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

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

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

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

5. BJT Current Source (Sink)

6. Current Source Concepts
Gate Overdrive
Cascode Source
Von

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

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

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

10. Current Mirrors nFET Current Mirror pFET Current Mirror
GND
Iin Vb M5 Mb
Vout
Iout
Vdd Vb
Iin
Iout M7 M4
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 Iout = ( (W/L)5 / (W/L)b ) Iin Iout1 Iin Vout1 Vb GNDMb M5
GND
GND
Iout = ( (W/L)5 / (W/L)b ) Iin

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

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

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

16. 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
GND
GND
GND

17. 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
GND
GND
GND
Base current, n outputs,
identical b,
same emitter areas:
Iout = Iin / (1 + (1/ b) )

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