Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Rectangular or pulse waveform width control
Reexamination Certificate
2000-03-16
2001-06-19
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Rectangular or pulse waveform width control
C327S175000, C332S110000
Reexamination Certificate
active
06249161
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electronic circuits, and more specifically to methods and devices for generating a pulse signal with modulable-width pulses.
2. Description of Related Art
Pulse width modulation (PWM) signals, which are pulse signals with modulable-width pulses, have many applications. For example, such signals are used to drive power transistors that control the current flowing through an electric motor, such as those used in the automobile industry for controlling electric windows, sunroofs, and windscreen wipers. Conventionally, a set-point signal (generally with a “sawtooth” form) is generated using an oscillator, and is compared with a control voltage by a comparator. The output of the comparator then delivers the pulse signal, whose duty cycle is determined by the value of the control voltage.
In certain applications, either a continuous analog voltage or a logical signal with two states (0 or 1) can be used as the control signal (for example, to produce a pulse control signal whose two levels are 0 and 5 volts). In other words, it may be necessary to carry out “analog” PWM control or “logical” PWM control in certain applications. Although conventional circuits for generating PWM pulse signals operate correctly when the control signal is a continuous analog voltage, such conventional circuits have operating problems when a logical signal is supplied to the input of the comparator as the control signal. In particular, problems are caused by instabilities in the PWM signal when the two inputs of the comparator are equal (for example, both at 0 volts).
SUMMARY OF THE INVENTION
In view of these drawbacks, it is an object of the present invention to overcome the above-mentioned drawbacks and to allow logical or analog PWM control using the same electronic circuit.
Another object of the present invention is to allow a PWM pulse signal whose duty cycle is independent of temperature to be generated.
One embodiment of the present invention provides a method for generating a pulse signal with modulable-width pulses. According to the method, a set-point signal is generated, and the set-point signal is compared with a control signal so as to produce the pulse signal. When the control signal is a two-state logical signal, a first reference voltage is taken as the set-point signal. When the control signal is a continuous analog voltage, the set-point signal is varied between the first reference voltage and a predetermined second reference voltage, which is higher than the first reference voltage. In a preferred method, the difference in level between the first reference voltage and the logical signal is greater than the offset voltage of a comparator that performs the comparison.
Another embodiment of the present invention provides a device for generating a pulse signal with modulable-width pulses. The device includes a set-point signal generator for generating a set-point signal, a control signal generator for generating a control signal, and a comparator that receives the set-point signal and the control signal. The comparator outputs the pulse signal. Further, the set-point signal generator includes a first voltage source for generating a first reference voltage, and a second voltage source for generating a second reference voltage, which is higher than the first reference voltage. In a first operating state, the generated set-point signal varies between the two reference voltages, and in a second operating state, the first reference voltage is supplied as the set-point signal. Additionally, the control signal generator can generate both a continuous analog voltage and a two-state logical signal. The set-point signal generator is operated in the first operating state when the control signal generator generates the continuous analog voltage as the control signal, and in the second operating state when the control signal generator generates the logical signal as the control signal. In one preferred embodiment, the device also includes a capacitor having a terminal that is coupled to ground, with the first voltage source being coupled between the first input of the comparator and another terminal of the capacitor; and short-circuit means for selectively grounding the first terminal of the capacitor.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only and various modifications may naturally be performed without deviating from the present invention.
REFERENCES:
patent: 5361048 (1994-11-01), Baum et al.
patent: 5455530 (1995-10-01), Huppenthal
patent: 6084451 (2000-07-01), Choi et al.
patent: 28 45 598 (1979-04-01), None
patent: 2845598A1 (1992-09-01), None
patent: 503571A1 (1992-09-01), None
patent: 0 503 571 (1992-09-01), None
Bongini Stephen C.
Fleit Kain Gibbons Gutman & Bongini P.L.
Galanthay Theodore E.
STMicroelectronics S.A.
Wells Kenneth B.
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