1. cc cc vbp vbp vbn VDD VDD VDD VDD VDD M16 M14 M3 M4 M13 Rbp vo+ CL vo-Rc cc Rc M1 vp vn
vbn M2 M7 M8
M11
M15
M12 M9
M10
Vcntrl
M17

2. Size 2, 3 to be the same, 1, 2 by current ratio, 6 and 1 the same.
Size R so that M2 has sufficient Vds.
Size 5 to be the same as 1, M4 has L4=(4~6)L5. Criterion for L4 is that M1 and M2 has sufficient Vds. M5
Vbn M5 M4
Vbn
Vbn M4 M3 M3 M6 M3 M1 M2 M1 M2 M1 M2
Vbb
Vbb

3. Current source can be generated by using a resistor Rdd.
Rdd = (Vdd-Vbn)/Ib, or Rdd = (Vdd-Vbn-Vgs5)/Ib.
VDD
VDD
VDD
Rdd
Rdd
Rdd
Vbn
Vbn
Vbn
Vbb
Vbb

4. Problem: how to set Vgg with respect to Vdd?
But that current is very sensitive to Vdd changes.
If Vgg is set with respect to Vdd, say Vdd – 1.5, then we can set Rdd = (Vdd-Vgg-Vsg)/Ib = (1.5-Vsg)/Ib.
With this Rdd and Vgg, Ib will not change when Vdd changes.
Rdd
Vgg
Problem: how to set Vgg with respect to Vdd?
Vbn M3 M1 M2

5. Solution: set Vgg to be one diode connection below Vdd.
Key: make M5 to have larger Veff than M4.
Sizing for desired Ib:
Size M1,2,3 to be the same, and M4 has about 3 time W, so that all of these 4 have about the same Veff.
Size Rb = (Veff ~0.2)/Ib.
Size M5 to have (1+a)Veff by using either a smaller W or longer L than M4.
Size Rdd around aVeff/Ib.
Sweep Rdd to achieve Ib.
VDD
Rdd
Vgg M4 M5
Vbn Rb M3 M1 M2

6. A simpler version, just to generate Ib.
VDD
A simpler version, just to generate Ib.
This is called the Widlar structure,
Or the Vdd insensitive Iref generator
Or the Vdd insensitive Ibias generator.
VDD M3 M4 M1 M2

7. This is the N-version of the same. Sizing strategy very similar.
VDD
VDD M3 M4
This is the N-version of the same.
Sizing strategy very similar.
Make M2,3,4 to have the same Veff.
Make M1 to have larger Veff.
Nominal value of Rss to be Veff difference divided by desired Ib.
Adjust Rss to achieve the desired Ib. M1 M2
Rss

8. Cascoded version for better Vdd insensitivity.M3 M4
Cascoded version for better Vdd insensitivity.
But requires high Vdd:
3Vt+5Veff, if Rss has about one Veff. M1 M2
Rss

9. Does not require high Vdd: M3 M4
Does not require high Vdd:
Vdd > Vt+5Veff, if Ib*R is about one Veff.
But Vds for M1 and M2 not the same
Vds for M3 and M4 not the same M1 M2
Rss

10. Does not require high Vdd: M4
Does not require high Vdd:
Vdd > Vt+6Veff, if Ib*R is about one Veff.
Vds for M1 = Vds for M2 Vds for M3 = Vds for M4
But: IR drop may not track Veff as temp changes M3 M1 M2
Rss

11. A version that supports low supply voltage: as low as Vt + 5Veff
VDD
VDD
VDD
VDD M4 M3 M1 M2
Rss

12. A self-biasing version for mid to low Vdd: 2Vt + 6~7 Veff
Vdd requirement higher
Power consumption 1/2
Vbn
Vbb
Rss

13. Chapter 7 Figure 09

14. Chapter 7 Figure 15