Mirror Current Source Circuits
 |
| 8.13 Find the voltages at all nodes and the currents through all branches in the circuit of Fig. P8.13. Assume VBE =0.7 V and β = ∞ |
 |
 |
| 8.84 Consider the Wilson current-mirror circuit of Fig. 8.40
when supplied with a reference current IREF of 1 mA.
What is the change in IO corresponding to a change of
+10 V in the voltage at the collector of Q3? Give both the
absolute value and the percentage change. Let β = 100 and
VA = 100 V |
 |
| D 8.85 (a) The circuit in Fig. P8.85 is a modified version of
the Wilson current mirror. Here the output transistor is “split” into two matched transistors, Q3 and Q4. Find IO1 and IO2 in terms of IREF. Assume all transistors to be matched with current gain β. (b) Use this idea to design a circuit that generates currents of 0.1 mA, 0.2 mA, and 0.4 mA, using a reference current source of 0.7 mA. What are the actual values of the currents generated for β = 50 |
 |
D 8.90 (a) Utilizing a reference current of 200 μA, design a Widlar current source to provide an output current of 20 μA. Assume β to be high. (b) If β = 200 and VA = 50 V, find the value of the output resistance, and find the change in output current corresponding to a 5-V change in output voltage |
 |
each having a 100-μA reference current: one with a current transfer ratio of 0.8, one with a ratio of 0.10, and one with a ratio of 0.01, all assuming high β. For each, find the output resistance, and contrast it with ro of the basic unity-ratio source that is providing the desired current and for which RE = 0. Use β = ∞ and VA = 50 V |
 |
| B) D 8.91 Design three Widlar current sources, |
 |
| D 8.92 (a) For the circuit in Fig. P8.92, assume BJTs with high β and vBE = 0.7 V at 1 mA. Find the value of R that will result in IO = 10 μA. (b) For the design in (a), find Ro assuming β = 100 and VA = 40 V |