![• Advantages
• Cascode current mirror eliminates the channel length modulation effect by
keeping Vds1 = Vds2 constant in the ratio
• Iout = [(W/L) (1+λVds2 )/(W/L) (1+λVds1)]Iref.
• Improves output resistance
• Disadvantages
• Less accurate.
• Current becomes constant for quite large value of Vds e.g. in this case
minimum Vds is 1.2 V.
• Body effect is also present which disturbs the output current.](https://image.slidesharecdn.com/ushaaaicdppt-150527155020-lva1-app6891/85/Design-of-optimum-self-cascode-low-voltage-current-mirror-10-320.jpg)
Design of optimum self cascode low voltage current mirror
- 1. Optimal High Performance Self Cascode CMOS Current Mirror BY USHASWINI CHOWDARY.M
- 2. Introduction • To meet the needs of present era of low power portable electronic equipment, many low voltage innovative design techniques like Self cascode CMOS Current Mirror. • In this paper, we have investigated the merits and demerits of various current mirror configurations.
- 3. • Then improved our results by using various configurations like cascode current mirror, Wilson current mirror and finally the current mirror based on self cascode CMOS. • The analysis is done using 0.18um cadence virtuoso environment.
- 4. Basic Mosfet current mirror
- 5. Limitations 1. As we can see from the basic current mirror circuit current gain is poor and the output current is having the channel length modulation effects. 2. Output resistance is finite and small value.
- 7. 7 CASCODE CURRENT MIRROR • The idea of cascode structure is employed to increase the output resistance (Fig.3) and the implementation requires NMOS technology. • It is used to remove the drawback of channel length modulation in basic current mirror. • In the simulation results of basic current mirror the channel length modulation effect was not considered.
- 8. • In practice, this effect results in significant error in copying currents. The circuit features a wide output voltage swing and requires an input voltage of approximately one diode drop plus a saturation voltage. • By maintaining the input transistors in saturation, the output current will track the input current, regardless of increases in ambient temperature
- 10. • Advantages • Cascode current mirror eliminates the channel length modulation effect by keeping Vds1 = Vds2 constant in the ratio • Iout = [(W/L) (1+λVds2 )/(W/L) (1+λVds1)]Iref. • Improves output resistance • Disadvantages • Less accurate. • Current becomes constant for quite large value of Vds e.g. in this case minimum Vds is 1.2 V. • Body effect is also present which disturbs the output current.
- 13. • A Wilson current mirror or Wilson current source is a circuit configuration designed to provide a constant current. • This circuit has the advantage of virtually eliminating the current mis-match of the conventional • current mirror thereby ensuring that the output current Iout is almost equal to the reference or input current IRef thus eliminating the drawbacks of cascode structure.
- 15. • Advantages: • Curve is much flatter than basic and cascode current mirrors. • Output resistance becomes even much higher than cascode current mirror. This is caused by two positive feedback effects. • Disadvantages: • Current becomes constant for quite large value of Vds e.g. in this case minimum Vds is 1.22V
- 16. Low voltage self cascode current mirror
- 17. • The small signal transfer analysis of this circuit at 20 μA gave the current gain, i.e. Iout/ Iin = 1, and output resistance as 10 MΩ. T he power d issipation f or t his i s high. • They can be used as load resistances in CM circuits. They can extensively be used where power supply requirements are not the constraint
- 18. • Advantages: • High performance since output current is constant for low value of Vds . • High output impedance. • Disadvantages: • Power dissipation is high.