JFET Ohmic Resistance Calculation
This question asks us to find the ohmic resistance of a JFET (Junction Field-Effect Transistor) given specific parameters: the pinch-off voltage, denoted as \(V_p\), and the drain current when the channel is fully on (zero gate-source voltage and saturation), denoted as \(I_{DSS}\).
Understanding JFET Ohmic Resistance
The ohmic resistance (or zero-bias resistance) of a JFET is typically the resistance between the drain and source terminals when the device is operating in the linear (or triode) region with zero gate-source voltage (\(V_{GS} = 0\)). This is often referred to as \(R_{DS(on)}\) when \(V_{GS}=0\).
A common approximation used to estimate this resistance relates the pinch-off voltage and the saturation drain current.
Formula for Ohmic Resistance
The formula used for calculating the approximate ohmic resistance (\(R_{DS(on)}\)) when \(V_{GS} = 0\) is:
$ R_{DS(on)} \approx \frac{V_p}{I_{DSS}} $- \(V_p\) is the pinch-off voltage.
- \(I_{DSS}\) is the drain current when \(V_{GS} = 0\) and the JFET is in saturation.
Applying the Formula
We are given the following values:
- Pinch-off Voltage, \(V_p = 4V\)
- Drain Current at Saturation (\(V_{GS}=0\)), \(I_{DSS} = 10mA\)
First, ensure the current is in Amperes:
$ I_{DSS} = 10mA = 10 \times 10^{-3} A = 0.01 A $Now, substitute these values into the formula:
$ R_{DS(on)} \approx \frac{4V}{0.01 A} $Performing the calculation:
$ R_{DS(on)} \approx 400 \ \Omega $Result
Therefore, the ohmic resistance of the JFET under these conditions is approximately 400 Ohms.
Important Questions from Operation of JFET
A junction Field Effect Transistor can operate in
In a junction field effect transistor the depletion layer width at a distance x from the source is:
Which of the following statements are correct for an N channel FETs?
A. N channel FET has larger electron mobility than P channel FETs.
B. N channel FET has electrons as current carriers.
C. N channel FET has more noise than P channel FET.
D. N channel FET has larger transconductance than P channel FETs.
Choose the correct answer from the options given below:For a JFET, above the pinch-off voltage, as the drain voltage increases, the
List – I (Structure/Characteristics) List – II (Reasons) a. n-channel JFET is better than p-channel JFET i. Reverse bias increases along the channel b. Channel is wedge shaped ii. High electric field near the drain and directed towards source c. Channel is not completely closed at pinch-off iii. Low leakage current at the gate terminal d. Input impedance is high iv. Better frequency performance since μn >> μp Codes :
