Product category:
Discrete Power Devices
News Release from: Allegro MicroSystems Europe | Subject: LEXAM
Edited by the Electronicstalk Editorial
Team on 23 June 2003
MOSFET temperature compensation is a
sound idea
A new class of MOSFETs with built-in temperature compensation for enhanced audio performance has been developed by Sanken Electric in conjunction with the Pioneer Corp.
A new class of mosfets with built-in temperature compensation for enhanced audio performance has been developed by Sanken Electric in conjunction with the Pioneer Corp Known as LEXAM (legend of excellent audio mosfet), the new range not only offers highly accurate and responsive temperature compensation through the use of an on-chip diode: the devices also feature built-in push/pull circuitry that eliminates the need to trim the idling current in audio amplifiers using external components
This article was originally published on Electronicstalk on 30 Aug 2000 at 8.00am (UK)
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Temperature compensation is needed in mosfets used for audio amplification because variations in temperature can alter the transistor's operating point, with a detrimental effect on sound quality.
Traditionally, temperature compensation has been provided in a separate package, but such an arrangement has difficulty in following rapid changes in temperature, resulting in a time delay in the compensating function.
The ideal system would involve the temperature sensor to be located on the chip itself.
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In the new mosfet, a diode which is created during the existing mosfet manufacturing process is used to provide on-chip temperature compensation to an accuracy of within +/-1%.
The device also eliminates the need for compensating for idling-current variations at the manufacturing stage.
The idling current varies because of changes in 'on' voltage in individual devices or imbalances between complementary pairs, and is normally adjusted by external trimming components for each audio amplifier during manufacture.
If the need for these adjustments is removed, time and cost savings can be realised; in addition, the variations caused by manual adjustments are eliminated.
This is achieved in the new mosfet design by using a push-pull circuit along with a thick-film resistor on the substrate.
The resistance value is calculated and trimmed to obtain the optimum value to minimise variations in idling current.
Since the trimming is carried out on each individual mosfet to compensate for the device's particular characteristics, the resistance values after trimming are different for each mosfet.
The resulting deviation in the idling current is within +/-20% (100 +/-20mA).
Other characteristics such as forward transconductance are optimised to achieve the best possible audio performance.
Pioneer Corp has confirmed that the resultant sound quality has been dramatically improved by the optimisation of these characteristics and the built-in temperature compensation function.
Sanken semiconductor products are available in Europe via Allegro MicroSystems Europe.
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