Semiconductor fingerprint extracting device
Technical field
The present invention relates to a kind of semiconductor fingerprint extracting device, it can gather the ridge of user's finger print and the pattern of paddy, and this semiconductor fingerprint extracting device can be used as a pixel cell of fingerprint image sensor integrated circuit.
Background technology
Fingerprint be human body inherent, with other people unique distinctively mutually invariant features.Fingerprint identification technology also is the technology that early is used as personal verification.As automatic fingerprint collecting, input technology, what extensively be known at present comprises: optical imagery, heat sensitive sensor, capacitance type sensor, human body far-infrared sensor etc.
Fingerprint is made up of ridge on a series of skin surfaces and paddy.The details that the uniqueness of fingerprint pattern is made up of these ridges and paddy determines.The representational details of being made up of these ridges and paddy generally includes: the arch of the bifurcated of ridge, the end of ridge, arch, tent formula, left-handed, dextrorotation, spiral and bispin etc.
When on user's the surface of finger presses at fingerprint sensor, the induced electricity pole plate of ridge on the skin surface and paddy range sensor far and near different, this has determined that the signal that is coupled on the battery lead plate by finger is strong and weak different, and the variation that goes out the signal power when sensor has also just detected the pattern of finger print.
Patent U.S.Pat.No.6636053 at U. S. application compares with the present invention, both technical fields and applications similar, but the very big difference of technical existence.Such as, used a charge integrator among the United States Patent (USP) U.S.Pat.No.6636053, the gain of charge integrator is that ridge or paddy are relevant with fingerprint on the sensitive surface; This structure is a single-ended structure.And the amplifier stage among the present invention is full both-end structure, is operated under two kinds of patterns, and its gain does not change with the situation of user fingerprints.As everyone knows, the single-ended mode circuit is vulnerable to the influence of the offset voltage of common mode interference and input stage; Single-ended export structure also easily makes signal be subjected to external interference in transmission course.
Summary of the invention
In order to overcome the shortcoming that single-ended structure had in the above-mentioned technology, the purpose of this invention is to provide a kind of semiconductor fingerprint extracting device, input, output terminal all are operated in difference modes in the structure of this device.
The present invention includes layer protective layer, a drive electrode, an induction of signal level, an amplified signal level at least; The input of amplified signal level, output terminal are differential configurations, and the induction of signal level links to each other with amplified signal level and is positioned at the below of protective seam, and drive electrode and detected finger skin and induction of signal inter-stage constitute signal path.
More particularly; the present invention comprises layer protective layer; a drive electrode that drives by the signal excitation source, an induction of signal level that comprises at least one battery lead plate, one comprises a difference input, the amplifier of difference output and the amplified signal level of a pair of reset switch.Induction of signal level, amplified signal level are positioned at the below of protective seam as solid-state circuit, drive electrode and detected finger skin and induction of signal inter-stage formation signal path.
Described induction of signal level comprises the stray capacitance at least one battery lead plate and this battery lead plate.Described battery lead plate is positioned at the below of fingerprint extracting device protective seam.Described induction of signal level links to each other with amplified signal level.Described amplified signal level comprises amplifier and a pair of reset switch that difference input, a difference are exported; The input end of amplified signal level links to each other with amplifier input terminal, and the output terminal of amplified signal level links to each other with the output terminal of amplifier; Between the normal phase input end of described amplified signal level and the reversed-phase output, link to each other with reset switch respectively between inverting input and the positive output end.The output terminal of described amplified signal level links to each other with output circuit.
Hereinafter used some symbols, person of skill in the art will appreciate that, available expression symbol has various ways, and using these symbols is in order to simplify and the present invention rather than limitation of the present invention clearly to be described.
With Fig. 2 is example, when user's finger 50 by the surface 11 that is pressed in this semiconductor fingerprint extracting device 60 on the time, the skin and the battery lead plate 30 of finger 50 have constituted capacitor C
SThe two poles of the earth.Capacitor C
SSize be electric capacity two die openings from function.Capacitor C
SThe distance of two interpolars depends on the ridge of finger 50 skins on the surface 11 of this sensor, the variation of paddy: when being ridge on by the surface 11 that is pressed in this sensor, and capacitor C
STwo die openings from minimum, the capacitance maximum; When being paddy on by the surface 11 that is pressed in this device 60, capacitor C
STwo die openings from maximum, the capacitance minimum.
Because need bear regular the pushing of finger, the surface of this fingerprint sensor array element circuit must have high rigidity, wear-resistant, corrosion resistant protective seam 10.
It has been generally acknowledged that the skin surface of finger is equipotential.Among the present invention, signal source V
SBy drive electrode 20a signal is conducted finger 50 to the user, pass through capacitor C again
SConduct to difference input, difference output amplifier I
1An input end INP.Signal is exaggerated device I
1Amplify back output.For unattenuated received feeble signal the biglyyest, it is difference input, difference output amplifier I that the present invention does not adopt dc bias circuit
1Two input end INP, INM the working point is provided.But adopt be and amplifier I at reset mode
1The electric capacity charging that links to each other of input end, be amplifier I with the electric charge that stores on the electric capacity
1Be provided at the direct current biasing of amplification mode.
Introduce a pair of reset switch K
1, K
2Realize amplifier I
1Switching between two patterns.K switch wherein
2Two ends respectively with amplifier I
1Normal phase input end INP link to each other K switch with reversed-phase output OUTM
1Two ends respectively with amplifier I
1Inverting input INM link to each other with positive output end OUTP.This semiconductor fingerprint extracting device 60 is operated in reset mode when switch closure, by amplifier I
1For with amplifier I
1The electric capacity charging that links to each other of input end INP, INM; This sensor array element circuit working is stored in and amplifier I at amplification mode when switch disconnects
1The electric capacity that links to each other of input end INP, INM on electric charge be amplifier I
1Dc point is provided.
Adopt the amplifier I of difference input, difference output
1Be in order to utilize characteristics such as this class A amplifier A high s/n ratio, high cmrr.The structure of the present invention and the mode of operation that resets can greatly reduce amplifier I
1The error effect that offset voltage brought of self.
Semiconductor fingerprint extracting device of the present invention can be used as a pixel cell of fingerprint image sensor integrated circuit.In order to obtain high resolving power, this fingerprint extracting device need take quite little area during as a pixel cell; And, need make capacitor C in order to obtain high signal to noise ratio (S/N ratio)
SValue as far as possible big, just make the area of battery lead plate big as far as possible.Among the present invention,, the partial circuit 61 of semiconductor fingerprint extracting device 60 is placed the below of battery lead plate 30 in order to make the entire device compact conformation.The signal of amplified signal level 45 outputs is through follow-up output circuit I
2And mould/number conversion circuit I
3, as shown in Figure 4, finally, supply with identification circuit and realize fingerprint recognition with the form output of digital signal.
Of the present invention one big characteristics have been to use the both-end amplifier, have the characteristic of high cmrr; Another advantage of the present invention is brought by introducing reset switch in the structure, and it can offset the offset voltage of amplifier.Above-mentioned advantage has greatly promoted the performance of this semiconductor fingerprint extracting device.
Description of drawings
Fig. 1 is the simplification longitudinal sectional drawing of first embodiment of semiconductor fingerprint extracting device of the present invention;
Fig. 2 is the simplification longitudinal sectional drawing of first embodiment of the semiconductor fingerprint extracting device that has a circuit connecting relation of the present invention;
Fig. 3 is the simplified electrical circuit diagram of semiconductor fingerprint extracting device first embodiment of the present invention;
Fig. 4 is the simplified electrical circuit diagram that has output circuit of first embodiment of the invention;
Fig. 5 is the simplification longitudinal sectional drawing of second embodiment of semiconductor fingerprint extracting device of the present invention;
Fig. 6 is the simplification longitudinal sectional drawing of the 3rd embodiment of semiconductor fingerprint extracting device of the present invention;
Fig. 7 is the simplified electrical circuit diagram with the corresponding integrated circuit of Fig. 6.
Embodiment
Hereinafter pass through some specific embodiments, and conjunction with figs., the present invention is described in further detail.
In these embodiments, with the pixel cell of semiconductor fingerprint extracting device of the present invention as the fingerprint image sensor integrated circuit.
As shown in Figure 1, be the simplification longitudinal sectional drawing of an embodiment of semiconductor fingerprint extracting device of the present invention.The figure middle finger shows the surface 11 of semiconductor fingerprint extracting device 60, is high rigidity of the present invention, wear-resistant, corrosion resistant protective seam 10 below this surface 11.The top on the surface 11 of device 60 is that the user points a part of 50 by being pressed on the fingerprint sensor among the figure.The part that the skin of finger 50 is pasting sensor surface 11 is a ridge 51, and the recessed part that gets on do not pasting sensor surface 11 is a paddy 52.In the drawings the left side with the finger 50 contacted be drive electrode 20a of the present invention, this drive electrode 20a with by be subjected to 21 control K switch
SWith signal source V
S Link.Drive electrode 20a conducts to signal on user's the finger 50.The below of protective seam 10 has marked four pole plates that are made of metal level in the drawings: induction pole plate 30, upper strata shielding pole plate 32, lower floor's shielding pole plate 31, lower floor's reference point pole plate 33.The partial circuit 61 of semiconductor fingerprint extracting device is placed in four metal polar plate belows.What draw below figure is the silicon substrate 12 of integrated circuit.Among the figure the below marked semiconductor fingerprint extracting device 60 of the present invention as a pixel cell shared space on integrated circuit.To exceed in thousand, ten thousand semiconductor fingerprint extracting device of the present invention and line up a two-dimensional array, just can catch the image of user's finger print, certainly, drive electrode 20a of the present invention and with the joining signal source V of this drive electrode 20a
SCan be shared.
Be the simplification sectional view that the present invention has first embodiment of circuit connecting relation further shown in figure 2.Design is placed with the amplifier I of a difference input, difference output under four pole plates that are made of metal level just having narrated
1With a pair of reset switch K
1, K
2The amplifier I of difference input, difference output
1Two input end INP, INM link to each other with two input ends 41,40 of amplified signal level respectively; The amplifier I of difference input, difference output
1Two output terminal OUTP, OUTM link to each other with two output terminals 42,43 of amplified signal level respectively.The partial circuit 61 of semiconductor fingerprint extracting device is placed the below of induced electricity pole plate 30, and this just makes that also induction pole plate 30 is subjected to the interference of circuit other parts easily.One with the sizable lower floors of induction pole plate 30 shielding pole plates 31 be placed in induction pole plate 30 under, lower floor is shielded pole plate 31 ground connection (it can be the signal ground or the power supply ground of system, also can be virtually), in order to overcome interference problem.
There are a relatively large stray capacitance C in induction pole plate 30 and 31 on lower floor's shielding pole plate
P1, the internal amplifier I that makes difference input, difference output
1Two input end INP, INM unbalance, this can reduce this amplifier I
1The accuracy of work.Present embodiment has been introduced upper strata shielding pole plate 32 and lower floor's reference point pole plate 33, has a stray capacitance C between these two pole plates
P2, lower floor's reference point pole plate 33 is connected to difference input, difference output amplifier I
1Another input end INM.If C
P1With C
P2The appearance value suitable, difference input, difference output amplifier I
1Two input end INP, INM just obtained the condition of balance work.
Upper strata shielding pole plate 32 is adjacent at grade with induction pole plate 30, upper strata shielding pole plate 32 links to each other with ground, and (it can be the signal ground or the power supply ground of system, also can be one virtually), in order to shielding from the signal on finger 50 surfaces to the influence of lower floor's reference point pole plate 33.Lower floor's reference point pole plate 33 be in upper strata shielding pole plate 32 under, adjacent with lower floor shielding pole plate 31 on same plane.
The user points 50 skin and the induction pole plate 30 of semiconductor fingerprint extracting device 60 has constituted capacitor C
SThe two poles of the earth, protective seam 10 and air are capacitor C
SThe insulation course of two interpolars.Think that here the skin surface of whole finger is equipotential, that is to say capacitor C
STop crown by be subjected to 21 control K switch
SWith signal source V
SLink.Stray capacitance C
P1 Shielding pole plate 31 by induction pole plate 30 with lower floor constitutes; Stray capacitance C
P2Constitute by upper strata shielding pole plate 32 and lower floor's reference point pole plate 33.The amplifier I of difference input, difference output
1Normal phase input end INP with the induction pole plate 30 link to each other; Amplifier I
1Inverting input INM link to each other with lower floor reference point pole plate 33.A pair of reset switch K
1, K
2Suspension control signal PRE_CHG control.Wherein, reset switch K
1Two ends respectively with amplifier I
1Inverting input INM link to each other with positive output end OUTP; Reset switch K
2Two ends respectively with amplifier I
1Normal phase input end INP link to each other with reversed-phase output OUTM.
Principle of work of the present invention for convenience of explanation, Fig. 3 has provided the simplification circuit theory diagrams of first embodiment of the invention.As reset switch K
1, K
2Closure, amplifier I
1Two output terminal OUTP, OUTM respectively to capacitor C
S, C
P1, C
P2Charging; As reset switch K
1, K
2During disconnection, be stored in capacitor C
S, C
P1, C
P2The electric charge at two ends is amplifier I
1Two input end INP, INM provide direct current biasing, amplifier I
1Work in amplification mode.As can be seen from the figure, as reset switch K
1, K
2During disconnection, amplifier I
1Two input end INP, INM do not have DC channel, like this design be in order to obtain high input impedance.Another advantage of this structural design is that it can self-adaptation adjust amplifier I
1The error that self offset voltage brought.
Under amplification mode, K switch
SClosure, signal source V
SProvide a signal delta v, capacitor C
SWith C
P1The polyphone dividing potential drop is at amplifier I
1Input end INP, produce signal delta V
In:
Formula 1
Then obtain differential output signal V
OUT:
v
OUT=v
OUTP-v
OUTM=A Δ v
InFormula 2
Wherein, A is amplifier I
1Voltage gain.
When by be pressed on the induction pole plate 30 be ' ridge ' time, capacitance C
SMaximum, output signal V
OUTMaximum; On by the surface 11 that is pressed in this sensor be ' during paddy, capacitance C
SMinimum, output signal V
OUTMinimum.Output signal V
OUTThe variation of size variation reflection finger print ' ridge ' and ' paddy '.
Shown in Figure 4 is the simplified electrical circuit diagram that first embodiment of the invention adds output circuit.Output signal V
OUTThrough output circuit I
2After the processing, again by DAC analog to digital conversion circuit I
3Convert digital signal output to.
Fig. 5 is the simplification longitudinal sectional drawing of second embodiment of fingerprint extracting device of the present invention.Compare with first embodiment, the difference of second embodiment shown in Figure 5 mainly contains two: first is the straightforward and signal source V of drive electrode 20b wherein
SLink; Second is that drive electrode 20b is that electrode by IC interior constitutes.This inner electrode not protected seam 10 covers fully, can contact straight with user's finger 50.This inner electrode can be the contact that is distributed in diverse location, or metal wire, also can be latticed.Principle of work is similar to first embodiment of the invention.
Fig. 6 is the simplification longitudinal sectional drawing of the 3rd embodiment of fingerprint extracting device of the present invention; Compare with second embodiment shown in Figure 5, difference has only one: drive electrode 20C is that the electrode by IC interior constitutes, and this inner electrode protected seam 10 covers fully.Like this, drive electrode 20C and user's finger 50 has constituted another capacitor C
DRVSignal source is passed through capacitor C
DRVSignal is conducted finger 50 to the user.
Fig. 7 is the simplified electrical circuit diagram with the corresponding integrated circuit of Fig. 6.Owing to introduced capacitor C among this figure
DRV, signal delta V
InBe for conversion into:
Formula 3
Obviously in the 3rd embodiment, amplifier I
1The signal of input end is because capacitor C
DRVIntroducing and reduced.
Although the present invention has done detailed explanation and quoted optimum example as proof,, obviously can make all replacement schemes, modification and change according to above-mentioned explanation for those of ordinary skill in the art.Therefore, all these replacement schemes, correction and change all should be included within the spirit and scope of claim.