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# MOS Current Mirror - PowerPoint PPT Presentation

MOS Current Mirror. Section 9.2 J. Ou. A Simple Current Mirror. Example 1. Example #2. Trade-Offs in Current Mirror Design. Output resistance (1/gds) CDS W/L Current. I OUT =100 uA. For Same IOUT, L↓→W↓→GDS↑(Ro↓) →CDS ↓. Drop in Ro is not desired.

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## PowerPoint Slideshow about ' MOS Current Mirror' - guy-ingram

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### MOS Current Mirror

Section 9.2

J. Ou

• Output resistance (1/gds)

• CDS

• W/L

• Current

IOUT=100 uA

For Same IOUT,

L↓→W↓→GDS↑(Ro↓) →CDS ↓

Drop in Ro is not desired.

Use Cascode to Increase output Resistance

Rout is approximately gm3ro3ro2

L1=L2, but L3 need not equal to L2.

Design Criteria: Choose Vb so that VY and VX.

We will learn how to generate Vb in the next class.

VDS of T4 is not matched to VDS of T5.

T4 has VDS of 999.1 mV. How come?

Answer: VSD=0.2 was used as design criteria for T0 and T2.We need a transistor to absorb the difference between

VDS of T4 (which is 0.6 V) and VSD of T2 (which is 0.2V)

Bias I:

100 nA

VDS5=161.2 mV gives 50 nA

VDS4 is 155.7 mV, provides 49.82nA.

T1 is designed to have a VSD of 0.4, leading to Vout=0.6 V.

T3 is designed to have VDS of 200 mV, but it must sustain Vout=0.6 V.

So we need to add a transistor to absorb the difference in V.