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Difference between Op Amp and Transconductance Amp

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mengghee

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Can anybody tell me the difference between the op amp and transconductance amplifier ?
 

suhas_shiv

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Opamp is used to drive loads which are resistive or capacitive, whereas OTAs are used to drive purely capacitive loads(small cap loads). Also except for the input/output node all other nodes in an OTA are low impedance nodes unlike an opamp. Usually an OTA has 2 stages with no buffer, whereas an Opamp has a buffer stage. If you need more information regarding design, please refer to the Book CMOS circuit design by baker and Boyce.
 

    mengghee

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mengghee

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I am very new towards amp design.... what does purely resistive or capacitive load refer to ? can you give me a simple example of an implementation ? thank you very much
 

liuyonggen_1

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suhas_shiv said:
Opamp is used to drive loads which are resistive or capacitive, whereas OTAs are used to drive purely capacitive loads(small cap loads). Also except for the input/output node all other nodes in an OTA are low impedance nodes unlike an opamp. Usually an OTA has 2 stages with no buffer, whereas an Opamp has a buffer stage. If you need more information regarding design, please refer to the Book CMOS circuit design by baker and Boyce.

in my opinion, the load for OTA is not purely capacitive load because of the effect of itself output resistive load
 

    mengghee

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suhas_shiv

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When I say the load, I mean to say the stage after the OTA. If you consider a CMOS differential amplifier, its input is dominated by capacitance. Also, purely resistive and capacitive means that either the resistance or capacitance dominates( when I say purely, I don't mean to say literally, I guess the usage of the word purely was misleading, sorry for that). Refer the above book and maybe your doubts will be cleared.
 

mengghee

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I am getting more confuse. sorrie.... wondering if you can explain more... thank you
 

suhas_shiv

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Please go thru the book CMOS circuit design, simulation and layout by Baker and Boyce. It will give you some basic understanding about opamps and OTAs. If you still have doubts, I will try to help you out.
 

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surianova

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mengghee said:
I am very new towards amp design.... what does purely resistive or capacitive load refer to ? can you give me a simple example of an implementation ? thank you very much
or more simple way to understand is :

1. resistive load- when there is a path current sink to ground like driving resistor.
2. capacitive load- current have has no path sink to ground and only charge up
the capacitive load like driving capacitor.
 

    mengghee

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