Electronics Class Notes — Tutorial 8

Teacher: Prof P. M. Sarun • NPHC206 • WINTER - 2025-2026 • Last updated:

Questions

  1. A JFET has the following parameters: \(I_{\text{DSS}} = 32 \,\text{mA}\) ; \(V_{\text{P}} = – 8\,\text{V}\) ; \(V_{\text{GS}} = – 4.5 \,\text{V}\). Find the value of drain current.
  2. A JFET has a drain current of \(5 \,\text{mA}\). If \(I_{\text{DSS}} = 10 \,\text{mA}\) and \(V_{\text{GS (off)}} = – 6 \,\text{V}\), find the value of (i) \(V_{\text{GS}}\) and (ii) \(V_{\text{P}}\).
  3. Determine the value of drain current for the circuit.
    4. Tutorial 8
    Figure 1.
  4. What is the value of transconductance when \(V_{\text{GS}}\) of a JFET changes from \(–3.1 \,\text{V}\) to \(–3 \,\text{V}\), the drain current changes from \(1 \,\text{mA}\) to \(1.3 \,\text{mA}\).
  5. A JFET has a value of \(g_{\text{mo}} = 4000 \,\mu\text{S}\). Determine the value of \(g_{\text{m}}\) at \(V_{\text{GS}} = – 3\,\text{V}\). Given that \(V_{\text{GS (off)}} = – 8\,\text{V}\).
  6. For a certain D-MOSFET, \(I_{\text{DSS}} = 10 \,\text{mA}\) and \(V_{\text{GS (off)}} = – 8\,\text{V}\). (i) Determine the channel of the device. (ii) Calculate \(I_{\text{D}}\) at \(V_{\text{GS}} = -3\,\text{V}\) and \(I_{\text{D}}\) at \(V_{\text{GS}} = +3\,\text{V}\).
  7. The data sheet for an E-MOSFET gives \(I_{\text{D(on)}} = 500 \,\text{mA}\) at \(V_{\text{GS}} = 10\,\text{V}\) and \(V_{\text{GS (th)}} = 1\,\text{V}\). Determine the drain current for \(V_{\text{GS}} = 5\,\text{V}\).
  8. Determine \(I_{\text{DSS}}\) in a D-MOSFET. Given \(I_{\text{D}} = 3 \,\text{mA}\), \(V_{\text{GS}} = – 2\,\text{V}\) and \(V_{\text{GS (off)}} = – 10\,\text{V}\).
  9. How will you plot the transconductance curve for this E-MOSFET, when the The data sheet for an E-MOSFET gives \(I_{\text{D (on)}} = 3 \,\text{mA}\) at \(V_{\text{GS}} = 10\,\text{V}\) and \(V_{\text{GS (th)}} = 3\,\text{V}\).
  10. Sketch the transfer curve for a p-channel JFET with \(I_{\text{DSS}} = 4 \,\text{mA}\) and \(V_{\text{P}} = 3 \,\text{V}\).
  11. Determine \(V_{\text{DS}}\) for the circuit when \(I_{\text{DSS}} = 8 \,\text{mA}\).
    12. Tutorial 8
    Figure 2.
  12. Determine \(V_{\text{DS}}\) for the circuit when \(I_{\text{DSS}} = 10 \,\text{mA}\)
    13. Tutorial 8
    Figure 3.
  13. Find \(V_{\text{GS}}\) and \(V_{\text{DS}}\) in the JFET circuit shown in Fig. 4. Given, \(I_{\text{D}} = 1.9 \,\text{mA}\).
    14. Tutorial 8
    Figure 4.
  14. Draw the d.c. load line for the JFET amplifier as shown in Fig 5.
    15. Tutorial 8
    Figure 5.

Answers

  1. \(I_{\text{D}} = I_{\text{DSS}} \left[1-\frac{V_{\text{GS}}}{V_{\text{P}}}\right]^{2} = 6.12 \,\text{mA}\)
  2. \(V_{\text{GS}} = -1.76 \,\text{V}\)
  3. \(I_{\text{D}} = 1.33 \,\text{mA}\)
  4. \(g_{\text{fs}} = \frac{\Delta I_{\text{D}}}{\Delta V_{\text{GS}}} = 3 \,\text{mS}\)
  5. \(g_{\text{m}} = g_{\text{mo}} \left[1-\frac{V_{\text{GS}}}{V_{\text{GS (off)}}}\right] = 2.5 \,\text{mS}\)
  6. (i) n-channel; (ii). \(I_{\text{D}} =3.91 \,\text{mA}\) (iii) \(I_{\text{D}} =18.9 \,\text{mA}\)
  7. \(K = \frac{I_{\text{D (on)}}}{(V_{\text{GS (on)}}-V_{\text{GS (th)}})^{2}} = 6.17 \,\text{mA/V}^{2}\); \(I_{\text{D}} = 98.7 \,\text{mA}\)
  8. \(I_{\text{DSS}} = 4.69 \,\text{mA}\)
  9. Hint: Find \(K = 0.061 \times 10^{–3} \,\text{A/V}^{2}\); Find \(I_{\text{D}}\) for incremental \(V_{\text{GS}}\)
  10. Hint: \(I_{\text{D}} = I_{\text{DSS}} \left[1-\frac{V_{\text{GS}}}{V_{\text{P}}}\right]^{2}\)
  11. \(V_{\text{DS}} = 5.4\,\text{V}\)
  12. \(V_{\text{DS}} = -3.4 \,\text{V}\)
  13. \(V_{\text{GS}} = − 1.56\,\text{V}\); \(V_{\text{DS}} = 13.5\,\text{V}\)
  14. Find Operating point and Plot in \(I_{\text{D}}\) vs. \(V_{\text{DS}}\) graph

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