1. Field of the Invention
The present invention relates to a circuit apparatus, and more particularly, to a circuit apparatus having an electrostatic discharge (ESD) protection function.
2. Description of the Prior Art
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It is therefore one of the objectives of the present invention to provide a circuit apparatus having an electrostatic discharge (ESD) protection function in order to solve the above problem.
According to an embodiment of the present invention, a circuit apparatus having an ESD protection function is disclosed. The circuit apparatus includes a first circuit module, a second circuit module, and a thick-oxide transistor. The first circuit module operates in a first power supply domain and includes at least a first transistor. The second circuit module operates in a second power supply domain different from the first power supply domain and includes at least a second transistor. The thick-oxide transistor has a control terminal for receiving a control signal, a first terminal coupled to the first circuit module, and a second terminal coupled to the second circuit module, and the thick-oxide transistor is utilized for selectively performing an ESD protection operation according to the control signal. At least one of the first transistor and the second transistor is a thin-oxide transistor. The thick-oxide transistor is turned off by the control signal when an ESD event occurs, and the thick-oxide transistor is turned on by the control signal when the circuit apparatus is in normal operation mode.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
Certain terms are used throughout the following description and the claims to refer to particular system components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “include”, “including”, “comprise”, and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” The terms “couple” and “coupled” are intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.
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The thick-oxide NMOS transistor 230 has a control terminal (i.e. gate terminal), a first terminal coupled to the first circuit module 210, and a second terminal coupled to the second circuit module 220. The control unit 240 is coupled to the gate terminal of the thick-oxide NMOS transistor 230, and is for sensing whether an ESD event occurs to generate a control signal VB to turn off or turn on the thick-oxide NMOS transistor 230. In other words, the thick-oxide NMOS transistor 230 is utilized for selectively performing an ESD protection operation according to the control signal VB.
In a first embodiment of the present invention, the control unit 240 can be a bias voltage generating circuit including a PMOS transistor 242, a capacitor C1, and a resistor R1, as shown in
In a second embodiment of the present invention, the control unit 240 can be a charge pump coupled to a power supply. When an ESD event is detected, the charge pump does no action. The control signal VB will be low, and thus the thick-oxide NMOS transistor 230 will be turned off to perform the ESD protection operation between the first circuit module 210 and the second circuit module 220. When the circuit apparatus 200 is enabled (no ESD event occurs), the control signal VB will be high due to the charge pump pulling up the power supplyvoltage, and thus the thick-oxide NMOS transistor 230 will be turned on to let the circuit apparatus 200 return to the normal state. In this embodiment, the voltage level provided by the power supply that the charge pump is coupled to is not limited since the charge pump can pull it up to the desired voltage level.
Please note that the above embodiments are only for illustrative purposes and are not meant to be limitations of the present invention. The most important feature of the technical content disclosed by the present invention is the insertion of a thick-oxide transistor in the interface between different power supply domains to selectively perform an ESD protection operation. The thick-oxide transistor should be turned off to block the path between two power supply domains under ESD test, and should be turned on under normal situation. Because the thick-oxide device is much stronger than thin-oxide device and can endure high voltage, it is suitable for ESD protection implementation. A person of average skill in the pertinent art should be able to easily understand that various modifications and alterations of the circuit apparatus should fall into the disclosed scope of the present invention provided that the ESD protection function with a thick-oxide transistor in the interface between different power supply domains is present.
Briefly summarized, the circuit apparatus having the ESD protection function disclosed by the present invention is clearly capable of avoiding the ESD problems associated with the prior art, as well as maintaining a low cost and small chip area.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.