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

VDD VDD 2IQ ViC+vi io ViC+vi/2 ViC-vi/2 Io+ Io- IQ IQ IQ

VDD 2IQ Rs Rs ViC+vi/2 ViC-vi/2 Io+ Io- IQ IQ

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

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

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

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 = (Veff1 + 0.1~0.2)/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

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

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

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

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

A self-biasing version for mid to low Vdd: 2Vt + 6 Veff Vbn Vbb Rss

Chapter 7 Figure 09

Chapter 7 Figure 15