CN103840853B - Be applicable to the automatic impedance matching circuit of radio-frequency SIM card - Google Patents
Be applicable to the automatic impedance matching circuit of radio-frequency SIM card Download PDFInfo
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- CN103840853B CN103840853B CN201410120738.1A CN201410120738A CN103840853B CN 103840853 B CN103840853 B CN 103840853B CN 201410120738 A CN201410120738 A CN 201410120738A CN 103840853 B CN103840853 B CN 103840853B
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Abstract
Be applicable to an automatic impedance matching circuit for radio-frequency SIM card, comprise local oscillator, SIM card antenna, capacitor matching network, start-oscillation circuit, buffer circuit and sampling and counting circuit, capacitor matching network passes through V after being connected with SIM card antenna
aand V
bnode is connected with the input of described buffer circuit, and start-oscillation circuit is connected across V
aand V
bbetween node, the output termination sampling of buffer circuit and the first input end of counting circuit; The sampling described in output termination of local oscillator and the second input of counting circuit, sampling is connected with the control end of capacitor matching network through start-oscillation circuit with the output of counting circuit.The present invention overcomes radio-frequency SIM card and is placed on when using in different mobile phone, the acute variation of SIM card antenna inductance value, stablizes signal transmitting and receiving during radio-frequency SIM card work; Same radio-frequency SIM card can use in different mobile phones, reduces complexity and the risk of error of chip design.
Description
Technical field
The present invention relates to application-specific integrated circuit (ASIC), particularly a kind of automatic impedance matching circuit being applicable to mobile phone radio frequency SIM card.
Background technology
Radio-frequency SIM card is a kind of SIM cards of mobile phones being integrated with radio communication function, it is integrated with wireless communication chips on traditional SIM cards of mobile phones, and as hardware carrier, by the mode of brush mobile phone, realize the application such as identification, gate inhibition, certification, public transport and financial payment.In daily life, mobile phone is absolutely necessary personal mobile communication instrument, how the banking network of growing growth is bundled with individual mobile terminal, carry out nimble account inquiry and capital management, become a hot spot technology in recent years.Mobile phone radio frequency SIM card technique, as a kind of solution of individual mobile payment, is just receiving increasing concern.
With reference to figure 1, a typical radio-frequency SIM card 100 at least comprises SIM card antenna 101, contactless front end CLF(ContactlessFront ?End) chip 102 and security module SE(SecureElement) chip 103.Due on market today, mobile phone is of a great variety, and installation and the plug-in card mode of radio-frequency SIM card are not quite similar, and result in radio-frequency SIM card when working in mobile phone, its radio frequency environment difference is huge.The difference of radio frequency environment, the design for radio-frequency SIM card brings very large challenge, and wherein, a topmost content is when radio-frequency SIM card is placed in different mobile phone, the change of the antenna performance of radio-frequency SIM card.For circuit designer, in different mobile phone, the change of antenna performance, can with its inductance value L
antchange embody.Due to the resonance frequency impact the inductance and chip capacity can be subject to, as inductance value L from radio-frequency SIM card antenna to the Signal transmissions of CLF chip 102
antwhen changing in different mobile phones, by
the resonance frequency determined greatly can have influence on reception and the transmitting of signal in CLF chip 102, thus has influence on the communication success rate of radio-frequency SIM card, finally affects the experience of swiping the card of user.
Summary of the invention
The object of the present invention is to provide a kind of automatic impedance matching circuit being applicable to radio-frequency SIM card, automatic impedance matching circuit is increased in contactless front-end chip 102, in the power-up initializing stage of radio-frequency SIM card, impedance matching network is adjusted, adaptively tracking antenna inductance value L
antchange, when radio-frequency SIM card is used in different mobile phone, by
the resonance frequency determined is relatively stable, thus stablizes the tranception-quality of radiofrequency signal, improves the mobile phone adaptability of radio-frequency SIM card.
Technical solution of the present invention is as follows:
A kind of automatic impedance matching circuit being applicable to radio-frequency SIM card, comprise local oscillator and SIM card antenna, its feature is also to comprise capacitor matching network, start-oscillation circuit, buffer circuit and sampling and counting circuit, and described capacitor matching network passes through V after being connected with described SIM card antenna
aand V
bnode is connected with the input of described buffer circuit, and described start-oscillation circuit is connected across V
aand V
bbetween node, the sampling described in output termination of described buffer circuit and the first input end of counting circuit; The sampling described in output termination of described local oscillator and the second input of counting circuit, described sampling is connected through the control end of start-oscillation circuit with described capacitor matching network 201 with the output of counting circuit.
Utilize above-mentioned automatic impedance matching circuit automatically to carry out impedance matching algorithm, its feature is that the step of this algorithm is:
The LC resonant cavity of 1. described capacitor matching network and SIM card antenna composition produces oscillator signal, and this oscillator signal produces slow clock signal f by buffer circuit
slowsampling described in input and counting circuit first input end; The fast clock signal f that described local oscillator produces
fastsecond input of the sampling described in input and counting circuit; Described sampling and counting circuit are to fast clock signal f
fastwith slow clock signal f
slowsample and calculate, obtaining the relative fold relation N between fast clock and slow clock frequency
out, by count value N
outthe control end of described capacitor matching network is inputted through described start-oscillation circuit 206;
2. described capacitor matching network is by count value N
outcompare with desired value N, work as N
outduring-N=0, enter step 3.; Otherwise, by fast clock f
fastwith slow clock f
slowbetween multiple proportion N
out, increase or reduce the capacitance of capacitor matching network, return step 1.;
3. terminate the operation of impedance adjustment, now, the LC resonant network be made up of capacitor matching network and SIM card antenna will be operated near target frequency value.
Compared with prior art, the apparent benefit using automatic impedance matching circuit of the present invention to bring is:
Adjust capacitor matching network adaptively, overcome radio-frequency SIM card and be placed on when using in different mobile phone, the acute variation of SIM card antenna inductance value, stablize signal transmitting and receiving during radio-frequency SIM card work;
Same radio-frequency SIM card can use in different mobile phones.Even if terminal use needs to change mobile phone, also without the need to changing SIM card.
Operating in power up of automatic impedance matching of the present invention completes, and when radio-frequency SIM card normally works, does not introduce extra power consumption;
Because described local oscillator is existing circuit module in traditional C LF chip, therefore, automatic impedance matching circuit of the present invention can multiplexing existing radio-frequency SIM card designing technique to a certain extent, reduces complexity and the risk of error of chip design.
Accompanying drawing explanation
Fig. 1 is the System's composition of typical radio-frequency SIM card in prior art.
Fig. 2 is the automatic impedance matching circuit diagram that the present invention is applicable to radio-frequency SIM card.
Fig. 3 is the specific embodiment adopting automatic impedance matching circuit of the present invention.
Fig. 4 is in described specific embodiment, the adjustment algorithm that capacitance network Circuit tuning uses.
Embodiment
Below in conjunction with embodiment and accompanying drawing, the invention will be further described, but should not limit the scope of the invention with this.
With reference to accompanying drawing 2, described automatic impedance matching circuit at least includes capacitor matching network 201, start-oscillation circuit 202, buffer circuit 203, local oscillator 204, sampling and counting circuit 205 and capacitance network Circuit tuning 206.Wherein, capacitor matching network 201 is connected with SIM card antenna 101, and capacitor matching network 201 is connected with buffer circuit 203 by Va with Vb node; Start-oscillation circuit 202 applies excitation on Va and Vb node, and make the LC resonant cavity be made up of capacitor matching network 201 and SIM card antenna 101 produce oscillator signal, this oscillator signal, by after buffer circuit 203, produces slow clock signal fslow; Local oscillator 204 produces the higher fast clock signal ffast of a relative fslow frequency; Fast clock ffast enters and samples and counting circuit 205 together with slow clock fslow, and sampling and counting circuit 205, according to the result of sampling with count, obtain the relative fold's relation between fast clock and slow clock frequency, export count value Nout.Capacitance network Circuit tuning 206 judges the multiple proportion between fast clock ffast and slow clock fslow according to this output count value Nout, and as certificate, increases or reduce the capacitance of capacitor matching network 201, until count value Nout is equal with the desired value preset.When described automatic impedance matching circuit power cut-off, the LC resonant network be made up of capacitor matching network 201 and SIM card antenna 101 will be operated near target frequency value.
With reference to accompanying drawing 3, in a specific embodiment, described automatic impedance matching circuit is formed in the following way.
Matching capacitance C
1301, C
2302 ... C
n303, switch S
1304, S
2305 ... S
n306.Matching capacitance C
1301 and switch S
1304 series connection, C
2302 and S
2305 series connection ... C
n303 and S
n306 series connection.Electric capacity C
1301, C
2302 ... C
nthe capacitances of 303 etc. are large, are C
0.The above-mentioned combination by capacitive series switch, receives the two ends V of SIM card antenna 101 each other in parallel
aand V
b, constitute the capacitor matching network in the present embodiment.V herein
aand V
bnode, is the V in accompanying drawing 2
aand V
bnode.P type metal-oxide-semiconductor M
p1307, P type metal-oxide-semiconductor M
p2308, N-type metal-oxide-semiconductor M
n1309, N-type metal-oxide-semiconductor M
n2310, tail current source I
s311.Wherein, M
p1the source of 307 connects power supply, M
p1the same M of grid end of 307
p2the drain terminal of 308 together, is connected to V jointly
bnode; M
p2the source of 308 connects power supply, M
p2the same M of grid end of 308
p1the drain terminal of 307 together, is connected to V jointly
anode; M
n1the same M of grid end of 309
n2the drain terminal of 310 together, is connected to V jointly
bnode; M
n2the same M of grid end of 310
n1the drain terminal of 309 together, is connected to V jointly
anode; M
n1the same M of source of 309
n1the source of 310 together, is connected to tail current source I jointly
s311.Above-mentioned four metal-oxide-semiconductors and tail current source, and the interconnection line between them, together constitute the start-oscillation circuit in the present embodiment.
P type metal-oxide-semiconductor M
p3312, P type metal-oxide-semiconductor M
p4313, N-type metal-oxide-semiconductor M
n3314, N-type metal-oxide-semiconductor M
n4315.Wherein, M
p3the source of 312 connects power supply, M
p3the grid end of 312 connects V
anode; M
p4the source of 313 connects power supply, M
p4the grid end of 313 connects V
bnode; M
n3the source of 314 is connected to ground, M
n3the grid end of 314 with drain terminal together, common and M
p3the drain terminal of 312 is connected; M
n4the source of 315 is connected to ground, M
n4the grid end M of 315
n3the grid end of 314 links together, M
p4the same M of drain terminal of 313
n4the drain terminal of 315 links together.Above-mentioned four metal-oxide-semiconductors, and the interconnection line between them, together constitute the buffer circuit in the present embodiment.The output of buffer circuit is M
p4the drain terminal of 313 and M
n4the circuit node that the drain terminal of 315 is connected together.
First frequency divider 316, second frequency divider 317, band edge triggers the accumulator 318 of Protection Counter Functions, and hereinafter referred to as accumulator, D type data buffer 319, hereinafter referred to as buffer.Wherein, the output being input as buffer circuit of the first frequency divider 316, i.e. slow clock signal f
slow, the clearing reset terminal Rst of accumulator 318 and the input end of clock Ck of buffer 319 are received in the output of the first frequency divider 316; The output being input as local oscillator 204 of the second frequency divider 317, fast clock signal f
fast, the input end of clock Ck of accumulator 318 is received in the output of the second frequency divider 317.The output S of accumulator 318
0, be connected to the input D of buffer 319.Above-mentioned first frequency divider 316, second frequency divider 317, accumulator 318 and buffer 319, and the interconnection line between them, together constitute the sampling in the present embodiment and counting circuit.The Q end of buffer exports, and is count value N
out.
Capacitance network Circuit tuning 320, it is input as count value N
out, it exports as W
1, W
2w
n, n road altogether.W
1, W
2w
nfeed back in capacitor matching network, link switch S respectively
1304, S
2305 ... S
n306, control these switch opens or closed according to capacitance network adjustment algorithm.
In the present embodiment, the specific works mode of described automatic impedance matching circuit is as follows.
When automatic match circuit in the present embodiment is started working, first by start-oscillation circuit to V
aand V
bnode applies excitation, and SIM card antenna and capacitor matching network form the resonant cavity of start-oscillation circuit jointly, at V
aand V
bnode producing a frequency is
oscillator signal.Wherein, C
matchfor capacitor matching network is at V
aand V
bthe total capacitance that node is seen, C
parafor V
aand V
bparasitic capacitance on node.Oscillator signal, through buffer stage, is exaggerated into the slow clock signal f that power supply expires the amplitude of oscillation with arriving
slow.Because buffer stage only changes the amplitude of oscillator signal, and do not change its frequency, the slow clock signal frequency that buffer stage exports is
first frequency divider 316 and the second frequency divider 317 have identical divide ratio, and they are by fast clock f
fastwith slow clock f
slowfrequency carry out equimultiple frequency division, entirety reduces operating frequency and the power consumption of accumulator, but does not change its judged result to multiple proportion between two clock frequencies.After accumulator 318 often detects a clock signal from Ck end, once+1 operation is done to its output valve Q, until after the rising edge of a pulse from Rst end being detected, export Q and be cleared.Clock signal due to buffer 319 is slow clock f
slow, the data that buffer is recorded are the maximums after accumulator carries out accumulated counts operation at every turn, i.e. round (f
fast/ f
slow), wherein round (*) is operator notation, represents floor operation.
In the capacitance network Circuit tuning 320 of the present embodiment, use capacitance network adjustment algorithm.With reference to figure 4, the embodiment of the capacitance network adjustment algorithm in described embodiment is as follows.
The first step, chooses electric capacity hunting zone (C
min, C
max) intermediate value
according to m value configuration capacitor matching network, by switch S
1~ S
mclosed, switch S
m~ S
nopen.Now, m shunt capacitance is introduced into resonant tank altogether, the capacitance C provided by capacitor matching network
match=mC
0.In above formula, C
min∈ [1, n-1], C
max∈ [2, n], especially, for first time adjustment, min=1, max=n.
Second step, according to selected C
match, start-oscillation circuit work, makes V
aand V
bnode produces oscillator signal, after buffer circuit, forms slow clock signal, its frequency
3rd step, sampling and counting circuit, according to the multiple proportion between fast clock and slow clock frequency, export count value N
out, m=round (f
fast/ f
slow, m).
4th step, compares N
out, mwith desired value N
narmalbetween magnitude relationship.
If N
out, m>N
narmal, illustrate that slow clock frequency is lower than desired value, the capacitance introducing capacitor matching network is bigger than normal, should reduce shunt capacitance, therefore, by the upper limit C of electric capacity hunting zone
maxassignment is C
m, lower limit C
minconstant, come back to the first step, start the operation of a new circulation; If N
out, m<N
narmal, illustrate that slow clock frequency is higher than desired value, the capacitance introducing capacitor matching network is less than normal, should increase shunt capacitance, therefore, by the lower limit C of electric capacity hunting zone
minassignment is C
m, upper limit C
maxconstant, come back to the first step, start the operation of a new circulation; If N
out, m=N
narmal, illustrate that the frequency of slow clock is close to desired value, records current m
final, as the result of capacitance network adjustment, terminate the adjustment of resistance match circuit automatically.
5th step, according to m
finaldetermine the form of capacitor matching network, switch S 1 ~ S
m, finalclosed, switch S
m, final~ S
nopen.The capacitance C of final introducing resonant tank
match, final=m
finalc
0.
Although the present invention illustrates as above by preferred embodiment, this preferred embodiment is also not used to limit the present invention.Those skilled in the art, without departing from the spirit and scope of the present invention, should have the ability make various correction to this preferred embodiment and supplement, therefore, protection scope of the present invention is as the criterion with the scope of claims.
Claims (2)
1. one kind is applicable to the automatic impedance matching circuit of radio-frequency SIM card, comprise local oscillator (204) and SIM card antenna (101), characterized by further comprising capacitor matching network (201), start-oscillation circuit (202), buffer circuit (203) and sampling and counting circuit (205), described capacitor matching network (201) passes through V after being connected with described SIM card antenna (101)
aand V
bnode is connected with the input of described buffer circuit (203), and described start-oscillation circuit (202) is connected across V
aand V
bbetween node, the sampling described in output termination of described buffer circuit (203) and the first input end of counting circuit (205); The sampling described in output termination of described local oscillator (204) and the second input of counting circuit (205), described sampling is connected through the control end of capacitance network Circuit tuning (206) with described capacitor matching network (201) with the output of counting circuit (205);
Described start-oscillation circuit (202) applies excitation on Va and Vb node, the LC resonant cavity be made up of capacitor matching network (201) and SIM card antenna (101) is made to produce oscillator signal, this oscillator signal, by after buffer circuit (203), produces slow clock signal fslow; Local oscillator (204) produces the higher fast clock signal ffast of a relative fslow frequency; Fast clock ffast enters sampling and counting circuit (205) together with slow clock fslow, sampling and counting circuit (205) are according to the result of sampling with count, obtain the relative fold's relation between fast clock and slow clock frequency, export count value Nout; Capacitance network Circuit tuning (206) judges the multiple proportion between fast clock ffast and slow clock fslow according to this output count value Nout, and as certificate, increase or reduce the capacitance of capacitor matching network (201), until count value Nout is equal with the desired value preset.
2. utilize the automatic impedance matching circuit described in claim 1 automatically to carry out the method for impedance matching, it is characterized in that the method is:
1. the LC resonant cavity that described capacitor matching network (201) and SIM card antenna (101) form produces oscillator signal, and this oscillator signal produces slow clock signal f by buffer circuit (203)
slowsampling described in input and counting circuit (205) first input end; The fast clock signal f that described local oscillator (204) produces
fastsecond input of the sampling described in input and counting circuit (205); Described sampling and counting circuit (205) are to fast clock signal f
fastwith slow clock signal f
slowsample and calculate, obtaining the relative fold's relation between fast clock and slow clock frequency, export count value N
out, through the control end of the capacitor matching network (201) described in the input of described start-oscillation circuit (206);
2. this capacitor matching network (201) is by count value N
outcompare with desired value N, work as N
out-during N=0, enter step 3.; Otherwise by fast clock f
fastwith slow clock f
slowbetween multiple proportion, increase or reduce capacitor matching network (201) capacitance, return step 1.;
3. terminate the operation of impedance adjustment, now, the LC resonant network be made up of capacitor matching network (201) and SIM card antenna (101) will be operated near target frequency value.
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