REVIEW OF SCIENTIFIC INSTRUMENTS 80, 104701 2009 permalink
(the paper is presently a free download, which is cool)
I came across this as part of my "day job", but I suspect the author does audio design on the side, much like I do. It's an amplifier design for driving a piezo stack typically used in micropositioning applications. It has to output significant power into high capacitance loads at high frequencies. The author's solution was to bolt on a large current buffer onto the output of a simple op amp, what struck me as interesting was the relative elegance of the circuit, and the absence of feedback on the output stage. Feedback, it is claimed, actually reduces the circuit bandwidth... the analysis is a bit beyond me, I admit.
It is claimed that the circuit has high linearity, but would it make a good audio amplifier or not? The idea of a current buffer for an output stage is something I've played around with a bit in the form of MOSFET source followers, and liked very much... the circuit above would be the ultimate extension of that train of thought.
(a couple of ideas: use a power op amp like the LM3875 as the input, for a "power gainclone", or make a low power miniature version with a regular op amp for a pre-amp or headphone amplifier...)
(the paper is presently a free download, which is cool)
I came across this as part of my "day job", but I suspect the author does audio design on the side, much like I do. It's an amplifier design for driving a piezo stack typically used in micropositioning applications. It has to output significant power into high capacitance loads at high frequencies. The author's solution was to bolt on a large current buffer onto the output of a simple op amp, what struck me as interesting was the relative elegance of the circuit, and the absence of feedback on the output stage. Feedback, it is claimed, actually reduces the circuit bandwidth... the analysis is a bit beyond me, I admit.
An externally hosted image should be here but it was not working when we last tested it.
It is claimed that the circuit has high linearity, but would it make a good audio amplifier or not? The idea of a current buffer for an output stage is something I've played around with a bit in the form of MOSFET source followers, and liked very much... the circuit above would be the ultimate extension of that train of thought.
(a couple of ideas: use a power op amp like the LM3875 as the input, for a "power gainclone", or make a low power miniature version with a regular op amp for a pre-amp or headphone amplifier...)
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Hi Guys, I realize this thread is old, but I was surprised to see one of my circuit designs posted in an Audio forum.
The aim of this simple design was to provide a high bandwidth output stage with very low output impedance at high frequencies and large current. This combination is required to drive capacitive loads at MHz frequencies. Since the transistors are heavily forward biased and do not provide gain, the bandwidth is well above 10 MHz even though the output can deliver current in the Amps range.
The linearity would be on the order of 0.1% or worse so it's not a great candidate for an audio circuit, however by applying global feedback as described above, the linearity would become that of the driving opamp. There are a bunch of standard opamps with vanishingly small linearity that would suit.
Andrew
The aim of this simple design was to provide a high bandwidth output stage with very low output impedance at high frequencies and large current. This combination is required to drive capacitive loads at MHz frequencies. Since the transistors are heavily forward biased and do not provide gain, the bandwidth is well above 10 MHz even though the output can deliver current in the Amps range.
The linearity would be on the order of 0.1% or worse so it's not a great candidate for an audio circuit, however by applying global feedback as described above, the linearity would become that of the driving opamp. There are a bunch of standard opamps with vanishingly small linearity that would suit.
Andrew
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