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LM13700 OTA with Opamps instead of on-chip darlingtons
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KammutierSpule



Joined: Feb 07, 2008
Posts: 40
Location: Aveiro - Portugal

PostPosted: Sat Feb 01, 2020 3:46 pm    Post subject: LM13700 OTA with Opamps instead of on-chip darlingtons
Subject description: why?
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I have seen some designed using the LM13700 OTA that instead of using their on-chip darlington, they use an external Opamp to the effect.

What they are trying to solve by using Opamps?
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ixtern



Joined: Jun 25, 2018
Posts: 143
Location: Poland

PostPosted: Sat Feb 01, 2020 4:32 pm    Post subject: Re: LM13700 OTA with Opamps instead of on-chip darlingtons
Subject description: why?
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KammutierSpule wrote:
I have seen some designed using the LM13700 OTA that instead of using their on-chip darlington, they use an external Opamp to the effect.

What they are trying to solve by using Opamps?

There may be some answers:
- universal design: as LM13600 and LM13700 buffers are differs slightly, not using buffers allows to use either of them;
- tighter control of circuit parameters: op amps are more predictable then transistors and usually have better parameters;
- a habit: some designers feel better with op amps than transistors.
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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Sun Feb 02, 2020 8:08 am    Post subject: Re: LM13700 OTA with Opamps instead of on-chip darlingtons
Subject description: why?
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ixtern wrote:
a habit: some designers feel better with op amps than transistors.

Although I don't really design circuits with OTAs I do generally prefer opamps over transistors. Main reason being that opamps can sink AND source
while a transistor can only do one of those things. Also I seem to recall that using the internal darlington transistor of the OTA adds a DC offset which
you will have to compensate.

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