Amplifiers – Modulator-demodulator-type amplifier
Reexamination Certificate
1999-12-07
2001-11-06
Pascal, Robert (Department: 2817)
Amplifiers
Modulator-demodulator-type amplifier
C330S20700P, C330S251000
Reexamination Certificate
active
06313697
ABSTRACT:
The invention relates to a device for amplifying input signals, comprising a control stage and a switching bridge amplifier, which is coupled to said control stage via at least first and second control signals, the bridge amplifier being switchable in at least two states in dependence upon the control signals.
The invention also relates to an audio system and a hearing aid provided with such a device.
Such a device is disclosed in U.S. Pat. No. 5,387,875. In audio systems and hearing aids, such devices are often used to amplify audio signals. The device known from said United States patent document comprises an oscillator for generating a triangular reference signal, and first and second comparators for generating, respectively, a first and a second control signal. An input signal to be amplified is converted to the first control signal in the first comparator by comparing the input signal with the reference signal. Similarly, the input signal inverted by an inverter is converted to the second control signal in the second comparator by comparing the inverted input signal with the reference signal. Subsequently, the input signal is amplified by supplying the control signals to a switching bridge amplifier composed of four switches.
The switching bridge amplifier incorporated in the known device may be in four different states. These states are diagrammatically shown in
FIGS. 2A through 2D
. The
FIGS. 2A and 2B
show two active states of the bridge amplifier, wherein the bridge amplifier supplies power to a load
48
. The
FIGS. 2C and 2D
show two passive states of the bridge amplifier, wherein the bridge amplifier does not supply power to the load
48
. In the known device, all four states of the switching bridge amplifier are controlled by the control stage.
In the known device, relatively much power is dissipated in the bridge amplifier.
It is an object of the invention to provide a device of the type mentioned in the opening paragraph, in which relatively little power is dissipated in the bridge amplifier.
To achieve this, the device in accordance with the invention is characterized in that the control stage is embodied so as to control only a single substantially passive state of the bridge amplifier. In the known device, both passive states of the switching bridge amplifier, as shown in
FIGS. 2C and 2D
, are controlled by the control stage.
The invention is based on the recognition that the relatively high power dissipation in the known device is caused by the large number of switching operations performed by the switches in the bridge amplifier. The switching operation performed by a switch causes a small amount of power to be dissipated in the switch. These so-called switching losses are reduced in the device in accordance with the invention by controlling the bridge amplifier in such a manner that it can only be in one of the two passive states. The other passive state is not controlled. As a result, the switches in the bridge amplifier have to perform fewer switching operations, so that less power is dissipated.
An embodiment of the device in accordance with the invention is characterized in that the control stage comprises a conversion unit for converting the input signals into sign and magnitude-coded signals, said control stage also comprising a pulse width modulator for converting the magnitude of the coded signals to pulse width-modulated signals, and the control stage further comprising a generator for generating the control signals from the pulse width-modulated signals and the sign of the coded signals. It has been found that the control signals can be readily generated in this manner.
A further embodiment of the device in accordance with the invention is characterized in that the pulse width-modulated signals comprise at least bivalent signals, the generator being embodied so as to control the passive state of the bridge amplifier when the pulse width-modulated signals have a substantially low value. By virtue thereof, a simple implementation of the generator is achieved.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 3931581 (1976-01-01), Kush, Jr. et al.
patent: 5075634 (1991-12-01), French
patent: 5387875 (1995-02-01), Tateno
patent: 5442317 (1995-08-01), Stengel
patent: 5506493 (1996-04-01), Stengel
patent: 5617058 (1997-04-01), Adrian et al.
patent: 6097249 (2000-08-01), Strickland et al.
Dijkmans Eise C.
Neuteboom Harry
Nguyen Patricia T.
Pascal Robert
U.S. Philips Corporation
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