Chapter 7: FET Biasing

Transcription

1 Chapter 7: FET Biasing slamic University of Gaza r. Talal Skaik

2 Basic Current elationships For all FETs: G 0A S For JFETS and -Type MOSFETs: SS 1 P For E-Type MOSFETs: k( T ) Electronic evices and Circuit Theory, 10/e r. Talal Skaik 014

3 Fixed-Bias Configuration G 0A S 0,, S S GG SS 1 p Network for dc analysis. Electronic evices and Circuit Theory, 10/e 3 r. Talal Skaik 014

4 Fixed-Bias Configuration Graphical Solution SS 1 p Plotting Shockley s equation. Finding the solution for the fixed-bias configuration. Electronic evices and Circuit Theory, 10/e 4 r. Talal Skaik 014

5 Example 7.1 Find Q, Q, S,, G, S. Electronic evices and Circuit Theory, 10/e 5 r. Talal Skaik 014

6 Example graphical solution Electronic evices and Circuit Theory, 10/e 6 r. Talal Skaik 014

7 Self-Bias Configuration C analysis of the self-bias configuration. Electronic evices and Circuit Theory, 10/e 7 r. Talal Skaik 014

8 Self-Bias Configuration S SS 1 p SS 1 1 S SS 1 p By squaring and rearranging, has the form: k k 0 [Solve for ] p S C analysis of the self-bias configuration. Electronic evices and Circuit Theory, 10/e 8 r. Talal Skaik 014

9 Self-Bias Configuration graphical solution Sketch the transfer curve. raw the line: The Q-point is located where the line intersects the transfer curve. Use the value of at the Q- point ( Q ) to solve for the other voltages: ( ) S S S S S S S Electronic evices and Circuit Theory, 10/e 9 r. Talal Skaik 014

10 Example 7. Find Q, Q, S,, G, S. Solution raw the line: S Electronic evices and Circuit Theory, 10/e 10 r. Talal Skaik 014

11 Example 7. - solution Sketching the device characteristics for the JFET etermining the Q-point for the network. Electronic evices and Circuit Theory, 10/e 11 r. Talal Skaik 014

12 oltage-ivider Bias G = 0 A 1 = edrawn network for dc analysis. Electronic evices and Circuit Theory, 10/e 1 r. Talal Skaik 014

13 G is equal to the voltage across divider resistor : G 1 oltage-ivider Bias Using Kirchhoff s Law: G The Q point is established by plotting a line that intersects the transfer curve. S Electronic evices and Circuit Theory, 10/e 13 r. Talal Skaik 014

14 Step 1 Plot the line by plotting two points: = G, = 0 A = 0, = G / S Step Plot the transfer curve by plotting SS, P and the calculated values of Step 3 oltage-ivider Bias G S The Q-point is located where the line intersects the transfer curve Electronic evices and Circuit Theory, 10/e 14 r. Talal Skaik 014

15 oltage-ivider Bias G S Effect of S on the resulting Q-point. Electronic evices and Circuit Theory, 10/e 15 r. Talal Skaik 014

16 oltage-ivider Bias Using the value of at the Q-point, solve for the other variables in the voltage-divider bias circuit: S S S ( S ) 1 1 Electronic evices and Circuit Theory, 10/e 16 r. Talal Skaik 014

17 Example 7.5 Find Q, Q, S,, G, S. Electronic evices and Circuit Theory, 10/e 17 r. Talal Skaik 014

18 -Type MOSFET Bias Circuits epletion-type MOSFET bias circuits are similar to those used to bias JFETs. The only difference is that depletion-type MOSFETs can operate with positive values of and with values that exceed SS. Electronic evices and Circuit Theory, 10/e 18 r. Talal Skaik 014

19 Example 7.7 Find Q, Q, S Step 1 Plot the line for = G, = 0 A = G / S, = 0 Step Plot the transfer curve using SS, P and calculated values of. Step 3 The Q-point is located where the line intersects the transfer curve is. Use the at the Q-point to solve for the other variables in the voltage-divider bias circuit. G 1 These are the same steps used to analyze JFET voltage-divider bias circuits. G S Electronic evices and Circuit Theory, 10/e 19 r. Talal Skaik 014

20 For 1 Example Solution 1 SS 1 =6mA mA p 3 10 M (18 ) G (750) 10M 110M G 1 G S Electronic evices and Circuit Theory, 10/e 0 r. Talal Skaik 014

21 Example 7.9 Find Q, Q, To plot line : / S S For 6, ( 6) /.4k.5mA To plot transfer curve for =+: SS 1 =8m 1 1.5mA p 8 Electronic evices and Circuit Theory, 10/e 1 r. Talal Skaik 014

22 E-Type MOSFET Bias Circuits The transfer characteristic for the e-type MOSFET is very different from that of a simple JFET or the d-type MOSFET. k ( Th ) Electronic evices and Circuit Theory, 10/e r. Talal Skaik 014

23 Feedback Bias Circuit G = 0 A G = 0 S = = 3 C equivalent of the network Electronic evices and Circuit Theory, 10/e r. Talal Skaik 014

24 Step 1 Plot the line using =, = 0 A = /, = 0 Step Using values from the specification sheet, plot the transfer curve with Th, = 0 A (on), (on) Feedback Bias Q-Point Step 3 The Q-point is located where the line and the transfer curve intersect = Step 4 Using the value of at the Q- point, solve for the other variables in the bias circuit. Electronic evices and Circuit Theory, 10/e 4 r. Talal Skaik 014

25 Example 7.11 Plot Transfer Curve: Find Q, Q 3 k ( Th ) k k ( on ) ( on ) ( Th ) 6mA Electronic evices and Circuit Theory, 10/e 5 r. Talal Skaik 014

26 Example solution Plot the line : = = 1 (k) Electronic evices and Circuit Theory, 10/e 6 r. Talal Skaik 014

27 oltage-ivider Biasing Plot the line and the transfer curve to find the Q-point. Use these equations: G 1 S G S ( S ) Electronic evices and Circuit Theory, 10/e 7 r. Talal Skaik 014

28 Example 7.1 k k ( on ) ( on ) ( Th ) 3mA k ( Th ) Find Q, Q M (40 ) G M 18M G S (0.8 k ) Electronic evices and Circuit Theory, 10/e 8 r. Talal Skaik 014

29 Example Solution 18 (0.8 k ) Electronic evices and Circuit Theory, 10/e 9 r. Talal Skaik 014