EP1952615A1

EP1952615A1 - Activation device

Info

Publication number: EP1952615A1
Application number: EP06841271A
Authority: EP
Inventors: Jean-François Mainguet
Original assignee: Atmel Switzerland SARL
Current assignee: Atmel Switzerland SARL
Priority date: 2005-11-25
Filing date: 2006-11-22
Publication date: 2008-08-06
Also published as: FR2894049A1; TW200809655A; WO2007060178A1; KR20080102124A; FR2894049B1; CN101313562A; JP2009517107A

Abstract

An activation process detects a passage of ridges and valleys of a fingerprint and generates a corresponding electrical signal. The electrical signal is filtered to produce a filtered electrical signal, and an activation signal is generated when an average level of the filtered electrical signal exceeds a threshold.

Description

ACTIVATION DEVICE

This disclosure relates to the activation of electronic devices. Background

An electronic device can have different operating states, such as an active state and a deactivated state. An active state can, for example, include an operational state in which the electronic device is fully functional. Conversely, a deactivated state can, for example, include a state in which the electronic device is in a power conserving mode, such as a standby mode. The electronic device can, for example, be activated from a deactivated state by a predefined activation input, e.g., a pressing of an input key or a combination of input keys; actuating a switch; opening a cover on the electronic device, etc. Such activation devices, however, are susceptible to unwanted activations by inadvertent actuations of input keys and/or increase the dimensions of the electronic device. Summary

Disclosed herein is an activation device and an activation process based on a sensor, such as a fingerprint sensor. In an implementation, the activation device is configured to activate an electronic device into an active mode. The activation device can, for example, include a sensor, a filter, and a threshold detector. The sensor can produce an electrical signal responsive to ridges and valley of a fingerprint. The filter can receive the electrical signal and filter the electrical signal to produce a filtered electrical signal. The threshold detector can receive the filtered electrical signal and provide an activation signal if the filtered electrical signal exceeds a threshold. In an implementation, the filter includes a bandpass filter, and the activation signal is generated if the filtered electrical signal exceeds the threshold during a predetermined time period.

In an implementation, an activation process detects a passage of ridges and valleys of a fingerprint and generates a corresponding electrical signal. The electrical signal is filtered to produce a filtered electrical signal, and an activation signal is generated when an average level of the filtered electrical signal exceeds a threshold for a predetermined time period. Brief description of drawings:

Fig.1 depicts a portable electronic device equipped with a sensor. Fig.2 depicts a cross-section view of an example sensor.

Fig.3 is a block diagram of an example activation control circuit. Fig.4 is a block diagram of another example activation control circuit.

Detailed description of preferred embodiments:

Fig. 1 depicts a portable electronic device 10 equipped with a sensor 12. In an implementation, the portable electronic device 10 can be a mobile telephone, and the sensor 12 can be a fingerprint sensor. In Fig.1 , the mobile telephone 10 can, for example, have a standby function to minimize the consumption of energy. The device 10 can include hardware and/or software for switching automatically to standby mode after a predetermined period of idleness. The mobile phone 10 shown includes the fingerprint sensor 12 and associated circuits to ensure recognition of the user and authorize operation by the user. In one implementation, the fingerprint sensor 12 comprises a sweeping sensor that includes a narrow bar of several lines of multiple pixels that provide successive fingerprint image data as the fingerprint is scanned. A representation of the fingerprint can be reconstructed by combining the fingerprint image data provided. An example sensor 12 of this type is described in patent FR-A-2 749 955.

In an implementation, the fingerprint sensor 12 can be inactive when the electronic device 10 is in a standby mode. A portion of the sensor 12, however, can be maintained in an active state and facilitate an activation function. In one implementation, one or more pixels in the fingerprint sensor 12 can be maintained in an active state.

The fingerprint sensor 12 can, for example, be a pyroelecthc or piezoelectric (pyroelecthc or piezoelectric materials generally have both pyroelecthc and piezoelectric properties) sensitive film sensor, that is, a sensor in which pixels are sensitive to the temperature or pressure of the ridges of the fingerprint in direct or almost direct contact with the sensitive film, and likewise sensitive to the absence of the ridges, i.e., the fingerprint valleys.

The reactivation pixel or pixels i.e., the one or more pixels maintained in the active state, can be placed next to the bar of fingerprint detection pixels, or be part of the bar itself. In the second implementation processing is provided to read the signal coming from these reactivation pixels so that the whole bar need not be kept in an active state.

Fig. 2 depicts a cross-section view of an example sensor 12. A finger is being swiped across the sensor 12. The cross-section view of the sensor 12 depicts a bar of three pixel lines L1 , L2, L3, and an adjacent pixel Pr used for reactivation. The reactivation pixel Pr can, for example, be similar to the other pixels of the bar. In one implementation, the adjacent pixel Pr is an isolated pixel and measures approximately 50 micrometers on each side. Other pixel dimensions can also be used, however. The processing of the signal from pixel Pr is shown in figure 3, which is a block diagram of an example activation control circuit.

The reactivation pixel Pr supplies the signal representing the scrolling of the ridges and valleys of the fingerprint to an amplifier A which remains active when the electronic device 10 is in standby mode. The signal from amplifier A is transmitted to a filter FB. The filter FB can, for example, band pass filter the signal from pixel Pr to retain only a frequency spectrum included between the two frequencies F1 and F2. The frequencies included between F1 and F2 are chosen so that interval F1 -F2 contains most of the main variation frequencies of a signal representing the ridges and valleys of the fingerprint of a finger moving across the pixel at an expected rate. For example, an expected rate can be approximately 4 to 40 cm/s. These values are given as an example because they represent realistically the movement of the finger of a person asked to reactivate the apparatus by swiping his or her finger across the sensor. Other rates, however, can also be used. Selection of the frequencies F1 and F2 can be based on fingerprint dimensions and the selected rate. For example, if a typical fingerprint valley pitch is 450 micrometers, the frequencies F1 and F2 may have the following orders of magnitude: F1 from 100 to 200 Hz, and F2 from 1000 to 3000 Hz.

The bandwidth filter FB can, for example, comprise a single capacitor in series to eliminate the audio frequencies, including the continuous component of the signal, followed by a bandwidth filter. The capacitor will eliminate or reduce the frequencies below F1 , and the bandwidth filter can be configured to reduce or eliminate frequencies above F2 that is, the frequencies that are not highly representative of the deliberate swiping of a finger across the sensor.

The filtered signal is provided to a detector RD. In an implementation, the detection RD can, for example, comprise an average value detector RD. In an implementation, the average value detector RD generates an output signal that is based on a low frequency filtering and rectification of the signal output from the bandwidth filter FB. In this specification, reference made to an average value detector is in the broadest sense, be it an average value detector or a peak value detector. The average value detector, considered in this general sense, supplies a signal representing the overall average amplitude of the filtered signal variations. The output of the average value detector RD is applied to a threshold detector DTH. If the average value exceeds a determined threshold, the detector DTH supplies a signal to reactivate the whole of mobile device 10, or subsystems thereof. If the average value does not exceed this threshold, it will be considered that reactivation was not requested and the detector DTH will not supply a reactivation signal.

The absence of a detection signal may result from the fact that a finger was not swiped over the sensor 12, was unsuccessfully swiped, swiped too slowly, or swiped too quickly. In any case, the device 10 is not reactivated and awaits another swipe of the finger. Fig. 4 is a block diagram of another example activation control circuit. The circuit of Fig. 4 is similar to the circuit of Fig. 3, except that the threshold detector DTH is connected to a circuit DD capable of detecting a minimum duration of presence of the output signal from threshold detector DTH. Circuit DD can, for example, receive the detection signal from DTH then triggers the transmission of a pulse with a delay Tmin with respect to the detection signal (a monostable flip-flop can handle this function). By way of example, an AND logic gate can receive the detection signal and the delayed pulse. Thus a reactivation signal is generated only if the threshold detector signal is still present beyond the duration Tmin. If the output signal from threshold detector DTH stops before Tmin, no reactivation signal will be transmitted.

In another implementation, a user can be required to swipe the finger twice in opposite directions. The reactivation circuit can, for example, utilize a time-related sequence detector. For example, the reactivation circuit can include a structure with a time-related sequence template: the signal from the threshold detector must conform to this template to trigger the reactivation signal. Typically, the reactivation circuit can include hardware and/or software for executing an algorithm which does not result in the transmission of a reactivation signal unless the following conditions are met:

- no overrunning (exceeding) of the threshold for at least 0.5 second;

- then detection of overrunning for at least 0.1 second and at most 0.5 second; - then absence of overrunning for at least 0.1 second and at most

0.5 second;

- then detection of overrunning for at least 0.1 second and at most 0.5 second;

- finally, absence of any overrunning for at least 0.1 second. The example algorithm above detects a condition that is representative of the swiping of the user's finger in both directions. Other time periods may also be used.

Thus, in this example implementation, the reactivation circuit enables the transmission of an active mode switching signal if the threshold overrun detector supplies an overrun signal for a duration falling within an initial range of durations, followed by the absence of any overrun signal for a duration included in a second range of durations, lastly followed by another overrun signal for a duration included within a third range of durations. The three ranges can be identical as shown in the example given above; other ranges can also be used.

In another implementation, the sensor that is sensitive to the swiping of the fingerprint includes not only the first reactivation pixel Pr, but also includes a second reactivation pixel Pr'. The signals from these two pixels are applied to a finger swiping direction detection circuit DS. This circuit may be based on the correlation of the time related signals from each of the pixels. If a strong correlation is found between the time-related signal from Pr and the signal delayed by an interval of time dT, derived from Pr', this correlation indicates that pixel Pr' sees the finger before pixel Pr. Conversely, if strong correlation is found between the time-related signal from Pr' and the delayed signal from Pr', it means that pixel Pr sees the finger before pixel Pr'. The correlation can be sought with several successive delays dT, 2dT, etc. until a significant correlation is found. Correlation can include subtracting the two signals for a certain period of time and calculating the difference signal energy for that time. Having determined the direction of finger passage, matters can be arranged so that the reactivation signal is only transmitted if the average level of the detected and filtered signal exceeds a threshold for a minimum predetermined duration for each direction in which the finger is swiped.

Other implementations can be considered in which, for example, it is required to swipe the finger three times instead of two.

In an implementation, the filtering FB and detection DTH functions and algorithms are digitally implemented by the digitization of the signal outputted by amplifier A. A digital implementation can use less silicon surface than analog filters based on capacitors and resistors and also offers more practical adjustment of the templates because it can be arranged that they are programmed using memory registers, volatile or not.

Analog implementations can also be used, however. This written description sets forth the best mode of the invention and provides examples to describe the invention and to enable a person of ordinary skill in the art to make and use the invention. This written description does not limit the invention to the precise terms set forth. Thus, while the invention has been described in detail with reference to the examples set forth above, those of ordinary skill in the art may effect alterations, modifications and variations to the examples without departing from the scope of the invention.

Claims

1. A device for reactivating an electronic apparatus having an active mode and a standby mode, such device being designed to switch the apparatus from standby mode to active mode, comprising an elementary sensor capable of supplying an electric signal of a variable level corresponding to a swiping of ridges and valleys of a fingerprint in front of the sensor, a bandwidth filter receiving said electric signal and providing a filtered signal having reduced variations outside a determined frequency band, and an average signal level threshold detector to provide an active mode control signal for reactivating said apparatus only if said filtered signal has exceeded a predetermined threshold during a predetermined minimum period of time.

2. A reactivation device according to claim 1 , wherein said elementary sensor includes a sensitive zone smaller in size than the usual gap between the ridge and the valley of a fingerprint, typically measuring less than 100 micrometers.

3. A device according to claim 1 , wherein it includes means to enable a transmission of said active mode control signal if a duration of a threshold overrun by said filtered signal is included between two predetermined values.

4. A device according to claim 1 , wherein it includes means of enabling a transmission of said active mode control signal if the average signal threshold detector indicates overrun of the threshold for a duration falling within an initial range of durations, followed by the absence of any overrun for a duration included in a second range of durations, lastly followed by another overrun for a duration included within a third range of durations.

5. A device according to claim 1 , wherein said elementary sensor has at least one second sensitive zone (Pr') similar to said first mentioned sensitive zone, each sensitive zone supplying a respective signal and wherein the reactivation device includes means for: - determining from the two signals a direction of movement of the fingerprint,

- allowing transmission of said active mode control signal if at least two finger swipes, successively in different directions, are detected in a determined time interval and if the signal from at least one of the sensitive zones is above the threshold for a minimum duration for each swipe, within this time interval.

6. A device according to claim 1 , wherein the sensor is a piezoelectric or pyrotechnical film sensor or a capacitive detection sensor or an active detection sensor using a radiofrequency signal or an optical sensor using transmission or reflection.

7. A process for reactivating an electronic device having an active mode and a standby mode, comprising the following steps:

- detecting a passage of ridges and valleys of a fingerprint as it moves in front of a sensor that is sensitive to this movement, and generating a variable level signal corresponding to this movement,

- filtering in a bandwidth filter the variable level signal to reduce signal variations outside a determined frequency band characteristic of the swiping of a fingerprint in front of the sensor,

- and supplying an active mode control signal when an average level of the filtered signal exceeds a determined threshold for a minimum determined period of time.

8. A process according to claim 7, comprising detection of a passage of the finger in a first direction then a second direction, said active mode control signal being supplied only if the average level of the filtered signal exceeds the threshold for a minimum predetermined time for each direction of finger passage.

9. An electronic apparatus having an active mode and a standby mode, and having a fingerprint reader to provide security of use, said apparatus comprising a device according to claim 1 for reactivating said apparatus, wherein the elementary sensor of said device comprises at least one sensitive pixel formed in the fingerprint reader, said at least one pixel being maintained in active mode when the remainder of the reader is in standby mode.