CN105510985A - Mobile phone detection gate signal processing system - Google Patents

Abstract

The invention belongs to the technical field of mobile phone detection, and specifically relates to a mobile phone detection gate signal processing system. The mobile phone detection gate signal processing system described in the invention adopts a closed loop structure. The gain of the integral amplification link on a forward channel can be regarded to be infinite. A sensor probe actually works under the condition of 'zero magnetic field'. A magnetic field produced by feedback current and the environmental magnetic field are equal in size and opposite in direction. The signal gradient of the whole system mainly depends on the size of the feedback coefficient, and the whole system is of good linearity. Because of the characteristic of digital logic, the FPGA-based system has excellent temperature stability and portability and is easy to miniaturize compared with an analog system.

Description

Mobile phone detection door signal processing system

Technical field

The invention belongs to mobile phone detection technique field, be specifically related to a kind of mobile phone detection door signal processing system.

Background technology

Increasing secure locations needs to investigate for address list sound function equipment such as mobile phones, and mobile phone detecting gate arises at the historic moment.Existing mobile phone detecting gate is mainly divided into active and passive type two kinds.Active mobile phone detecting gate have employed the eddy current principle of metal detection door, and shortcoming is that electromagnetic radiation exceeds standard, and cannot get rid of key, the wrong report of the metal objects such as belt.Passive type mobile phone detecting gate then mainly adopts fluxgate sensor technology, coordinates certain software intelligence algorithm to improve accuracy rate, and to human-body safety without any radiation.Fluxgate sensor is generally used for the weak Magnetic testi of static state or low frequency variations, has sensitivity and reliability that other magneto sensors are difficult to match in excellence or beauty, is applicable to the detection of earth magnetism or human magnetic field.

The second harmonic that the output of fluxgate magnetic core mainly encourages, needs it to be transformed into the d. c. voltage signal linear with tested magnetic field.Traditional fluxgate signal processing circuit mainly adopts analog component, and make complicated, cost is high, and is difficult to miniaturization, and portability is also very poor.And under open loop approach, because iron core magnetic conductance variation with temperature is very large, the change of sensitivity of fluxgate is also very large, and temperature performance is easily influenced, and interference free performance is bad, and measuring accuracy is low, can not meet applied environment and the market demand of mobile phone detection door.

Summary of the invention

(1) technical matters that will solve

The technical problem to be solved in the present invention is: in order to improve measuring accuracy and the properties of product of mobile phone detection door, how to provide a kind of mobile phone detection door signal digital disposal system based on FPGA.

(2) technical scheme

For solving the problems of the technologies described above, the invention provides a kind of mobile phone detection door signal processing system, it comprises: sensor excitation source module, fluxgate signal condition acquisition module, negative feedback loop module;

Described sensor excitation source module comprises and is implemented in sinusoidal excitation circuit for generating in FPGA and outside DAC unit;

Described fluxgate signal condition acquisition module comprises outside high-speed ADC unit, and is implemented in AD interface unit, frequency-selecting amplifying unit, the phase depending on rectification unit in FPGA;

Described negative feedback loop module comprises integrator, D/A interface unit, high-speed DAC unit, and feedback network;

Described outside high-speed ADC is used for the simulating signal of fluxgate sensor to be converted to digital signal;

AD interface unit in the described FPGA of being implemented in is for converting serial data to parallel data;

Described selective frequency amplifier circuit is for selecting the second harmonic of sensor output signal and amplifying;

Described phase-sensitive rectifier circuit is used for the second-harmonic conversion after by amplification and becomes d. c. voltage signal, and suppresses or eliminate the impact of odd harmonic and DC component garbage signal;

Described negative feedback module adopts the closed-loop measuring circuit of high Open loop gain cofficient to obtain good linear output signal, and improves the stability of zero point and sensitivity; Wherein, signal carries out DA conversion after integrator integration, is sent back to the measuring coil of sensor by feedback network, ensures that sensor is in zero magnetic field working method, and the output of integrator is exactly the voltage signal linear with tested magnetic field.

(3) beneficial effect

The mobile phone detection door signal processing system described in the present invention adopts closed loop configuration, the gain of forward path upper integral amplifying element can be considered infinitely great, under condition that in fact sensor probe is operated in " zero magnetic field ", the magnetic field that feedback current produces is contrary with environmental magnetic field equal and opposite in direction direction.The Signal gradient of whole system depends primarily on the size of feedback factor, has the good linearity.Due to Digital Logic, compare with simulation system, the design based on FPGA has outstanding temperature stability, portable, and is easy to miniaturization.

Accompanying drawing explanation

Fig. 1 is technical solution of the present invention principle schematic.

Embodiment

For making object of the present invention, content and advantage clearly, below in conjunction with drawings and Examples, the specific embodiment of the present invention is described in further detail.

For solving the problem of prior art, the invention provides a kind of mobile phone detection door signal processing system, it comprises: sensor excitation source module, fluxgate signal condition acquisition module, negative feedback loop module;

As shown in Figure 1, described sensor excitation source module comprises and is implemented in sinusoidal excitation circuit for generating in FPGA and outside DAC unit;

Described fluxgate signal condition acquisition module comprises outside high-speed ADC unit, and is implemented in AD interface unit, frequency-selecting amplifying unit, the phase depending on rectification unit in FPGA;

Described negative feedback loop module comprises integrator, D/A interface unit, high-speed DAC unit, and feedback network;

Described outside high-speed ADC is used for the simulating signal of fluxgate sensor to be converted to digital signal;

AD interface unit in the described FPGA of being implemented in is for converting serial data to parallel data;

Described selective frequency amplifier circuit is for selecting the second harmonic of sensor output signal and amplifying;

Described phase-sensitive rectifier circuit is used for the second-harmonic conversion after by amplification and becomes d. c. voltage signal, and suppresses or eliminate the impact of odd harmonic and DC component garbage signal;

Described negative feedback module adopts the closed-loop measuring circuit of high Open loop gain cofficient to obtain good linear output signal, and improves the stability of zero point and sensitivity; Wherein, signal carries out DA conversion after integrator integration, is sent back to the measuring coil of sensor by feedback network, ensures that sensor is in zero magnetic field working method, and the output of integrator is exactly the voltage signal linear with tested magnetic field.

The mobile phone detection door signal processing system described in the present invention adopts closed loop configuration, the gain of forward path upper integral amplifying element can be considered infinitely great, under condition that in fact sensor probe is operated in " zero magnetic field ", the magnetic field that feedback current produces is contrary with environmental magnetic field equal and opposite in direction direction.The Signal gradient of whole system depends primarily on the size of feedback factor, has the good linearity.Due to Digital Logic, compare with simulation system, the design based on FPGA has outstanding temperature stability, portable, and is easy to miniaturization.

The present invention is described in detail below in conjunction with specific embodiment.

Embodiment 1

In the present embodiment, passive type mobile phone detecting gate adopts magnetic flux residual in fluxgate sensor technology detection communication sound pick-up outfit, and distinguish measured object according to characteristics of geomagnetic field distribution, thus reach the investigation to equipment to be checked.Thus, the present embodiment provides a kind of sensor signal processing circuit, and its basic structure as shown in Figure 1.

The technical scheme of the present embodiment functionally comprises: sensor excitation source module, fluxgate signal condition acquisition module, negative feedback loop module.Sinusoidal excitation circuit for generating in FPGA forms sensor excitation source module together with outside DAC.A/D interface in high-speed ADC and FPGA, frequency-selecting amplification, phase depending on rectification form fluxgate signal condition acquisition module.Integration amplification, D/A interface, high-speed DAC, and feedback network together constitutes negative feedback module.

During system works, under the driving of pumping signal, the inductive coil induced environment magnetic field size of fluxgate magnetic core, produces fluxgate signal, through converting by high-speed ADC chip the process that serial data send FPGA to after straight filtering.In FPGA, the serial data that ADC chip collects first converts parallel data to, is then amplified by frequency-selecting, obtains direct current signal after phase depending on rectification.After integration amplifies, become serial data to deliver to high-speed DAC chip through D/A interface conversion again to convert simulating signal to, feed back to the compensating coil of fluxgate magnetic core through feedback resistance, offset environmental magnetic field.

The fluxgate sensor of the present embodiment adopts three axis fluxgate sensors, can measure magnetic field size, again can direction of measurement.Fluxgate pumping signal exports sinusoidal digital signal by FPGA and produces, and frequency is about 5kHz, and the work clock of FPGA is 50MHz, and speed is relatively low, and accuracy requirement is not high, therefore DAC adopts 12 parallel port DA1210 chips.In this design, fpga chip selects the EP3C40F484C6 of ALTERA company CYCLONE III series, and operating rate is fast, and definable pin enriches, and number of logic cells is considerable, and cost performance is high.

In the forward path of closed-loop system, A/D module is separate-blas estimation link, exports sample to sensor probe.In this design, second harmonic one-period adopts 150 points, and namely ADC sample frequency is 150 times that probe exports second harmonic frequency, i.e. 1500kHz.Adopt AD7760 chip as A/D converter, this chip has 24 precision, and slewing rate is up to 2.5MSPS, can meet the demands.

In the feedback loop, D/A module is as compensation tache, and the present embodiment adopts AD5791 chip, has the switching rate of 20 precision and 35MSPS.

The excitation of FPGA internal sine occurs to adopt the mode of tabling look-up to realize.Fluxgate signal condition is the function that in FPGA, Digital Logic is most crucial with gathering, by Finite Impulse Response filter, and phase-sensitive rectifier and reference generator three part composition.

Phase-sensitive rectifier is made up of data converter and data selector.Data converter converts input to complement form, and data selector is selected to export input value or its complement code.Reference generator provides reference signal for phase-sensitive rectifier.Integration amplification is realized by integrator, in order to prevent overflowing, adopts totalizer and the register of 48.In closed-loop system, low 24 of integrator output is the digital quantity reflecting tested magnetic field size.

The above is only the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, under the prerequisite not departing from the technology of the present invention principle; can also make some improvement and distortion, these improve and distortion also should be considered as protection scope of the present invention.

Claims (1)

1. a mobile phone detection door signal processing system, is characterized in that, it comprises: sensor excitation source module, fluxgate signal condition acquisition module, negative feedback loop module;

Described sensor excitation source module comprises and is implemented in sinusoidal excitation circuit for generating in FPGA and outside DAC unit;

Described fluxgate signal condition acquisition module comprises outside high-speed ADC unit, and is implemented in AD interface unit, frequency-selecting amplifying unit, the phase depending on rectification unit in FPGA;

Described negative feedback loop module comprises integrator, D/A interface unit, high-speed DAC unit, and feedback network;

Described outside high-speed ADC is used for the simulating signal of fluxgate sensor to be converted to digital signal;

AD interface unit in the described FPGA of being implemented in is for converting serial data to parallel data;

Described selective frequency amplifier circuit is for selecting the second harmonic of sensor output signal and amplifying;

Described phase-sensitive rectifier circuit is used for the second-harmonic conversion after by amplification and becomes d. c. voltage signal, and suppresses or eliminate the impact of odd harmonic and DC component garbage signal;

Described negative feedback module adopts the closed-loop measuring circuit of high Open loop gain cofficient to obtain good linear output signal, and improves the stability of zero point and sensitivity; Wherein, signal carries out DA conversion after integrator integration, is sent back to the measuring coil of sensor by feedback network, ensures that sensor is in zero magnetic field working method, and the output of integrator is exactly the voltage signal linear with tested magnetic field.