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More bang for your buck

Maximising output power and quality from amplifiers in budget constrained designs. By Julian Hayes.

Decades of development and high volume production have brought an array of mature amplifier technologies to satisfy different market segments. Class A designs are traditionally used for more demanding applications, whilst Class B or AB amps provide more cost effective and power efficient alternatives. Performance can be traded off against power efficiency and component cost, and cost against output power.

The arrival of Class D technology has changed the balance, as power efficiency – once constrained between 30% and 50% – is reaching 90%. For a given output power, this allows supplies, heat sinks and housing to be smaller, whilst a 'louder' amp can be purchased for a given price.

A number of circuit topologies have emerged, including integrated devices and multichip solutions, where the modulator is separate from the output stage. The latter has the advantage of easy scalability: the same design can be reused for amplifiers with different output powers, as only the output stage and power supply needs to change. Segmenting the system in this way also allows the output stage to be built in a robust, high voltage technology suited to power switching devices, while employing a generic cmos process for the modulator. Digital signal processing functions – such as equalisation, dynamic compression or digital volume control – can then be integrated more easily with the modulator.

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Graham Pitcher

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