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Hello Byliu,
Conceptually, this is the type of circuit you would look for using either bipolar power transistors, or power MOSFET devices:
Google search on a term such as "External Output Transistors Boost Output Current" or "Op amp output buffer circuit."
Here is an older TI/NSC Applications Report on the subject. The general information is still applicable:
http://www.ti.com/lit/an/snoa600b/snoa600b.pdf
I hope this helps get you started.
Regards, Thomas
Precision Amplifiers Applications Engineering
Hello Byliu,
The dead zone you are referring to is associated with the class AB biasing of the complementary NPN/PNP output stage. Class AB reduces the output stage operating current when the output isn't delivering output current. That biasing increases the efficiency of the stage and reduces power dissipation. Increasing the idle current reduces the crossover distortion, but increases the power dissipation.
Fortunately, the effect of crossover distortion is reduced by negative feedback. The naturally occurring crossover distortion is divided by, and reduced by, the available loop gain; the difference between the open-loop gain (Aol) and closed-loop gain (Acl). Therefore, operating the op amp/buffer output stage with the lowest closed-loop gain, maximizes the loop-gain and minimizes the crossover distortion. It probably isn't apparent to most op amp users but in most cases the internal output stage in their favorite op amps is biased class AB as well. That goes for TI's high-performance audio op amps that produce THD + N, Total harmonic distortion + noise numbers on the order of 0.00005% (OPA1652). Therefore, class AB biasing is a good compromise, between distortion and power dissipation.
Please understand that achieving the 18 to 20 bit performance you are attempting is going to be challenging. There are things that may arise that haven't considered at this point, but all you can do is move forward and knock them down one at a time. Using a very high performance op amp such as the OPA211 gets you off to a good start.
Regards, Thomas
Precision Amplifiers Applications Engineering