ho17.l14_current_bias

ho17.l14_current_bias - 1 Lecture 14 Supply Insensitive...

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Unformatted text preview: 1 Lecture 14 Supply Insensitive Bias Current Generation R. Dutton, B. Murmann Stanford University R. Dutton, B. Murmann 1 EE114 (HO #17) Poor Man's Bias R V V V I I OV t DD IN OUT = R. Dutton, B. Murmann 2 EE114 (HO #17) Issue: Current is essentially proportional to V DD E.g. if V DD varies by X%, bias current will roughly vary by the same amount 2 "V t " Referenced Bias ox IN t L W C I 2 V V V V + + By using a sufficiently large device, we can make V OV < V t, and achieve 2 2 OV t 2 1 GS OUT R L R V V R V I + = 2 t OUT R V I R. Dutton, B. Murmann 3 EE114 (HO #17) 2 Question: By how much will I OUT change given some variation in V DD ? Sensitivity The sensitivity of a parameter y to a change in parameter x can be approximately found using ! y x y / y y / y y x S x y y x x / x y / y x / x y / y = = In our case, we are looking for I I I I S S S IN OUT OUT IN I I I V I V OUT IN IN DD OUT DD 1 = R. Dutton, B. Murmann 4 EE114 (HO #17) % . V . V . V . . g . e V V V OV t OV 5 11 15 5 15 2 1 2 1 1 1 = + + Not bad, but also not all that great 3 Self Biasing In the circuit discussed on the previous slides, the supply sensitivity is still fairly high, because I IN is essentially directly...
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ho17.l14_current_bias - 1 Lecture 14 Supply Insensitive...

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