Using Integrated Differential Preamps

[AdrianM]

Quite a few of the PI projects on these forums are using THAT1500 or INA217 integrated differential amplifiers implementing the classic instrumentation amplifier configuration in a single chip. The problem I see with these is that there is no access to the two feedback paths in the initial + and - stages. This means there's no opportunity to limit the excursions with back to back diodes (like Carl rightly keeps reminding everyone to do!). If I take these diodes out of my discrete implementation using 3xOP37, the response is significantly slower - by 5us~10us. Has anyone looked into this?

[Tinkerer]

Quite a few of the PI projects on these forums are using THAT1500 or INA217 integrated differential amplifiers implementing the classic instrumentation amplifier configuration in a single chip. The problem I see with these is that there is no access to the two feedback paths in the initial + and - stages. This means there's no opportunity to limit the excursions with back to back diodes (like Carl rightly keeps reminding everyone to do!). If I take these diodes out of my discrete implementation using 3xOP37, the response is significantly slower - by 5us~10us. Has anyone looked into this?

Op amps should not be driven into saturation. Yet, it is common practice in PI designs.
The penalty is an extended delay and deterioration of the signal quality.

The preamp is one of the places where significant improvements can be made.

Tinkerer

[hobbes_lives]

Here's a good article on using limiting diodes in the feedback circuit.

http://www.ecircuitcenter.com/Circui...p_limiter1.htm

[taliesin]

just acquired an lm733cn

might mess around with a diff pre amp , using lm733cn the datasheet says selectable gains of 10, 100, 400.it's a dual opamp.? i dunno i've got to use it in something.any ideas's ??