Amplifiers – Modulator-demodulator-type amplifier
Reexamination Certificate
2000-01-18
2001-09-11
Mottola, Steven J. (Department: 2817)
Amplifiers
Modulator-demodulator-type amplifier
C330S251000
Reexamination Certificate
active
06288605
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of power switching output stages, and more particularly, to amplifiers operating in Pulse Width Modulation (PWM). The invention is particularly useful for multichannel audio amplifiers that are configurable in different modes of operation by connecting their respective output power stages in parallel according to different schemes.
BACKGROUND OF THE INVENTION
In many applications, particularly in the field of power amplifiers for low and medium frequency signals, and primarily in the field of high efficiency audio amplifiers, a Pulse Width Modulation with switching frequencies of up to several hundreds of KHz is often a preferred approach. In these applications, the output power stage includes at least a power device switching the output to the supply line (HIGH SIDE DRIVER) and at least a complementary power device, switching the output to the ground line (Low SIDE DRIVER), driven by a digital PWM signal that may have a switching frequency of several hundreds of KHz.
PWM power stages are often realized monolithically on the same chip that contains the drive and control circuitry, and it is necessary to ensure that the turn-on of one or the other of the two power switching devices, respectively of one and the other switching branch of the output node, never happens before the other device has already started the turn-off. If so, this would increase the power dissipation in the superposition intervals and, because of the high switching frequency, could lead to the failure of the power devices.
To prevent such a destructive condition from occurring, a small time interval must be established, during which both power transistors of the output stage are turned-off. Such an interval is commonly referred to as “dead zone” or “dead time”. In all the applications where it is necessary to ensure a high accuracy (such as in low distortion audio applications), the dead time should be minimized for obvious reasons.
Commonly, to avoid a simultaneous turn-on of the two branches of a output power stage, a dead zone for prevention of accidental overlapping of the turn-on commands for the two complementary devices of the stage is determined, by suitable delay circuits, based on RC networks dimensioned to ensure a certain delay, that is established by considering the worst condition of operation. In practice it is very difficult or almost impossible to fully optimize the delay value introduced in the turn-on commands because of the impossibility of effective electrical values of the manufacturing process of the integrated circuit, of their temperature dependence as well as of the variability of the load and other parameters that may affect it in a more or less marked manner.
The known solutions do not allow an optimization for minimizing the dead time value to be introduced in the turn-on signal of the complementary pair of power transistors of the output stage. moreover, in many applications, as in high efficiency audio amplifiers, in order to ensure most efficient driving conditions, switching from a bridge to single ended driving modes and vice versa is often implemented.
SUMMARY OF THE INVENTION
The present invention offers an effective approach in the form of a particularly efficient and versatile power switching output stage in order to optimize the requirements set forth above.
The circuit of the invention provides a power stage which is exempt of the cross-conduction phenomenon (simultaneous conduction of the two power switching devices) and able to automatically adapt itself to any intervening variation of electrical parameters due to the spread of the manufacturing process of temperature and of the load. The circuit of the invention allows a plurality of output stages to be externally connected in parallel, according to a selected scheme in a simple and programmable manner, while ensuring a perfectly effective control of the switching conditions of the power devices from an off state to a conduction state, in any configuration.
Different paralleling schemes of the output stages of different amplification channels, according to a certain number of admitted configurations, are made possible or rendered easier by the present invention. For example, to obtain high output power from audio reproduction apparatuses installed in vehicles, loudspeakers of a relatively low resistance typically on the range of 1-0.5 Ohm can be used, while in other applications of lower output power and a larger number of channels, 4 Ohm loudspeakers can be used.
REFERENCES:
patent: 5963086 (1999-10-01), Hall
Botti Edoardo
Ranieri Danilo
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Galanthay Theodore E.
Mottola Steven J.
STMicroelectronics S.r.l.
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