.
Pulls said:
1 decade ago
f = 1/2*pi*(rsi+rg)*cg formula can be used.
Abdul haseeb said:
6 years ago
How to calculate gm, Vgs, Id? Explain.
John said:
7 years ago
What's the value of gm?
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