Assignment and Solutions on Current Mirrors

All  Problems in Single file : [PDF]     [Solutions]

1. Design a simple current mirror using a current of 1 μA and V_GS of 1 volt.
2. Design a circuit to bias the MOSFET in figure shown, so that its drain current is 5 μA. Estimate the minimum voltage across M1 if it is to remain in saturation.
   
3.  Determine the current that flows in M3 of  figure shown. Neglect oxide encroachment and the finite output resistance of the M3.
   
4.  Determine the currents that flow in figure shown, if the size of M2 is 30/5. Compare the results with above problem and write your observations.
   
5.  Determine the ac currents that comes from  source v_t. Assume λ = 0.06 per volt.
   
6.  Design a bias circuit so that the current that flows in M1 and M2 is 1μA. What are the small signal resistances looking into the drains of M2 and M1 ? what is the minimum voltage across M1 and M2 for operation in the saturation region ?
   
7.  Using small signal analysis, prove that the resistance looking into drain of figure shown is
   
8. For the circuit shown below, design current sources with output currents of 10 μA and 15 μA. Estimate the minimum voltage across the current sources and the output resistance. What is the V_SG of the 100/5 MOSFET that sources 10 μA current ?
   
9.  Estimate the variation in I_o for the simple current mirror shown below, for V_SS changing from -2.4 volts to -2.6 volts.
   
10. Assume that a threshold voltage difference of 10 mV exists between the two MOSFETs used in a simple current mirror made using equal size MOSFETs. Calculate the difference in the drain currents to change with the MOSFET V_GS ? Is matching between the currents better or worse with large V_GS ? what happens to the minimum voltage across the current mirror if V_GS is increased ?
11.  Using the Wilson current mirror shown in figure and the CN 20 process, design a mirror in which I_o = 150 μA with I _REF = 50 μA for V_DD = 5 volts, V_SS = 0 volts.           
    
12. A Wilson current mirror is designed with V_DD = 5 volts, V_SS = 0 volts, I_REF = 10 μA and all devices sized to 10 μm / 10 μm.                                                                                                                   a. calculate the value of the small signal output resistance of the Wilson current mirror.                                                                                                                                             b. calculate the minimum output voltage, V_omin.                                                                                  c. Layout the devices M4 through M7, assuming that each device is 40/5 using an interditigated layout technique to match devices M5 and M6. Use parallel devices for M4 and M7.
    

   13.  For a cascode current mirror made using 15/5 devices,   
          a. calculate the value of the small signal output resistance of the Wilson current  

            mirror.                 
         b. calculate the minimum output voltage, V_omin.

   14.  Design a regulated cascode current sink of 1 μA. Estimate the output resistance of the current sink.
   15.  The basic idea used in the regulated cascode current sink is shown below.

 

What is the output resistance of this configuration? show that if the gain A is gm(ro/2), then the output resistance of the configuration reduces to  

  16.  Consider the schematic of the modified current mirror shown below. Estimate the small signal resistance to ground at both nodes A and B. if a resistor is used to connect node A to V_DD, write an equation relating the drain currents of M1 and M2 to the resistor value.