Digital output MEMS pressure sensor and method

A method and pressure-sensor system provide a digital-frequency output linearly proportional to a sensed pressure. The system comprises a MEMS pressure-sensing element to provide a pressure-sensing output and voltage-to-frequency converter provide the digital-frequency output. The pressure-sensor system may also comprise an amplifier to provide an output voltage linearly proportional to the pressure. A temperature sensor and temperature-compensation circuitry provide a temperature-compensation signal to the amplifier to at least partially offset the effects of temperature on the system. Some embodiments of the present invention comprise a microcontroller system comprising a microcontroller and an RF transmitter. The microcontroller may receive the digital-frequency output and may generate a notification signal when the sensed pressure is inside or outside a predetermined pressure range. The RF transmitter may transmit an RF signal to indicate that the sensed pressure is inside or outside the predetermined pressure range.

TECHNICAL FIELD

Embodiments of the present invention pertain to electronic devices and systems, and in some embodiments, to pressure sensors and digital systems that sense pressure.

BACKGROUND

Conventional micro-electromechanical system (MEMS) based pressure sensors typically provide a non-amplified analog output voltage for measuring pressure. This low-level analog output voltage makes it difficult to integrate these conventional pressure sensors with digital systems, including microcontrollers and microprocessor based systems. To interface with such digital systems, additional circuitry must be designed and added. This increases cost and complexity. The low-level analog output voltage provided by such conventional sensors is also susceptible to noise and other interference reducing the accuracy of these conventional pressure sensors.

Some conventional pressure sensors include a digital interface, such as a RS-485 or RS-232 digital interface. These conventional pressure sensors are generally not suitable for many integrated circuit and on-die applications due to their large size and higher power consumption.

Thus there arc general needs for improved pressure-sensing systems and methods. There are also general needs for pressure-sensing systems and methods that provide a digital-frequency output, are less susceptible to noise, and/or may be connected directly to microcontrollers and microprocessor based systems. There are also general needs for pressure-sensing systems and methods that have reduced circuitry, are smaller in size, and require less power. There are also general needs for pressure-sensing systems and methods that eliminate the need for analog designers to design and fabricate interface circuitry helping to reduce cost, increase accuracy, and reduce complexity.

SUMMARY

In some embodiments, a method and pressure-sensor system provide a digital-frequency output linearly proportional to a sensed pressure. The system comprises a micro-electomechanical system (MEMS) pressure-sensing element to provide a pressure-sensing output and voltage-to-frequency converter to provide the digital-frequency output. The pressure-sensor system may also comprise an amplifier to amplify the pressure-sensing output and provide an output voltage linearly proportional to the pressure.

In some embodiments, an error-compensated pressure-sensor system and method are provided. In these embodiments, a temperature sensor and temperature-compensation circuitry provides a temperature-compensation signal to the amplifier to at least partially offset the effects of temperature on the system. In these embodiments, offset-and-gain compensation circuitry provide offset-and-gain compensation signals to the amplifier for error compensation.

Some embodiments of the present invention further comprise a microcontroller system comprising a microcontroller and/or an RF transmitter. The microcontroller may receive the digital-frequency output and may generate a notification signal when the sensed pressure is inside or outside a predetermined pressure range. The RF transmitter may transmit an RF signal to indicate that the sensed pressure is inside or outside the predetermined pressure range. In some embodiments, the RF transmitter may transmit an RF signal to indicate the actual sensed pressure at periodic intervals in time.

DETAILED DESCRIPTION

The following description and the drawings illustrate specific embodiments of the invention sufficiently to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. The scope of embodiments of the invention encompasses the full ambit of the claims and all available equivalents of those claims.

FIG. 1is a functional block diagram of a pressure-sensor system in accordance with embodiments of the present invention. Pressure-sensor system100comprises pressure-sensing element102to provide pressure-sensing output104proportional to a sensed pressure, and voltage-to-frequency converter110to provide digital-frequency output112. Digital-frequency output112may be linearly proportional to the sensed pressure. Pressure-sensor system100may also comprise amplifier106to amplify pressure-sensing output104and provide output voltage108linearly proportional to the sensed pressure. Voltage-to-frequency converter10may receive output voltage108and provide digital-frequency output112.

In some embodiments, pressure-sensor system100also comprises temperature sensor114and temperature-compensation circuitry116. Temperature-compensation circuitry116may be responsive to the output of temperature sensor114to provide temperature-compensation signal118at least to amplifier106. Temperature-compensation circuitry116may at least partially offset the temperature effects on the system and/or the various element of system100including amplifier106. Voltage-to-frequency converter110may provide a maximum frequency output when the pressure on pressure-sensing element102senses a maximum pressure. Voltage-to-frequency converter110may also provide a minimum frequency output when the pressure on the pressure-sensing element senses a minimum pressure. The minimum pressure may be substantially zero.

In some embodiments, pressure-sensor system100also comprises offset-and-gain compensation circuitry120to provide offset-and-gain compensation signals122to amplifier106. In response to offset-and-gain compensation signals122, amplifier106may provide substantially a zero-voltage output at a minimum or a predetermined pressure. In further response to offset-and-gain compensation signals122, amplifier106may provide a predetermined maximum output voltage at a maximum pressure or another predetermined pressure.

In some embodiments, clock-generating circuitry124, voltage-reference circuitry126and/or power-supply circuitry128are located off-die. In some embodiments, these elements may be part of a microcontroller system discussed in more detail below.

In some embodiments, pressure-sensing element102comprises a micro-electomechanical system (MEMS) pressure-sensing element. The MEMS pressure-sensing element may be fabricated within semiconductor die134. The sensed pressure may deform die134and pressure-sensing element102may provide either a capacitive or resistive output change in response to the sensed pressure, although the scope of the invention is not limited in this respect. This output may be amplified by amplifier106. In some embodiments, pressure-sensing element102may comprise a MEMS strain gauge, although the scope of the invention is not limited in this respect.

In some embodiments, pressure-sensor system100comprises on-die microcontroller130to provide digital-serial output132although the scope of the invention is not limited in this respect. Digital-serial output132may be generated from digital-frequency output112and a clock signal. Digital-serial output132may comprise a digital word indicating the sensed pressure. In some embodiments, microcontroller130may have a digital serial interface, such as a serial-peripheral interface (SPI), a microwave or RF interface, or an inter-integrated circuit (12C) interface to provide digital-serial output132, although the scope of the invention is not limited in this respect.

In some alternative embodiments, microcontroller130may be a microcontroller system and may include, among other things, one or more integrated multi-function timers and input capture and compare registers. In these embodiments, microcontroller130may capture and measure the frequency of signal112to determine the sensed pressure.

In some embodiments, pressure-sensor system100provides digital-frequency output112to a microcontroller system (not illustrated in FIG.1). The microcontroller system may determine the sensed pressure from digital-frequency output112and may generate a response signal for other system elements (not illustrated) when the sensed pressure is inside or outside a predetermined pressure range (e.g. too high, too low). Other system elements may be responsive to the response signal. In some embodiments, the microcontroller system and pressure-sensor system100are located on a single printed circuit board. In some embodiments, the microcontroller system may be fabricated on die136or may be located off die.

In some embodiments, pressure-sensor system100may detect an absolute pressure, although in other embodiments, two or more pressure-sensing elements102may be utilized to detect a pressure differential. In some embodiments, pressure-sensor system100may be used to detect pressure in washing machines, vacuum cleaners, HVAC systems, altimeters and tires. In some embodiments, pressure-sensor system100may be used in liquid-level detectors, blood-pressure meters, monitoring systems and gas-pressure detectors.

FIG. 2illustrates packaging200for a pressure-sensor system in accordance with embodiments of the present invention. Packaging200may be suitable for packaging pressure-sensor system100(FIG.1), although other packaging techniques may also be suitable. Packaging200may comprise package204and semiconductor die202mounted within package204. Semiconductor die202may include a pressure-sensing element, such as pressure-sensing element102(FIG. 1) and may correspond to die134(FIG.1). Packaging200may also comprise lid206having opening or hole208to allow a fluid, including a gas such as air or liquid such as water, to enter into cavity212of package204. Pressure from the fluid may deform die202and the pressure-sensing element may provide an output in response to the deformation of die202.

In some embodiments, packaging200further comprises coating210within cavity212. Coating210may at least partially cover die202. Coating210may be a silicone-gel coating, although other coatings are also suitable.

In embodiments, packaging200may further comprise an o-ring seal (not illustrated) around an opening or hole208to help prevent a liquid from escaping or leaking out In these embodiments, the pressure-sensor system may measure the pressure of the liquid.

In some embodiments, the pressure-sensing element102(FIG. 1) may be fabricated with first semiconductor die202, and amplifier106(FIG. 1) and the voltage-to-frequency converter110(FIG.1), among other elements, may be fabricated as part of second semiconductor die214. The first and second die may be coupled together and located within package204. In other embodiments, pressure-sensing element102(FIG.1), amplifier106(FIG. 1) and voltage-to-frequency converter10(FIG.1), among other elements, may be fabricated as part of a single semiconductor die located within package204.

In some embodiments, package204may be a lead-frame package comprising lead frames216to couple the package to a circuit board although the scope of the present invention is not limited in this respect. In these embodiments, lead frames216may couple to the die with bond wires218.

FIG. 3illustrates packaging300for a pressure-sensor system in accordance with other embodiments of the present invention. Packaging300may be suitable for packaging pressure-sensor system100(FIG.1), although other packaging techniques may also be suitable. In these embodiments, packaging300comprises die302, which may correspond with die202(FIG.2), lid306, which may correspond with lid206(FIG.2), opening or hole308, which may correspond with opening or hole208(FIG.2), coating310, which may correspond with coating210(FIG.2), cavity312, which may correspond with cavity212(FIG.2), and die314, which may correspond with die214(FIG.2). Packaging300may also include an o-ring seal (not illustrated) as discussed above.

Packaging300may be a surface-mount package comprising either a ceramic or laminate substrate305for attachment to a circuit board (not illustrated) with solder balls316. Wire bonds318may couple the die to solder-balls316. Packaging300may comprise dam304surrounding die302and die314and attached to substrate305. Coating310may be held in by dam304, at least before curing, and may at least cover the die302.

FIG. 4illustrates a pressure-monitoring system in accordance with embodiments of the present invention. Pressure-monitoring system400comprises pressure-sensing system402and microcontroller system404. Pressure-sensing system402and microcontroller system404may be mounted on circuit board406, although the scope of the invention is not limited in this respect. Pressure-sensor system100(FIG. 1) maybe suitable for use as pressure sensing system402, although other pressure-sensor systems may also be suitable. Pressure sensing system402may be packaged in packaging such as packaging200(FIG. 2) or packaging300(FIG.3), although other packaging is also suitable.

Pressure-sensing system402may comprise a pressure-sensing element, such as pressure-sensing element102(FIG.1), to provide a pressure-sensing output proportional to a sensed pressure. Pressure-sensing system402may also comprise a voltage-to-frequency converter, such as voltage-to-frequency converter110(FIG.1), to provide digital-frequency output412which may be linearly proportional to the sensed pressure.

Microcontroller system404may comprise a microcontroller and/or an RF transmitter. The microcontroller may receive the digital-frequency output, may determine the sensed pressure, and may generate a notification signal when the sensed pressure is inside or outside a predetermined pressure range. In some embodiments, the notification signal may be sent when a predetermined threshold is crossed and may represent that the pressure is low (e.g., outside a range), that the pressure is O.K. (e.g., inside a range)”, or that the pressure is high (e.g., outside a range). In some embodiments, the microcontroller may generate a notification signal at periodic intervals in time to indicate an actual sensed pressure.

The RF transmitter may transmit RF signal410with antenna408in response to the notification signal. In some embodiments, the RF transmitter may transmit an RF signal to indicate an actual sensed pressure at periodic intervals in time. In embodiments, RF signal410may indicate that the sensed pressure is inside or outside the predetermined pressure range. In other embodiments, microcontroller system404may transmit the notification signal over a wireline connection to other system elements. Antenna408may comprise a directional or omnidirectional antenna, including, for example, a dipole antenna, a monopole antenna, a loop antenna, a microstrip antenna or other type of antenna suitable for reception and/or transmission of RF signals which may be transmitted by microcontroller system404.

In some embodiments, microcontroller system404may include one or more integrated multi-function timers and input capture and compare registers. In these embodiments, microcontroller system404may capture and measure the frequency of signal412to determine the sensed pressure.

In some embodiments, microcontroller system404and pressure-sensor system402are located on single printed circuit board406. In other embodiments, microcontroller system404and pressure-sensor system402are fabricated as a single monolithic semiconductor device.

In some embodiments, pressure-monitoring system400may comprise a tire pressure-monitoring system. In this embodiments, pressure-sensing system402and microcontroller system404receive power from a small battery (not illustrated). In these embodiments, the tire pressure-monitoring system may be located within a tire, such as within the valve stem, although the scope of the invention is not limited in this respect. In other embodiments, pressure-monitoring system400may comprise product pressure-monitoring system for use in washing machines, vacuum cleaners, HVAC systems, and altimeters. In other embodiments, pressure-monitoring system400may comprise a liquid-level detector, a blood-pressure meter or a gas-pressure detector.

FIG. 5is a flow chart of a pressure-sensing procedure in accordance with embodiments of the present invention. Pressure-sensing procedure500may be performed by a pressure-sensor system, such as pressure-sensor system100(FIG.1), and/or a pressure-monitoring system such as pressure-monitoring system400(FIG.4), although other systems may also be suitable for performing procedure500. Although the individual operations of procedure500are illustrated and described as separate operations, one or more of the individual operations may be performed concurrently and nothing requires that the operations be performed in the order illustrated.

In embodiments, pressure-sensing procedure500may generate a digital-frequency output substantially proportional to a sensed pressure. Operation502provides a pressure-sensing output proportional to a sensed pressure. Operation502may be performed by a pressure-sensing element, such as pressure-sensing element102(FIG.1). In embodiments, the sensed pressure may deform a die comprising a pressure-sensing element. The pressure-sensing output may comprise a changing capacitive or resistive output, although the scope of the invention is not limited in this respect.

Operation504generates a temperature-compensation signal to at least in part offset temperature effects on the elements of the pressure-sensing system.

Operation506generates offset-and-gain compensation signals so that a substantially zero-voltage output at a minimum pressure may be provided. Operation506also generates offset-and-gain compensation signals so that a predetermined maximum output voltage may be provided at a maximum pressure.

Operation508amplifies the pressure-sensing output to provide an output voltage. The output voltage may be linearly proportional to the sensed pressure.

Operation510generates a digital-frequency output, which may be linearly proportional to the voltage provided in operation508. The digital-frequency output may further be linearly proportional to the sensed pressure.

In some embodiments, procedure500may include operations512through516. Operation512determines the sensed pressure based on the digital-frequency output and may also determine when the sensed pressure is inside or outside a predetermined pressure range. Operation514generates a notification signal when the sensed pressure is inside or outside the predetermined pressure range. Operation516wirelessly transmits the notification signal to another system element. Alternatively, operation516may transmit a notification signal over a wireline connection to other system elements.

In the foregoing detailed description, various features are occasionally grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the subject matter require more features that are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment.