Amplifiers – With semiconductor amplifying device – Including field effect transistor
Reexamination Certificate
1999-11-12
2001-09-25
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including field effect transistor
C330S296000
Reexamination Certificate
active
06294959
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to circuits that operate in a manner substantially complementary to amplifying devices they include, and to apparatuses, such as power amplifiers and stereo receivers, that incorporate such circuits. More particularly, the present invention relates to such a complementary-operating circuit that maintains its complementary operation over varying operating conditions.
BACKGROUND OF THE INVENTION
As is known, some circuit applications, such as audio amplifier applications, prefer or require active devices that are electrical complements of each other. For example, in audio amplifier applications that use vertical double-diffused metal oxide semiconductor field effect transistors (DMOS FETs), P-channel MOSFETs are coupled to their electrical complements, N-channel MOSFETs, to create a composite vertical DMOS device that provides a desired amplification of an audio input signal. However, as is also known, P-channel MOSFETs do not perform as well as N-channel MOSFETs and are more expensive to fabricate and purchase for comparable performance. The inferiority of P-channel MOSFETs is primarily due to inherent differences in N-type and P-type silicon. Consequently, a P-channel MOSFET that is a true electrical complement of an N-channel MOSFET cannot be made using current technology.
Instead of attempting to fabricate a P-channel MOSFET that is a true electrical complement of an N-channel MOSFET, semiconductor manufacturers attempt to match certain parameters of the P-channel and N-channel devices. However, matching of any two parameters of N-channel and P-channel devices causes other parameters of the devices to differ. For example, for the same voltage and current ratings, a P-channel MOSFET will have a higher on-state saturation resistance and a lower transconductance than a similar-sized N-channel MOSFET. To produce a P-channel device that has the same on-state saturation resistance and voltage rating as a particular N-channel device, the silicon die of the P-channel device must be larger than the silicon die of the corresponding N-channel device and, therefore, the P-channel device will cost more than the comparable N-channel device.
Some techniques for producing substantially complementary active devices are also known. For example, until the 1970's, PNP bipolar junction power transistors with performance similar to NPN bipolar junction power transistors were not available. To simulate the function of a PNP power transistor, an NPN power transistor
103
was used with a feedback circuit as depicted in FIG.
1
. The feedback circuit consists of a low power PNP transistor
101
and a resistor
105
. The combination of the NPN power transistor
103
and the feedback circuit provides an approximately “virtual” PNP transistor circuit
100
and is typically referred to as a “quasi-complementary” circuit. The common application of the virtual PNP transistor circuit
100
was in the output stage of a power amplifier.
Although the virtual PNP transistor circuit
100
provides some complementary operation, it has certain drawbacks. For example, it is difficult to select PNP and NPN transistors
101
,
103
for use in the virtual PNP transistor circuit
100
such that the respective direct current (DC) characteristics of the transistors
101
,
103
combine to provide a circuit with DC characteristics that are substantially complementary to the DC characteristics of the NPN power transistor
103
. Further, variation of the DC characteristics of the NPN power transistor
103
, particularly current gain, with varying operating conditions causes the dynamic characteristics of the virtual PNP transistor circuit
100
to deviate from the dynamic characteristics of a true complement of the NPN power transistor
103
.
Therefore, a need exists for a circuit that operates in a manner substantially complementary to an amplifying device included therein that can cost-effectively simulate a P-channel MOSFET for use in complementary MOSFET circuit applications and that can maintain complementary operation over varying operating conditions. An apparatus, such as an audio power amplifier or a stereo receiver, that incorporates such a circuit would also be an improvement over the prior art.
SUMMARY OF THE INVENTION
The present invention overcomes the foregoing problems and limitations of the prior art by providing, according to one aspect thereof, a circuit that includes a voltage controlled voltage source (VCVS) coupled to a three-terminal amplifying device, whereby when an input signal is applied to a negative input terminal of the VCVS, the circuit operates in a manner substantially complementary to the amplifying device. Prior art complementary-operating circuits that do not include a VCVS do not maintain their complementary operation over varying operating conditions. By contrast, the use of a VCVS in the circuit of the present invention enables the circuit to operate in a manner substantially complementary to the amplifying device over all specified operating conditions.
According to another aspect of the present invention, the VCVS includes a differential amplifier, a signal translation amplifier, and an amplifying device driver circuit, each of which preferably includes one or more bipolar junction transistors (BJTs) in sharp contrast to the single PNP BJT driver circuit employed in the prior art. The preferred arrangement of BJTs in the differential amplifier, the signal translation amplifier, and the amplifying device driver circuit enables the VCVS to maintain a desired voltage gain (preferably unity) over all specified operating conditions.
According to yet another aspect of the present invention, the aforesaid complementary-operating circuit forms part of a power amplifier and/or a stereo receiver to enhance the overall performance of such stereo components.
These and other aspects and advantages of the invention will become more apparent to a person of ordinary skill in the art upon review of the following detailed description of a preferred embodiment taken in conjunction with the appended drawings in which like reference numerals designate like items.
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General Electric Transistor Manual, Chapter 11, p. 263 No month and no year.
Choe Henry
Holland & Knight LLP
Pascal Robert
LandOfFree
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