Abstract:
Active sensor circuitry for operating at low power and a low duty cycle while monitoring for an occurrence of an anticipated event.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to active sensor circuits, and in particular, to active sensor circuits required to operate at low power and low duty cycle. 
   2. Description of the Related Art 
   With recent advancements in semiconductor manufacturing and sensor technologies, low power sensor networks, particularly those operating wirelessly, are providing new capabilities for monitoring various environments and controlling various processes associated with or within such environments. Applications, both civil and military, include transportation, manufacturing, biomedical, environmental management, and safety and security systems. 
   Particularly for wireless sensor networks, low power operation is critical to allow for maximum flexibility and minimum form factor. It has been found that typical wireless sensor assemblies use upwards of 90% of their power merely on environmental or channel monitoring while waiting for the anticipated event(s) to occur. In other words, simply monitoring for the occurrence of an anticipated event requires the expenditure of nearly all available power. This is particularly true for acoustic sensors, which often require significant amounts of power. 
   This problem has been addressed thus far by having a low power, or “sleep,” mode of operation in which the back end of the sensor assembly, e.g., the signal transmitter, or “radio,” circuitry, is effectively shut down pending receipt of a signal indicating the occurrence of the anticipated event (e.g., a change in the local environmental conditions, such as acoustic noise or temperature). This can reduce power consumption of the sensor assembly to levels in the range of 10 to 50 percent of normal, or full power, operation. However, for a low duty cycle system where each sensor assembly may only spend a very small amount of time (e.g., 1%) performing data transmission, the power being consumed during such an idle period can still constitute a major portion of the overall power budget. 
   SUMMARY OF THE INVENTION 
   In accordance with the presently claimed invention, active sensor circuitry is provided for operating at low power and a low duty cycle while monitoring for an occurrence of an anticipated event. 
   In accordance with one embodiment of the presently claimed invention, active sensor circuitry for operating at low power and a low duty cycle while monitoring for an occurrence of an anticipated event includes early event detection circuitry and control circuitry. The early event detection circuitry is responsive to external environmental stimuli by providing a corresponding detected signal indicative of whether at least a portion of the stimuli is related to an anticipated event, and includes: a transducer responsive to the stimuli by providing a corresponding transducer signal; and detection circuitry coupled to the transducer and responsive to the transducer signal by providing the detected signal. The control circuitry is coupled to the early event detection circuitry and responsive to the detected signal by providing one or more control signals to control operation of downstream circuitry for further processing of the initial processed signal. 
   In accordance with another embodiment of the presently claimed invention, active sensor circuitry for operating at low power and a low duty cycle while monitoring for an occurrence of an anticipated event includes early event detector means and controller means. The early event detector means is for receiving external environmental stimuli and in response thereto providing a corresponding detected signal indicative of whether at least a portion of the stimuli is related to an anticipated event, and includes: transducer means for receiving the stimuli and in response thereto providing a corresponding transducer signal; and detector means for receiving the transducer signal and in response thereto providing the detected signal. The controller means is for receiving the detected signal and in response thereto providing one or more control signals to control operation of downstream circuitry for further processing of the initial processed signal. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a system functional block diagram of active sensor circuitry for operating at low power and low duty cycle while monitoring for an occurrence of an anticipated event in accordance with one embodiment of the presently claimed invention. 
       FIG. 2  is a functional block diagram of the signal classification and control circuitry of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   The following detailed description is of example embodiments of the presently claimed invention with references to the accompanying drawings. Such description is intended to be illustrative and not limiting with respect to the scope of the present invention. Such embodiments are described in sufficient detail to enable one of ordinary skill in the art to practice the subject invention, and it will be understood that other embodiments may be practiced with some variations without departing from the spirit or scope of the subject invention. 
   Throughout the present disclosure, absent a clear indication to the contrary from the context, it will be understood that individual circuit elements as described may be singular or plural in number. For example, the terms “circuit” and “circuitry” may include either a single component or a plurality of components, which are either active and/or passive and are connected or otherwise coupled together (e.g., as one or more integrated circuit chips) to provide the described function. Additionally, the term “signal” may refer to one or more currents, one or more voltages, or a data signal. Within the drawings, like or related elements will have like or related alpha, numeric or alphanumeric designators. Further, while the present invention has been discussed in the context of implementations using discrete electronic circuitry (preferably in the form of one or more integrated circuit chips), the functions of any part of such circuitry may alternatively be implemented using one or more appropriately programmed processors, depending upon the signal frequencies or data rates to be processed. 
   Referring to the figure, active sensor circuitry in accordance with one embodiment of the presently claimed invention includes early event detection circuitry with a transducer  102  and detection circuitry  104 , detection signal processing circuitry  130 , and signal transmission circuitry with media access control (MAC) circuitry  140  and interface circuitry  150  (e.g., providing the physical layer and wireless signal transmission interfaces). Additionally, in the case of a wireless sensor system, an antenna  152  is included. 
   During most of its operational life, the system  100  operates such that the early event detection circuitry  102 ,  104  is provided with and consumes a predetermined minimal power, while the downstream processing and interface circuits  130 ,  140 ,  150 , are effectively shut down with approximately zero power consumption. As the early event detection circuitry  102 ,  104  monitors the external stimuli via the transducer  102 , internal signal classification and control circuitry  104   c  monitors the intermediate signal  105   a . Upon reception of external stimuli  101  indicative of an occurrence of the anticipated event, the intermediate signal  105   a  is indicative of such event, and the control circuitry  104   c  provides control signals  105   c ,  105   d ,  105   e  to the downstream processing circuitry  130 , amplifier  104   a  and ADC  104   b . The amplifier control signal  105   d  controls the gain of the amplifier  104   a  as necessary to ensure adequate strength of the intermediate signal  105   a . The ADC control signal  105   e  controls the ADC  104   b  as necessary to ensure proper conversion of the analog intermediate signal  105   a  to the digital detected signal  105   b . The downstream control signal  105   c  initiates a turn-on, or “wake-up”, sequence of events within the downstream circuits  130 ,  140 ,  150  for processing and possible transmission of one or more data signals related to the detected signal  105   b . The downstream processing circuitry  130  performs the primary signal detection and processing operations, typically using a microprocessor, digital signal processor (DSP), or one or more dedicated application specific integrated circuits (ASICs). This helps ensure accurate detection of events, thereby minimizing signal throughput in the form of unnecessary signal transmissions when occurrences of events have been erroneously detected. 
   In accordance with one embodiment, the signal classification and control circuitry  104   c  monitors and classifies the low power intermediate signal  105   a  (e.g., corresponding to acoustic or vibration energy) and computes the signal energy to adjust the gain of the amplifier  104   a  to decide if the signal  105   a  indicates the occurrence of an anticipated event. For example, a simple classification can be made based upon an energy threshold. Alternatively, more complex analog classifications can also be made. If the occurrence of an anticipated event is indicated, the classifier would provide the appropriate control signals  105   c ,  105   e  to enable downstream processing to perform more processing for making a more accurate decision. 
   During most of its operational life, the system  100  operates such that the early event detection circuitry  102 ,  104  is provided with and consumes a predetermined minimal power, while the downstream processing and interface circuits  130 ,  140 ,  150 , are effectively shut down with approximately zero power consumption. As the early event detection circuitry  102 ,  104  monitors the external stimuli via the transducer  102 , internal signal classification and control circuitry  104   c  monitors the intermediate signal  105   a . Upon reception of external stimuli  101  indicative of an occurrence of the anticipated event, the intermediate signal  105   a  is indicative of such event, and the control circuitry  104   c  provides control signals  105   c ,  105   d ,  105   e  to the downstream processing circuitry  130 , amplifier  104   a  and ADC  104   b . The amplifier control signal  105   d  controls the gain of the amplifier  104   a  as necessary to ensure adequate strength of the intermediate signal  105   a . The ADC control signal  105   e  controls the ADC  104   b  as necessary to ensure proper conversion of the analog intermediate signal  105   a  to the digital detected signal  105   b . The downstream control signal  105   c  initiates a turn-on, or “wake-up”, sequence of events within the downstream circuits  130 ,  140 ,  150  for processing and possible transmission of one or more data signals related to the detected signal  105   b . The downstream processing circuitry  130  performs the primary signal detection and processing operations, typically using a microprocessor, digital signal processor (DSP), or one or more dedicated application specific integrated circuits (ASICs). This helps ensure accurate detection of events, thereby minimizing signal throughput in the form of unnecessary signal transmissions when occurrences of events have been erroneously detected. 
   Referring to  FIG. 2 , in accordance with another embodiment, the signal classification and control circuitry  104   ca  can provide more accurate detection than that of simple energy detection with energy detection circuits  110 ,  114   a ,  114   b , filters  112   a ,  112   b , and signal classifier circuitry  116 . The energy of the intermediate signal  105   a  is detected by an energy detection circuit  110  which provides the amplifier control signal  105   d  and a detected signal  111  which is provided to the signal classifier circuitry  116 . The energy of the intermediate signal  105   a  is also filtered by high pass  112   a  and low pass  112   b  filters. The respective energies of the filtered signals  113   a ,  113   b  are detected by energy detection circuits  114   a ,  114   b , which provide the resultant signals  115   a ,  115   b  to the signal classifier circuitry  116 . The signal classifier circuitry  116  processes (e.g., compares the relative magnitudes) these signals  111 ,  115   a ,  115   b  to determine whether an anticipated event has occurred. In the event that it is determined, by the signal classifier circuitry  116 , that an anticipated event has occurred, the additional control signals  105   c ,  105   e  are asserted as discussed above. 
   For example, for mechanical vibrations, the low frequency band energy is significantly larger than the high frequency band energy. If the anticipated event is a vibration, the system can turn on more accurately than simple average energy detection. The filters  112   a ,  112   b  can be easily implemented in low power analog circuits, which typically minimizes the system power needed. Further, the two bands (high pass and low pass) can be expanded to multiple bands or more specific band pass filters to achieve better performance for signals related to different anticipated events. 
   Referring to  FIG. 3 , in accordance with another embodiment, the signal classification and control circuitry  104   c  can provide more accurate detection than that of simple energy detection with energy detection circuits  110 ,  114   a ,  114   b , filters  112   a ,  112   b , and signal classifier circuitry  116 . The energy of the intermediate signal  105   a  is detected by an energy detection circuit  110  which provides the amplifier control signal  105   d  and a detected signal  111  which is provided to the signal classifier circuitry  116 . The energy of the intermediate signal  105   a  is also filtered by high pass  112   a  and low pass  112   b  filters. The respective energies of the filtered signals  113   a ,  113   b  are detected by energy detection circuits  114   a ,  114   b , which provide the resultant signals  115   a ,  115   b  to the signal classifier circuitry  116 . The signal classifier circuitry  116  processes (e.g., compares the relative magnitudes) these signals  111 ,  115   a ,  115   b  to determine whether an anticipated event has occurred. In the event that it is determined, by the signal classifier circuitry  116 , that an anticipated event has occurred, the additional control signals  105   c ,  105   e  are asserted as discussed above. 
   For example, for mechanical vibrations, the low frequency band energy is significantly larger than the high frequency band energy. If the anticipated event is a vibration, the system can turn on more accurately than simple average energy detection. The filters  112   a ,  112   b  can be easy implemented in low power analog circuits, which typically minimizes the system power needed. Further, the two bands (high pass and low pass) can be expanded to multiple bands or more specific band pass filters to achieve better performance for signals related to different anticipated events. 
   Various other modifications and alternations in the structure and method of operation of this invention will be apparent to those skilled in the art without departing from the scope and the spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. It is intended that the following claims define the scope of the present invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.