Amplifiers – Combined with automatic amplifier disabling switch means
Reexamination Certificate
1999-11-24
2001-11-27
Shingleton, Michael B (Department: 2817)
Amplifiers
Combined with automatic amplifier disabling switch means
C330S133000, C330S134000, C330S297000, C330S310000
Reexamination Certificate
active
06323729
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to an amplifier arrangement. Similar amplifier arrangements are already known in the art, such as “
Average efficiency of class-G power amplifiers
”, written by F. H. Raab,
IEEE Transactions on Consumer Electronics,
Vol CB-32, Nr May 2, 1986. Therein, class-G power amplifiers are described, including a first amplifier stage powered by a first couple of power supplies, and a second amplifier stage biased by a second couple of power supplies, the absolute value of the voltages delivered by this second couple of power supplies exceeding those of the first couple of power supplies. The output terminals of both amplifiers are coupled together and constitute the output terminal of the class-G amplifier arrangement. Furthermore, as can be observed from
FIG. 1
of this prior art article, this class-G power amplifier includes a drive control, which includes an input terminal coupled to the input terminal of the amplifier arrangement, and which includes four output terminals, two of which are coupled to two input terminals of the first amplifier stage, another two of which are coupled to two input terminals of the second amplifier stage. The function of the prior art drive control is to make sure that input signals whose peak amplitudes are between the first and second supply voltages as delivered by the first couple of power supplies, are amplified exclusively by the first amplifier, as is stated in the introductory part of the prior art article, and that for signals of larger amplitude, the drive, which corresponds to the input signal, is switched from the first amplifier to the second one.
Furthermore, as is also further mentioned in this and other prior art documents concerned with class G amplifiers, the amplifiers included in such prior art amplifier arrangements, consist of amplifiers with an emitter follower or source follower transistor configuration. As is well known by a person skilled in the art, such emitter followers have a very low output impedance and a high current amplification, both items being excellent for high current driving of a load.
Yet emitter followers have a very low voltage gain. When such class-amplifiers are used as an output stage of for instance a line driver amplifier configuration, the complete voltage gain of this amplifier configuration is to be provided by the input or pre-amplifier, which precedes the class-G amplifier. Since this pre-amplifier, as a consequence, also has to provide the complete output signal swing, this pre-amplifier is to be supplied by the higher voltage power supplies. This of course increases the current consumption of this preamplifier, while at the same time reducing its linearity.
SUMMARY OF THE INVENTION
An object of the present invention therefore is to provide an amplifier arrangement of the above known kind, but, which when used as an output stage in a larger amplifier configuration, solves the above mentioned drawbacks concerned with the high power consumption and poor linearity behaviour of the pre-amplifier preceding such an amplifier arrangement.
This object is achieved by the fact that the amplifier arrangement of the present invention has voltage gain larger than one.
In this way, by the fact that the amplifier arrangement has a voltage gain larger than one, the preceding pre-amplifier can be powered by the lower voltage power supplies, thereby solving the above mentioned drawbacks of power consumption and linearity in this pre-amplifier.
Another characteristic feature of the present invention is that a first input terminal (DCDIN
1
) of the drive control device (DCD) is coupled to a first output terminal (DCDOUT
1
) of the drive control device (DCD), with the drive control device (DCD) further including a third input terminal (DCDIN
3
) coupled to the output terminal (OUT) of the amplifier arrangement (AA), and a regulating device (D), an input terminal of which is coupled to a third input terminal (DCDIN
3
) of the drive control device (DCD), an output terminal of which is coupled to a fifth output terminal (DCDOUT
5
) of the drive control device (DCD), which is further coupled to the first output terminal (OUT
1
) of the first amplifier (AB), the regulating device (D) thereby being adapted to cut off the first amplifier (AB), based on the value of the output signal at the output terminal (OUT) of the amplifier arrangement (AA).
Thereby, the transition of the operation of the first amplifier to the second one, is controlled by means of the regulating circuit included within the drive control. As a matter of fact, the cited prior art article did not show any details about an actual implementation of such a drive control. In other prior art documents where such class G amplifiers are also described, the second amplifier usually incorporates the first one, such as for instance described in the article “
Highest Efficiency and super quality audio amplifier using MOS power FETS in class G operation
”, written by T. Sampei, S. Ohashi, Y. Ohta and S. Inoue,
IEEE Trans. on Consumer Electronics, Vol.
CE-24, Nr. Aug. 3, 1978. Therein the drive control for switching over from the first amplifier at low supply voltages to the one at high supply voltages and which includes the first one, consists of diodes in the first and second power supply path, as is explicitly shown in
FIG. 9
of this prior art document, and includes as well diodes in the input path in order to prevent switchover distortion, as is shown in
FIG. 8
of this prior art document. These prior art drive control devices thus control the switchover or transition point based on the voltage at the input signal. However, the use of diodes in the supply voltage path as well as in the input voltage path reduces the signal amplitude, and consequently the dynamic range.
By the regulating device of the drive control of the present invention, switchover of the operation from the first to the second amplifier is based upon the output signal of the amplifier arrangement which controls the cut off of the first amplifier via the output terminal of this first amplifier. No diodes are used in the input signal or supply voltage path because of the direct coupling between the input terminal of the amplifier arrangement and the first amplifier.
Another characteristic feature of the present invention is the drive control device (DCD) further includes a first current link (CL+), an input terminal of which is coupled to the first input terminal (DCDIN
1
)of the drive control device (DCD), an output terminal of which is coupled to the third output terminal (DCDOUT
3
) of the drive control device (DCD), the first current link (CL+) being adapted to generate at its output terminal at first current output signal which is dependent on the signal appearing at its input terminal, and which is further proportional to the current delivered at the first output terminal (OUT
1
) of the first amplifier (AB) in case the first amplifier is active.
The second amplifier is thereby controlled via a current signal which is derived from the input signal by means of the first current link. This allows the second amplifier to be a current amplifier, thus delivering the current gain to the amplifier arrangement.
The fact that the current output signal from the first current link is also dependent on the output current of the first amplifier, allows to regulate the transition from the operation from the first amplifier to the second one.
Yet further characteristic features of the present invention are that the drive control device (DCD) may further include a first voltage controlled current source (IREF
1
) which is coupled between the third voltage supply terminal (V
2
+) of the amplifier arrangement (AA) and a first junction point (J
1
) which is coupled between the output terminal of the first current link (CL+) and the third output terminal (DCDOUT
3
) of the drive control device (DCD), the current delivered by the first voltage controlled current source (IREF
1
) being dependent on the voltage at the first junction poi
Servaes Jan
Sevenhans Joannes Mathilda Josephus
Alcatel
Shingleton Michael B
Sughrue Mion Zinn Macpeak & Seas, PLLC
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