SGS-THOMSON Presents Innovative Audio Amplifier and Smart Power IC for Photographic Camera at ISSCC

21 February 1996 -- SGS-THOMSON Microelectronics announced last week new developments in the field of power integrated circuits at the 1996 International Solid-State Circuits Conference (ISSCC) in San Francisco. A new type of audio power amplifier -- the class SB amplifier -- and a complex smart power chip designed with Polaroid Corp. for a new photographic camera.

In their paper 'A High Efficiency 4x20W Monolithic Audio Amplifier for Automobile Radios Using a Complementary DMOS BCD Technology', Edoardo Botti, Tiziana Mandrini and Fabrizio Stefani presented a new audio power amplifier design that reduces power dissipation by as much as 45%.

This integrated circuit embodies a new approach named class SB where the amplifier works in single-ended configuration up to a certain power level then switches to a bridge arrangement. This concept can now be applied in a practical circuit because mixed Bipolar-CMOS-DMOS (BCD) technology makes it possible to integrate a lossless DMOS switch.

High efficiency is very important in car radios because there is very little space in a standard size car radio case for heatsinks. By improving efficiency it is possible to obtain the high power that consumers demand without the need for a very large heatsink. One way to achieve this high efficiency is to use a class D switching amplifier. However this solution requires more components and causes radiation problems. The new SGS-THOMSON design solves the dissipation problem but at the same time it needs no more components than a normal class AB solution and generates minimal radiation.

The class SB high efficiency amplifier will be introduced commercially later in 1996.

The second paper, 'Single-Chip Smart Power Camera Controller with Photodiode Current Measurement Down to 3nA', is co-authored by Domenico Rossi, Giorgio Pedrazzini, Massimo Pozzoni, Giulio Ricotti and Enrico Ravenelli of SGS-THOMSON plus Elliott Strizhak and Mark Kackprowicz of Polaroid Corporation.

This paper describes a new custom power IC developed for a Polaroid photographic camera that integrates almost every circuit needed in the camera. This is a significant achievement because the circuit must accommodate on the same piece of silicon a high current motor driver plus a photodiode measuring circuit that handles currents as low as 3nA.

Programmed by the external microcontroller, which is the only function not integrated, the chip includes a 3A DMOS H bridge to drive the shutter motor, a strobe converter which drives an external flyback converter for the flash, a photodiode A-to-D converter, shutter motion feedback circuits and an on-chip low drop regulator which also powers the microcontroller. To prolong battery life the microcontroller can set a bit that switches off the regulator and brings system consumption down to under 500nA.

The new camera chip is assembled in a standard 44-lead Plastic Quad Flat Pack (PQFP44).

SGS-THOMSON is able to produce high-performance smart power chips thanks to a 1.2 micron advanced Bipolar-CMOS-DMOS technology that integrates very high density CMOS control circuits with very high efficiency DMOS power stages and high-precision bipolar analog functions. In this generation it is also possible to integrate a microcontroller on the chip.

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