CN100576239C

CN100576239C - The self-adaptive threshold demodulation circuit that is used for non-contact IC card or RFID tag

Info

Publication number: CN100576239C
Application number: CN200610026566A
Authority: CN
Inventors: 刘曙斌
Original assignee: Shanghai Huahong Integrated Circuit Co Ltd
Current assignee: Shanghai Huahong Integrated Circuit Co Ltd
Priority date: 2006-05-15
Filing date: 2006-05-15
Publication date: 2009-12-30
Anticipated expiration: 2026-05-15
Also published as: CN101075296A

Abstract

The invention discloses a kind of self-adaptive threshold demodulation circuit.Described demodulator circuit comprises the current generating circuit that detects incoming signal level, the threshold value generative circuit that utilizes demodulation output Control current to flow to, and differential comparator.Described current generating circuit produces and is proportional to the electric current of incoming signal level and sends into described threshold value generative circuit, produces one along with incoming signal level raises and the big threshold value of self-adaptation change.Described differential comparator utilizes this threshold value to finish demodulation to input signal.The present invention can adjust the demodulation threshold of demodulator circuit adaptively, has certain noise resisting ability, improves demodulation performance, the expansion working range.Be applicable to non-contact IC card or RFID tag.

Description

The self-adaptive threshold demodulation circuit that is used for non-contact IC card or RFID tag

Technical field

The present invention relates to a kind of demodulator circuit, particularly relate to a kind of self-adaptive threshold demodulation circuit that is used for non-contact IC card or radio frequency identification label chip.

Background technology

Along with the development of radio frequency and integrated circuit technique, non-contact IC card or RFID tag just progressively replace traditional paper ticket and are widely used in industries such as subway, public transport, authentication, logistics.

Non-contact IC card or radio frequency identification label system comprise read write line and non-contact IC card or radio frequency identification label chip two parts.

Fig. 1 shows to finishing normal communication between read write line and non-contact IC card or the RFID tag, non-contact IC card or the needed functional circuit of RFID tag internal radio frequency interface.Wherein, the AC signal that rectification and limit filtration circuit are come the antenna end coupling on the one hand changes the direct current signal through limit filtration into, send into follow-up mu balanced circuit and demodulator circuit then and handle, by the mode of load-modulate logical signal d_in is launched on the other hand.Clock generation circuit generates synchronous clock clk.Mu balanced circuit produces burning voltage vdd and powers to internal circuit.Reset circuit produces reset signal por according to the height of voltage vdd.Demodulator circuit recovers read write line transmission data d_out by the detection to envelope signal.

Non-contact IC card or RFID tag need and can respond the signal that read write line sends in certain field strength range, field intensity difference of living in, the energy difference that antenna is coupled to, thereby the level that obtains after the rectifying and wave-filtering output will be different, and the depth of groove of envelope signal of sending into demodulator circuit is also different.Non-contact IC card or RFID tag field intensity of living in increases, and the described envelope signal depth of groove of sending into demodulator circuit is deepened, and it is big that the noise of signal also can become.If it is constant that the demodulation threshold of demodulator circuit remains, demodulator circuit just can not be realized the data demodulates in the whole field strength range well so, and noise resisting ability is also limited simultaneously.

Summary of the invention

The technical problem to be solved in the present invention provides a kind of demodulator circuit that is used for non-contact IC card or radio frequency identification label chip, it can adjust the demodulation threshold of demodulator circuit adaptively, have certain noise resisting ability, improve demodulation performance, the expansion working range.

In order to solve the problems of the technologies described above, the demodulator circuit that the present invention is used for non-contact IC card or radio frequency identification label chip comprises: the current generating circuit that detects incoming signal level, utilize the FEEDBACK CONTROL of demodulated output signal to flow through the threshold value generative circuit of the current direction of threshold resistance and differential comparator; Described current generating circuit produces and is proportional to the electric current of incoming signal level and sends into described threshold value generative circuit, produces one along with incoming signal level raises and the big threshold value of self-adaptation change by this threshold value generative circuit; Described differential comparator utilizes this threshold value to finish demodulation to input signal.

Owing to adopt circuit of the present invention, utilize the current direction of demodulated output signal FEEDBACK CONTROL threshold resistance to obtain demodulation threshold, strengthened the noise resisting ability of demodulator circuit.In addition, utilize feasible electric current and the proportional variation of demodulation input signal of flowing through threshold resistance of an operational amplifier, and then make demodulation threshold become big and become big, expanded the working range of non-contact IC card or RFID tag along with input signal.

Description of drawings

The present invention is further detailed explanation below in conjunction with accompanying drawing and embodiment:

Fig. 1 is the radio-frequency interface circuit theory diagram of non-contact IC card or radio frequency identification label chip;

Fig. 2 is the schematic diagram that the present invention is used for the self-adaptive threshold demodulation circuit embodiment of non-contact IC card or RFID tag.

Embodiment

The demodulator circuit that the present invention is used for non-contact IC card or radio frequency identification label chip comprises: detect the current generating circuit of incoming signal level, described input signal is the output signal of current rectifying and wave filtering circuit, and this signal changes along with the variation of field intensity.Described current generating circuit produces the electric current that is proportional to incoming signal level, this electric current is sent into the threshold value generative circuit that a FEEDBACK CONTROL of utilizing demodulated output signal flows through the current direction of threshold resistance, produces one by the threshold value generative circuit and raises along with incoming signal level and self-adaptation becomes big threshold value.Differential comparator utilizes described threshold value to finish demodulation to input signal.

Current generating circuit comprises an amplifier unit, and the partial pressure value of incoming signal level is followed in this amplifier unit, produces to follow signal, generates follow current, and this follow current is put on the threshold resistance of described threshold value generative circuit.

Described differential comparator is a zero-crossing comparator, and the positive input of this zero-crossing comparator is an end signal of described threshold resistance, and reverse input end then is the RC filtering output of described threshold resistance other end signal.Two input ends of described differential comparator come from the Vgs pressure drop of rectifying and wave-filtering output signal, and the time constant of described RC filtering equates with the communication data recess width substantially.

Shown in Figure 2 is a specific embodiment of the present invention.The interchange carrier signal that sends to the space when read write line produces output signal by the coupling of the antenna end of non-contact IC card or RFID tag and after sending into current rectifying and wave filtering circuit, i.e. direct current envelope signal DEM_IN.The height of this envelope signal DEM_IN is directly relevant with non-contact IC card or RFID tag field intensity of living in.Field intensity of living in is high more, and envelope signal DEM_IN is high more, and amplitude modulation depth is dark more; Field intensity of living in is low more, and envelope signal DEM_IN is low more, and amplitude modulation depth is shallow more.Described envelope signal DEM_IN is as the input of demodulator circuit, by obtaining voltage V3 behind the transistor MP3 reduction Vgs.Resistance R 2 one ends are V3, and an other end VI+ is then as the positive input of difference zero-crossing comparator COMP; Obtain the reverse input end of VI-after the RC filtering of V3 by resistance R 3 and capacitor C as difference zero-crossing comparator COMP.

When non-contact IC card or RFID tag enter field intensity and stable after, at first receive carrier signal, this moment, described envelope signal DEM_IN did not have groove.Before the strong stability on the scene, because the reverse input end VI-of comparator C OMP is the RC filtering output of V3, so VI-sets up the positive input VI+ that stable speed will be slower than comparator C OMP.VI+ is more stable than the first arrival of VI-, and VI+ is higher than VI-, and comparator C OMP is output as high level, and P transistor npn npn MP7 ends, so demodulation output D_OUT initial state is high.At this moment, feedback signal VFB1 is high, and VFB2 is low, by the feedback of feedback signal VFB1 and VFB2, and transistor MP6, MN6 conducting, transistor MP5, MN7 end.At this moment threshold resistance R2 goes up and exists by the electric current I th of VI+ to V3, guarantee that VI+ is all the time than the high threshold voltage vt h of V3 (Vth=R2*Ith), and VI-is the RC filtering of V3, D. C. value equals V3, therefore guarantee that the positive input terminal VI+ of comparator C MOP is higher than threshold voltage vt h of negative input end VI-all the time, plays the antinoise effect.When read write line sent the carrier signal of process amplitude modulation(PAM), described envelope signal DEM_IN produced a groove, and VI+ begins to descend along with the decline of described envelope signal DEM_IN immediately, and the VI-effect owing to RC filtering of holding keeps constant relatively.When VI+ changes to when lower than VI-, comparator C OMP overturns, comparator C OMP output becomes low, P transistor npn npn MP7 conducting, demodulation output D_OUT is low by hypermutation, at this moment, feedback signal VFB1 becomes low, VFB2 becomes height, by the feedback of feedback signal VFB1 and VFB2, transistor MP5, the MN7 conducting, transistor MP6, MN6 ends, threshold resistance R2 went up and existed by the electric current I th of V3 to VI+ this moment, guarantee VI+ all the time than the low threshold voltage vt h (Vth=R2*Ith) of V3, and VI-is the RC filtering of V3, D. C. value equals V3, therefore guarantee that the positive input terminal VI+ of comparator C MOP is lower than threshold voltage vt h of negative input end VI-all the time, plays the antinoise effect.

In addition, the present invention utilizes an amplifier unit to generate along with described envelope signal DEM_IN becomes big and electric current that increase, and send into demodulation threshold resistance R 2, the voltage at threshold resistance R2 two ends is that demodulation threshold is along with described envelope signal DEM_IN is that field intensity becomes big and strengthens the adaptive change of realization demodulation threshold.Transistor MN1, the MN2 of diode connection and MN3 are bleeder circuit, and when field intensity becomes big, described envelope signal DEM_IN raises, and V1 raises, and the effect by amplifier OPAMP and source follower MN4 makes V2 increase, and the electric current that flows through resistance R 1 strengthens; Effect by transistor MP1, MP2, MP4 and MN5, MN8 successively with this current mirror to transistor MP4 and MN8, like this, the electric current I th that flows through threshold resistance R2 becomes big, it is big that the pressure reduction at threshold resistance R2 two ends becomes, and promptly strengthened the demodulator circuit threshold value; In like manner, when field intensity diminishes, described envelope signal DEM_IN reduces, and V1 reduces, and the effect by amplifier OPAMP and source follower MN4 makes V2 decrease; The electric current that flows through resistance R 1 reduces, the effect by transistor MP1, MP2, MP4 and MN5, MN8 successively with this current mirror to transistor MP4 and MN8.Like this, the electric current I th that flows through threshold resistance R2 reduces, and the pressure reduction at threshold resistance R2 two ends diminishes, and has promptly reduced the demodulator circuit threshold value.And field intensity is big more, and the noise dither on the described envelope signal DEM_IN is just big more, and the demodulator circuit of this adaptive threshold also helps the raising of noise robustness.

As mentioned above, the present invention utilizes the method for current direction on the demodulation output control threshold resistance to finish the demodulation function of certain demodulation threshold by use, and make the electric current that flows through threshold resistance along with field intensity becomes big, the change that is described rectifying and wave-filtering output DEM_IN becomes big greatly, realized the self-adaptation adjustment of demodulation threshold, improve the noise resisting ability of demodulator circuit, expanded the working range of non-contact IC card or RFID tag simultaneously.

Claims

1, a kind of self-adaptive threshold demodulation circuit that is used for non-contact IC card or RFID tag, it is characterized in that, described demodulator circuit comprises: the current generating circuit that detects incoming signal level, utilize the FEEDBACK CONTROL of demodulated output signal to flow through the threshold value generative circuit of the current direction of threshold resistance and differential comparator; Described current generating circuit produces and is proportional to the electric current of incoming signal level and sends into described threshold value generative circuit, produces one along with incoming signal level raises and the big threshold value of self-adaptation change by this threshold value generative circuit; Described differential comparator utilizes this threshold value to finish demodulation to input signal.

2, the self-adaptive threshold demodulation circuit that is used for non-contact IC card or RFID tag as claimed in claim 1, it is characterized in that: current generating circuit comprises an amplifier unit, the partial pressure value of incoming signal level is followed in this amplifier unit, signal is followed in generation, generate follow current, and this follow current is put on the threshold resistance of described threshold value generative circuit.

3, the self-adaptive threshold demodulation circuit that is used for non-contact IC card or RFID tag as claimed in claim 1, it is characterized in that: described differential comparator is a zero-crossing comparator, the positive input of this zero-crossing comparator is an end signal of described threshold resistance, and reverse input end then is the RC filtering output of described threshold resistance other end signal.

4, the self-adaptive threshold demodulation circuit that is used for non-contact IC card or RFID tag as claimed in claim 3 is characterized in that: two input ends of described differential comparator come from the Vgs pressure drop of rectifying and wave-filtering output signal.

5, the self-adaptive threshold demodulation circuit that is used for non-contact IC card or RFID tag as claimed in claim 3 is characterized in that: the time constant of described RC filtering equates with the communication data recess width substantially.