L12 lecture

L12 lecture - OTA Realizations Single stage OTA Single high...

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EECS 240 Lecture 12: Two Stage OTA B. Boser 1 OTA Realizations Single stage OTA Single high impedance (voltage gain) node Near maximum power efficiency Limited gain and/or output range Can be combined with cascodes, gain boosting •E x a m p l e s : Telescopic OTA Maximum power efficiency Limited input common-mode range Folded cascode Large input common-mode range Slightly improved output range Folding adds noise and power penalty Multi stage OTA Advantages over single stage OTA Reduced interaction between gain and output range Somewhat higher drive capability for given C in Disadvantages Increased power dissipation or reduced speed Need for compensation x a m p l e s : Miller-compensated 2-stage OTA OTA with preamp (power efficiency?) Nested Miller compensation EECS 240 Lecture 12: Two Stage OTA B. Boser 2 Multi-Stage OTAs Advantage – Higher gain – Improved output voltage swing – Potentially reduced input capacitance – Power dissipation? Noise? Challenges – Stability: needs compensation (usually) – Reduced bandwidth (2 … 3 times smaller per added stage) Approaches – 2 high-gain stages with Miller compensation – Wide-band preamp (e.g. T. Cho, JSSC 3/95) – Nested Miller compensation (e.g. G&M, 4 th ed.)
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EECS 240 Lecture 12: Two Stage OTA B. Boser 3 2-Stage OTA Example M1a M1b M4b M=2 M3b M6c M=2 M5c M=2 M2b M7b V xx M2a M7a V bias2 V bias1 M3a M4a M=2 V bias5 V
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L12 lecture - OTA Realizations Single stage OTA Single high...

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