week_14 - Modified version of wide-swing high-Z current...

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Modified version of wide-swing high-Z current mirror Advantages compared to previous circuit: Has smaller dissipated power 2 1 of the one + dissipation Of cascode stage. And smaller area, and also more stable! One device split in two transistors. . . . . . . . . . . . . n V 70 casc . 7 Q 70 6 Q in I . 70 . 2 Q 3 Q . in out I I = 1 Q bias I 4 . bias I 4 Q 10 10 70 5 Q 10 >> Folded cascode OPAMP Modern OPAMPs are designed to drive capacitive loads No need to have low output impedance No need for last stage buffers Can design higher speeds and larger signal swings.
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All nodes are low-impedance except output node that is connected to a load capacitor In the order of 1/transistor transconductance Low impedance also helps reducing the voltage swing. So all nodes are under low voltage swing except for the output. Compensation is done by using load capacitance: more more stable slower L C Instead of voltage gain, transconductance gain becomes important: OTA V i in out (Operational Transconductance Amplifier) Folded cascade is an example of high output impedance OTAs.
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Amplifier is actually just a single stage cascade Amp. out V 2 Q . 1 Q . 2 bias I . . . . + _ in V V V 1 B 2 B . 1 bias I 3 Q 4 Q 12 Q 13 Q 5 Q 7 Q 9 Q 6 Q 8 Q 10 Q . .. . L C . . . 11 Q Differential-input to single-ended output Diode-connected and off during normal operation Constant transconductance circuit Current mirrors are wide swing Æ high output impedance for current mirror results in large gain. Cascode stage consist of opposite transistor types. B V out in Wide-swing cascode current mirror B V out in For differential output stage we need to use 2 of these wide swing current mirror stages.
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1 Bias I is a constant transconductance biasing circuit and are connected to and respectively.
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week_14 - Modified version of wide-swing high-Z current...

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