A New CMOS Voltage Divider Based Current Mirror, Compared with the Basic and Cascode Current Mirrors
- 1. A New CMOS Voltage Divider Based Current Mirror, Compared with the Basic and Cascode Current Mirrors By B.Nagajyothi
- 2. INTRODUCTION Current Mirrors made by using active devices have come to be widely used in analog integrated circuits both as biasing elements and as load devices for amplifier stages. The current mirror uses the principle that if the gate-source potentials of two identical MOS transistors are equal, then the current flown through their Drain terminals should be the same. The use of current mirrors in biasing can result in superior insensitivity of circuit performance to variations in power supply and temperature .
- 3. The use of current mirrors in biasing can result in superior insensitivity of circuit performance to variations in power supply and temperature . NMOS current mirrors are used as current sinks and PMOS current mirrors are used as current sources. There is variety of Current Mirror circuits available, each of them having their own advantages.
- 5. The transistor M11 is diode connected, forcing its Drain to Gate voltage to zero . In this mode transistor M11 operates in the saturation region, which in turns acts as a constant current source or reference current source. To work as a current mirror, both M11 and M12 are chosen to be identical MOS transistors. Neglecting the channel length modulation effect, if the gate-source of M12 is being biased to a fixed voltage produces a copy of reference current Iref at the Drain terminals of M12 transistor, denoted as Iout.
- 7. To achieve high output resistance, cascode current mirrors are used The transistor M11 and M15 are configured as diode connected, forcing to operates them in saturation region, which in turns acts as a constant current source or reference current source.
- 8. One of the advantages of Cascode Current Mirror is its ability to suppress the channel length modulation effects. This is been achieved by making Drain to Source Voltage of M11 and M12 are made equal, so Iout always tracks Iref. To work as a current mirror, both M11 and M12 are chosen to be identical MOS transistors.
- 9. IMPROVED VOLTAGE DIVIDER BASED CURRENT MIRROR
- 10. Improved circuit uses NMOS and PMOS transistors to form a Voltage Divider, so called as CMOS Voltage Divider based current mirror. NMOS and PMOS transistors are diode connected produces the reference voltage Vgs to bias the NMOS transistor M12, which in turns controls the Output Current Iout.
- 11. Output waveforms for basic current mirrors
- 12. Output waveforms for cascode current mirrors
- 13. Voltage divider based current mirror