It's probably same thing as with MCP6024: two dual dice can be installed together to realize a quad. The top die gets its V+ in bottom left and V- in bottom right. The bottom die is rotated 180° so its supply connections are swapped.
When I designed my super low noise DC differential amplifier, I deliberately used the LTC1151 dual because separate chopper stabilized amplifiers would run at slightly different frequencies creating the potential for beat frequencies. Two separate dies are unlikely for this reason unless the clocks can be synchronized. Some of the older single chopper-stabilized parts have a clock pin which can be used for synchronization to avoid this problem.
They describe it as "chopper stabilized" in the datasheet. If you think about it, the part S1, gm1, gm2, S2 is a chopper amplifier: S1 chops the differential input voltage into a square wave, the linear transistors amplify the square wave, and S2 demodulates it back into DC by sampling the peaks. To avoid differential subtraction of peaks and valleys at this point, gm3 works as a DC servo of sorts and ensures that the valleys are fixed near some internal "ground" potential.
The output of the chopper feeds gm4 and gm5, which provide additional gain. And the whole chopper is bypassed at frequencies near the chopping frequency and above in order to reduce aliasing artifacts and achieve GBW much higher than the chopping frequency.
Of course the "auto zero" explanation about gm3 canceling gm1 offset voltage and a bunch of sample-and-hold circuits making it all work is valid too. I'm not sure what the difference between "chopper stabilized" and "auto zero" is supposed to be, and if there is any real difference at all. Maybe it's only marketing talk.
I have read some articles and it seems that (today) it is common sense that "Auto Zero" is used for sampling circuits which meassure the offset and subtract it from the amplified signal. "Chopper" is used for for circuits that modulate and demodulate the signal and so loose the offset on the way. But the naming is mixed up a lot... 
You are right, the sampling circuit is somehow a modulation too but in my view it´s a lot more a sampling thing.
"Stabilized" (chopper or auto-zero) means that there is a high frequency path parallel (at least that is what the articles said I have read).
I gave up trying to figure out the difference between auto-zero and chopper-stabilized. Descriptions from different manufacturers use different terms and contradict each other.
I think Linear Technology gave the best description for their chopper-stabilized parts. The zeroing amplifier measures and corrects its own offset, and then measures and corrects the offset of the main amplifier. One of the claimed features of their early parts is that they could be used in inverting or non-inverting mode, which I suspect was in response to true chopper amplifiers which could only be used in inverting mode.
Home
Help
Search
Login
Register
Recent Posts