Electrical computers: arithmetic processing and calculating – Electrical analog calculating computer – Particular function performed
Reexamination Certificate
1999-02-10
2001-07-31
Mai, Tan V. (Department: 2121)
Electrical computers: arithmetic processing and calculating
Electrical analog calculating computer
Particular function performed
Reexamination Certificate
active
06269388
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a circuit for generating a trapezoidal signal with controlled wavefronts, particularly for a converter of a satellite receiver.
More particularly, the invention relates to a circuit for generating a trapezoidal signal which is used as a regulated amplitude-modulated supply voltage for a satellite receiver.
BACKGROUND OF THE INVENTION
It is known that a converter for a satellite receiver, commonly referred to as an “LNB,” is supplied by a device that also performs logic control of the LNB.
In particular, such a device, sometimes referred to as an “LNBP,” is a dual-output voltage supply having a regulated output voltage that can be amplitude-modulated by means of a trapezoidal signal generated in the device itself. The modulating signal is detected by the satellite receiver for band control.
The modulating signal should have characteristics, in terms of frequency, duty cycle, rise and fall times, which comply with standards used by many satellite receiver manufacturers.
A difficult problem to solve is controlling rise and fall times of the modulating signal, which have an upper limit and a lower limit. The lower limit is required because very fast wavefronts, generated by high-frequency harmonics, can compromise satellite signal reception quality.
The upper limit is instead necessary because very slow wavefronts are comparable with the period of the modulating signal and would, therefore, compromise recognition of the modulating signal by the satellite receiver.
The problem is currently addressed by using discrete components, such as by using a square-wave oscillator followed by a low-pass RC filter. This device powers and controls the satellite receiver by means of a coaxial cable. Control of a reception band of the satellite receiver is performed by means of a square-wave signal with controlled fronts.
FIG. 1
illustrates a square-wave oscillator
1
followed by a low-pass pass RC filter
2
. In this manner, a square-wave signal from the oscillator is filtered by the RC filter
2
, whose output signal is a trapezoidal waveform signal having an amplitude equal to an amplitude of the square-wave signal generated by the oscillator
1
.
The trapezoidal output signal is added to a reference voltage so that the output of the device is amplitude-modulated with a preset peak-to-peak amplitude of the modulating signal. The sum of the trapezoidal waveform signal and the reference voltage is provided by the OR gate
3
. The output of the OR gate
3
is sent to an operational amplifier
20
having a transistor
21
connected to an output thereto.
This technique has inaccuracies and has a drawback of having little correlation between the frequency of the modulating signal and the rise and fall times of the modulating signal. In particular, there is no link between the frequency of the square wave and the rise and fall times. In this manner, it is possible to have a high frequency and long-lasting fronts, thereby leading to problems in recognizing the signal.
Accordingly, this system requires dual trimming of the capacitances of the oscillator
1
and of the RC filter
2
. Furthermore, the above-described system provides low precision in the amplitude of the modulating signal, and further entails a need to normalize the amplitude of the modulating signal with respect to the reference voltage, such that the amplitude of the modulated output is preset.
SUMMARY OF THE INVENTION
An advantage of the present invention is to provide a circuit for generating a trapezoidal signal with controlled wavefronts, such as for a converter for a satellite receiver, which provides a correspondence between the oscillation frequency and the rise and fall times of the wavefronts without using external components.
Another advantage of the present invention is to provide a circuit for generating a trapezoidal signal with controlled wavefronts, such as for a converter for a satellite receiver, in which an output signal can be precisely amplitude-modulated.
Another advantage of the present invention is to provide a circuit for generating a trapezoidal signal with controlled wavefronts, such as for a converter for a satellite receiver, in which a square-wave signal can have precisely controlled rising and falling fronts.
Another advantage of the present invention is to provide a circuit for generating a trapezoidal signal with controlled wavefronts, such as for a converter for a satellite receiver, which can be highly reliable and relatively easy to manufacture at competitive costs.
Embodiments of the invention provide a circuit for generating a trapezoidal signal with controlled wavefronts, such as for a converter for a satellite receiver, the circuit comprising a first oscillator to generate a square-wave signal and a second oscillator cascade-connected to the first oscillator, wherein the second oscillator is synchronized with said first oscillator and is suitable to generate a voltage signal which is amplitude-modulated with a trapezoidal modulating signal.
REFERENCES:
patent: 4016496 (1977-04-01), Eastcott
patent: 4064406 (1977-12-01), Tiemeijer
patent: 4514820 (1985-04-01), Mirow et al.
patent: 4563548 (1986-01-01), Misherghi et al.
patent: 4672568 (1987-06-01), Taylor
Galanthay Theodore E.
Iannucci Robert
Mai Tan V.
Seed IP Law Group PLLC
STMicroelectronics S.r.l.
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