Amplifiers – With semiconductor amplifying device – Including class d amplifier
Reexamination Certificate
2000-07-31
2002-05-21
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including class d amplifier
C330S010000
Reexamination Certificate
active
06392484
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an amplifier system in general, and in particular to an amplifier system that can be operated in a linear output mode or a pulsed modulation output mode.
BACKGROUND
An amplifier system that drives a motor in high-precision industrial equipment should be accurate while maintaining a high level of energy transfer efficiency. Often high-precision industrial equipment, such as a lithography machine, has two modes of operation; a scanning mode and a stepping mode. In scanning mode, a positioning system positions a workpiece, such as a silicon wafer, in a precise and smooth manner. The workpiece is located on a stage. Thus, the amplifier system that drives a motor to move the stage in scanning mode should produce an accurate and linear output signal to the motor. Linear type amplifiers are therefore desirable for use in a high-precision positioning system while in scanning mode.
However, when the positioning system in the machine is in stepping mode, the workpiece on the stage is quickly moved from one position to the next. In stepping mode the positioning system generates large forces to accelerate and decelerate the stage to its new position. Thus, power transfer efficiency is important during stepping mode, and precision is less important. An amplifier system that produces a pulsed energy output, such as pulse width modulation (PWM) or pulsed period modulation (PPM), is highly efficient and therefore desirable for use in a positioning system while in stepping mode.
FIG. 1
is a schematic diagram of a dual stage amplifier system
10
used to produce a linear type output signal at terminal OUT as well as a PWM type output signal in response to an input signal at terminal IN. Amplifier system
10
includes a conventional linear amplifier output stage
20
with a PNP transistor
22
and a NPN transistor
24
arranged in a push-pull emitter follower configuration. Transistors
22
and
24
require resistors
25
,
26
, and diodes
27
,
28
to eliminate crossover distortion.
Amplifier system
10
also has a PWM amplifier stage
30
including transistors
32
and
34
. Transistors
32
and
34
in PWM amplifier stage
30
are turned off and transistors
22
and
24
are driven in their linear regions when a linear type output at terminal OUT is desired. When a PWM output is desired, transistors
22
and
24
in linear amplifier stage
20
are driven into saturation and the transistors
32
and
34
in PWM amplifier stage
30
are actuated. Thus, dual stage amplifier system
10
can be controlled to produce either linear type output signals or PWM type output signals.
The dual stage amplifier system
10
is disadvantageous because it requires two sets of transistors conducting simulatneously, resulting in decreased efficiency and precision. When amplifier system
10
is in PWM mode, the PWM output signal must be driven through saturated transistors
22
and
24
, which generate heat. Thus, in PWM mode, transistors
22
and
24
generate heat. Moreover, transistors
22
and
24
require resistors
25
,
26
, and diodes
27
,
28
to eliminate crossover distortion and, thus, further decrease efficiency.
SUMMARY
The present invention is directed to a single stage amplifier system that produces an accurate linear output signal, i.e., the output signal is directly proportional to the input signal, during low power demands or when high performance is desired, and produces a pulse modulated output signal when power transfer efficiency is desired such as during high power demands. The amplifier system includes a control circuit that switches between a linear mode control circuit and a pulsed mode control circuit to control a single output stage. The single output stage includes two transistors in a push-pull arrangement that are driven in their saturation regions when a pulsed output signal is desired, and are driven within their linear region when a linear output signal is desired.
In one embodiment, the single stage amplifier system of the present invention is used in a half-bridge amplifier system to drive a load, such as a motor, while in another embodiment the signal stage amplifier system is used in an H-bridge amplifier system.
REFERENCES:
patent: 4446440 (1984-05-01), Bell
patent: 5204594 (1993-04-01), Carobolante
patent: 5309078 (1994-05-01), Cameron
patent: 5329245 (1994-07-01), Hammond et al.
patent: 5723963 (1998-03-01), Li et al.
patent: 5731670 (1998-03-01), Galbiati et al.
patent: 5847602 (1998-12-01), Su
patent: 5963086 (1999-10-01), Hall
patent: 6016075 (2000-01-01), Hamo
patent: 0 082 282 (1983-06-01), None
patent: 2 693 856 (1994-01-01), None
patent: 7-202590 (1995-08-01), None
Choe Henry
Nikon Corporation
Skjerven Morrill & MacPherson LLP
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