Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Patent
1993-07-26
1996-04-02
Callahan, Timothy P.
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
327327, 327328, 327180, 327184, H03K 508, H03K 502, H03K 1200
Patent
active
055044468
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention applies to an ac voltage clipper to be used in MOS-circuits with an ac power supply. In that case the ac voltage has to be rectified by a rectifier. To protect the rectifier against damage caused by ac over-voltages at its input, it is necessary to limit the ac voltage by a clipper, if said voltage exceeds a predetermined threshold. The clipper should especially be applied in circuits where an ac voltage of highly varying amplitude is provided e.g. in the case of a LC-resonator influenced by an ac magnetic field.
SUMMARY OF THE INVENTION
The object of the invention is to provide an ac voltage clipper that has a short response time and a low current consumption when the clipper is not activated.
The ac voltage clipper according to the invention therefore is characterized in that the MOS-circuit has two input terminals which receive an ac supply voltage, which input terminals are each connected to one of two input terminals of the ac voltage clipper, the first input terminal of which is connected to a point of common voltage through a first MOS-transistor and the other input terminal is connected to said point of common voltage through a second MOS-transistor, the gates of the first and second MOS-transistors being connected to each other and receiving a gate voltage of a control circuit which gate voltage depends on the absolute value of the ac supply voltage, in such a way that when this absolute value exceeds a predetermined threshold value the first and second MOS-transistor are forced to be conductive.
In addition to a very short response time (ns range) and an extremely low current consumption (nA range) when the clipper is not activated, the ac voltage clipper according to the invention offers the advantage of a first order behaviour, a high current sinking capability (above 100 mA) and a small chip area. This is an unique combination of features for an ac voltage clipper in CMOS-technology
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further explained with reference to the drawings, in which
FIG. 1 shows an ac voltage clipper according to the invention.
FIG. 2a shows the ac voltage clipper of FIG. 1 in CMOS-technology.
FIGS. 2b and 2c show alternative elements for one element of the arrangement according to FIG. 2a.
FIG. 3 shows the connection of a rectifier to a clipper according to the invention.
FIG. 4 shows a clipper to be connected to the output of the rectifier according to FIG. 3.
FIG. 3 shows a rectifier converting an ac voltage, provided between the input terminals In1 and In2, into a dc voltage VDDUNS.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Since the rectifier itself is not part of the present invention, a detailed description thereof will be omitted.
To protect the rectifier against too high ac voltages at its input terminals, basically the output voltage of the rectifier can be simply limited with a single MOS-transistor, as is demonstrated in FIG. 4. However, MOS-bridge-rectifiers, as the one shown in FIG. 3, often have a rather large internal resistance, so that this kind of clipper still may result in high voltage differences and is therefore not efficient.
The best way of voltage clipping is to limit the ac voltage directly at the input of the rectifier. For this reason the circuit of FIG. 1 has been designed. In the clipper circuit according to the invention input In1' (which is connected to In1) is connected to the point of common voltage VSS through a NMOS-transistor MCL41, while input In2' (which is connected to In2) is connected to the point of common voltage VSS through a NMOS-transistor MCL42 (see FIG. 3). The gates of transistors MCL41 and MCL42 are connected to each other and through a depletion MOS-transistor MCL3, which is in "diode" configuration, they are connected to the voltage VSS. MOS-transistor MCL3 has a lower threshold voltage than the MOS-transistors MCL41 and MCL42. Input In1' is connected to the gate of transistors MCL41 and MCL42 through a diode DCL11 and a PMOS-transistor MCL2, while input In2' i
REFERENCES:
patent: 3571660 (1971-03-01), Phillips
patent: 3593112 (1971-07-01), Coats
patent: 4663547 (1987-05-01), Baliga et al.
patent: 4811191 (1989-03-01), Miller
patent: 4819147 (1989-04-01), Bingham
Callahan Timothy P.
Phan Trong
Sierra Semiconductor B.V.
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