CMOS comparator

Details CMOS comparator CMOS comparator

1998-05-07

2000-02-22

Tran, Toan

Miscellaneous active electrical nonlinear devices, circuits, and

Specific signal discriminating without subsequent control

By amplitude

327 81, H03K 522

Patent

active

060284579

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a CMOS comparator of the type preferably used in self-insulating power IC components.
So-called PROFETs (thermally protected field effect transistors) use such comparators to compare a measured voltage with a reference voltage. These conventional comparators require a relatively large amount of space, however, which obstructs the aim of high integration density.


SUMMARY OF THE INVENTION

The object of the present invention, therefore, is to provide a CMOS comparator with a low space requirement and which is able to output a wide voltage range for a small measurement signal, so that it can be used for switching inductive loads, for example.
In general terms the present invention is a CMOS comparator, particularly for power IC components, in which an input voltage is compared with a reference ground voltage. A voltage signal indicating a difference between the input voltage and the reference ground voltage can be tapped off at an output connection. A first current path is between a reference ground voltage connection and a bias voltage connection, and a second current path is between an input voltage connection and the bias voltage connection. Each of these has at least two first current mirrors and a second current mirror. A current source is arranged in the first current path between one of the first current mirrors and the second current mirror. The output connection is connected between one first current mirror and the second current mirror.
Advantageous developments of the present invention are as follows.
The first current mirrors have p-channel lateral high-voltage transistors which are connected in series with one another in the first and second current paths respectively. The drain of the first p-channel lateral high-voltage transistor is connected to a voltage which is more positive than a bias voltage present at the bias voltage connection.
The current source has an n-channel field effect transistor of the depletion type.
The second current mirror has n-channel lateral high-voltage transistors.
The present invention is also a current mirror switch having a CMOS comparator as described above wherein the high-voltage transistors in the first current mirrors serve as isolators between the CMOS comparator and the power output.
An output transistor is connected with its drain in the direction of positive voltage.
The CMOS comparator as claimed in the invention is distinguished by a simple design and hence a low space requirement. Four p-channel high-voltage transistors, which may preferably be lateral transistors, form two first current mirrors. In the current path on the reference or reference ground voltage side, a current source is then connected to the two p-channel high-voltage transistors in the two first current mirrors, this current source preferably being an n-channel field effect transistor. Another two n-channel high-voltage transistors are then connected to the current source and the two p-channel high-voltage transistors on the measured voltage side; these may also preferably be lateral transistors and form a second current mirror.
The bias current flowing in the current path on the reference side is determined by the current source. The high-voltage transistors in the two first current mirrors are "reversed", i.e. their high-voltage resistant drains are arranged in the direction of the more positive voltage, as compared with the voltages at the sources. This allows any negative voltage spikes to be controlled.
If the input voltage is equal to the reference voltage, then an identical current flows in both current paths since the high-voltage transistors in the cascaded two first current mirrors and in the second current mirror each have a very high dynamic output resistance.
The output voltage picked off between the high-voltage transistors in the first and second current mirrors reacts very quickly to discrepancies between the input voltage and the reference voltage. If the input voltage is smaller than the reference voltage, then th

REFERENCES:
patent: 4791324 (1988-12-01), Hodapp
patent: 5030903 (1991-07-01), Bernard et al.
patent: 5144223 (1992-09-01), Gillingham
patent: 5285168 (1994-02-01), Tomatsu et al.
patent: 5334929 (1994-08-01), Schade, Jr.
patent: 5353028 (1994-10-01), Wit et al.
patent: 5781043 (1998-07-01), Slemmer
patent: 5852376 (1998-12-01), Kraus
IEEE Proceedings of the 1988 Custom Integrated Circuits Conference, Oscar Agazzi et al, an Analog Front End for Full-Duplex Digital Tranceivers Working on Twisted Pairs, pp. 2641-2644.

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