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Current Sources

Current Sources. Ever wonder how we make one of these?. I out. Current Sink. V out. V b. M 5. GND. Current Sources. Ever wonder how we make one of these?. I out. Current Sink. V out. V b. M 5. GND. V dd. Current Source. V 1. M 6. I out. Current Sources. Ever wonder how

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Current Sources

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  1. Current Sources Ever wonder how we make one of these?

  2. Iout Current Sink Vout Vb M5 GND Current Sources Ever wonder how we make one of these?

  3. Iout Current Sink Vout Vb M5 GND Vdd Current Source V1 M6 Iout Current Sources Ever wonder how we make one of these?

  4. Iout Current Sink Vout Vb M5 GND Vdd Current Source V1 M6 Iout Current Sources Ever wonder how we make one of these? How “good” a current source? Early Effect

  5. BJT Current Source (Sink)

  6. Gate Overdrive Cascode Source Von Current Source Concepts

  7. Iout Iin Vout Vb Mb M5 GND GND Current Mirrors nFET Current Mirror

  8. Iout Iin Vout Vb Mb M5 GND GND Current Mirrors nFET Current Mirror Iout = ( (W/L)5 / (W/L)b) Iin

  9. Iout Iin Vdd Vdd Vout Vb Vb M4 M7 Mb M5 Iout GND GND Iin Current Mirrors nFET Current Mirror pFET Current Mirror Iout = ( (W/L)5 / (W/L)b) Iin

  10. Iout Iin Vdd Vdd Vout Vb Vb M4 M7 Mb M5 Iout GND GND Iin Current Mirrors nFET Current Mirror pFET Current Mirror Iout = ( (W/L)5 / (W/L)b) Iin Iout = ( (W/L)7 / (W/L)4) Iin A good way to generate a bias current

  11. Current Mirror Iout1 Iin Vout1 Vb Mb M5 GND GND Iout = ( (W/L)5 / (W/L)b) Iin

  12. Current Mirror Iout1 Iout2 Iout3 Iin Vout1 Vout2 Vout3 Vb Mb M5 M6 M7 GND GND GND GND Iout = ( (W/L)5 / (W/L)b) Iin

  13. Current Mirror Iout1 Iout2 Iout3 Iin Vout1 Vout2 Vout3 Vb Mb M5 M6 M7 GND GND GND GND Iout / Iin = ( (W/L)6 / (W/L)b) Iout = ( (W/L)5 / (W/L)b) Iin

  14. Current Mirror Iout1 Iout2 Iout3 Iin Vout1 Vout2 Vout3 Vb Mb M5 M6 M7 GND GND GND GND Iout / Iin = ( (W/L)7 / (W/L)b) Iout / Iin = ( (W/L)6 / (W/L)b) Iout = ( (W/L)5 / (W/L)b) Iin

  15. GND GND GND BJT Current Mirror No base current effects, same emitter areas: Iout = Iin Iin Iout Vi C

  16. GND GND GND BJT Current Mirror No base current effects, same emitter areas: Iout = Iin Iin Iout Base current, identical b, same emitter areas: Iout = Iin / (1 + (1/ b) ) Vi C

  17. GND GND GND BJT Current Mirror No base current effects, same emitter areas: Iout = Iin Iin Iout Base current, identical b, same emitter areas: Iout = Iin / (1 + (1/ b) ) Vi C Base current, n outputs, identical b, same emitter areas: Iout = Iin / (1 + (1/ b) )

  18. GND GND GND Diode-Capacitor Dynamics Iin Iout C (dVi/dt) = Iin - Iso exp(Vi/UT) Iout = Ico exp(Vi/UT) Vi C (C / Iout) (d Iout /dt) = Iin - Iout C (d Iout /dt) = Iout( Iin - Iout )

  19. Basic MOS Cascode Source(Sink)

  20. An Improved Source (Sink)

  21. One Further Improvement

  22. Adding Gain Increase Ro

  23. Low Saturation Voltage Source

  24. Current Source Design SPICE Results

  25. Current Sources • Basic concepts • Cascode Circuits • Advanced Cascode Circuits

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