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Interesting LT/Analog op amp

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  Interesting LT/Analog op amp bitrex <user@example.net> - 2018-10-02 12:22 -0400
    Re: Interesting LT/Analog op amp <698839253X6D445TD@nospam.org> - 2018-10-02 17:37 +0000
      Re: Interesting LT/Analog op amp Jeroen Belleman <jeroen@nospam.please> - 2018-10-02 21:39 +0200

#518133 — Interesting LT/Analog op amp

The LT1364/1365 dual/quad, 70MHz GBW and 1000V/uS slew rate:

<http://www.analog.com/media/en/technical-documentation/data-sheets/13645fa.pdf>

The simplified internal schematic is quite different than most 
traditional three-gain-stage V -> I -> V amps, looks like a cascade of 
"diamond"-configuration differential current amplifiers.

It's naturally not cheap about 6 bux in quantity for the quad, 12 in 
singles, but 1000V/uS and "stable into any capacitive load" wowie. 
anyone used them for anything here? The LTSpice test rig for the part is 
a 2MHz cutoff 4 pole Butterworth active filter from +5/-5 supplies.

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#518139

bitrex wrote
>The LT1364/1365 dual/quad, 70MHz GBW and 1000V/uS slew rate:
>
><http://www.analog.com/media/en/technical-documentation/data-sheets/13645fa.pdf>
>
>The simplified internal schematic is quite different than most 
>traditional three-gain-stage V -> I -> V amps, looks like a cascade of 
>"diamond"-configuration differential current amplifiers.

Dunno what you mean by 'diamond shape'
input is complementary emitter followers, nothing differential there, via R1 to next stage.

The opposite phases are generated by driving the complementary transistor emitters with R1.
Some current sources follow..
IN+ drives in fact .. complementary emitter followers... sets the working point.
Output is complementary emitter followers,

Temp tracking should be really good, else it distorts like ..

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#518146

On 02/10/18 19:37, 698839253X6D445TD@nospam.org wrote:
> bitrex wrote
>> The LT1364/1365 dual/quad, 70MHz GBW and 1000V/uS slew rate:
>>
>> <http://www.analog.com/media/en/technical-documentation/data-sheets/13645fa.pdf>
>>
>> The simplified internal schematic is quite different than most
>> traditional three-gain-stage V -> I -> V amps, looks like a cascade of
>> "diamond"-configuration differential current amplifiers.
>
> Dunno what you mean by 'diamond shape'
> input is complementary emitter followers, nothing differential there, via R1 to next stage.
>
> The opposite phases are generated by driving the complementary transistor emitters with R1.
> Some current sources follow..
> IN+ drives in fact .. complementary emitter followers... sets the working point.
> Output is complementary emitter followers,
>
> Temp tracking should be really good, else it distorts like ..
>

The term comes from the OPA660 'diamond transistor' which, I believe,
was the first to use this architecture in an IC. The complementary
emitter followers combined with the current mirrors behave much like
a single transistor, with a high impedance 'base' at +IN, a high 
impedance 'collector' at the C-Rc node and a low impedance 'emitter'
at the right side of R1, with the added twist that currents can be
flowing either way. It's a nice architecture really, although the
OPA660 never got very popular.

The LT1364 adds another emitter follower at -IN, turning it into
something resembling a long-tailed pair, but owing to the symmetry,
the 'tail' of the pair is no longer needed. A pity R1 is so high,
because that sets the transconductance of the central stage to a
very modest 2mS at most.

Jeroen Belleman

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