ULP (ultra low power) amplifier

A self-indulgent inclusion especially for the curious. A seemingly complex design intended for mobile use that will, however, run on supplies that others could not, eg: solar.

To obtain maximum output voltage swing, bootstrapping is applied uniquely in two ways. The current source for the negative driver is taken to the output capacitor, instead of to ground. Similar use has been made of the positive half of the signal to boost the +ve supply voltage. To prevent over-driving the driver output is clamped by two diodes.

With a gain of 22 (low roll-off 150Hz, upper 868kHz), crossover distortion is reduced with the use of current sources and negative feedback. Useful and very compact versions of these were executed by the author using CA3046 transistor arrays on stripboard.

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