Abstract: First introduced the disturbance in based on the DSP pronunciation processing system’s harm, next analyzed has formed the disturbance the reason, finally proposed the corresponding antijamming technology, and has given the hardware antijamming technology and the software antijamming technology design proposal separately.
Key word: DSP; Voice signal; Electromagnetic interference; Electromagnetic compatibility
l introduction
At present, because has the operating speed to be quick, on the piece the fruitful in resources and can realize complex characteristics and so on linearity and misalignment algorithm, DSP has become domain and so on correspondence, computer and expense electronic products foundation components, appears in the voice signal processing technology aspect the outstandingly. However, because including the DSP itself all electronic device is the noise source, moreover the system locates in the working conditions also has the external noise source, in addition the speech recognition technology is sensitive to the signal noise, must therefore consider system’s antijamming question in the system design. Otherwise, will affect system’s processing result at least, will create a more serious consequence. This article introduces based on the DSP voice signal processing system’s antijamming technology.
2 system’s noise sources and disturbance way
The noise source which mainly has the atmospheric noise source which, the sun-spot movement based on the DSP voice signal processing system’s noise source the thunder discharge creates and so on to cause electronic primary devices and so on static noise source which, resistance works when gives off heat creates the thermal noise source which, 50 Hz power frequency electrical network to cause the electrical network noise source which, the domestic electric appliances creates the noise source which, the electrical machinery to cause the electronics brush noise source which, the automobile firing device creates the ignition system noise source which, the wireless communication system to create the radio frequency noise source which as well as some artificial evil intentions creates and so on, all noise source intermediate frequency impulse noise/pulse noise/pulsive noise is biggest to the digital signal processing system’s harm (here not to study acoustic jamming which pronunciation causes).
The above mentioned the noise source belongs to electromagnetic interference (EMI). Electromagnetics principle: So long as will have the electric current to exist will produce the magnetic field, so long as will have the voltage to exist will have the electric field. The magnetic field, the electric field along with time variation quantity’s how many, have the electromagnetic interference basic reason. Electromagnetic interference’s concept as shown in Figure 1.
Mainly has the power line, the input/output line based on the DSP voice signal processing system’s disturbance way, to meet the grounding, the electromagnetic induction, the electrostatic induction, electric circuit’s common impedance, the power source unusual and so on. Each disturbance way occupies in the system compares for example Table 1 to show.
3 antijamming measures
According to the system own, the noise source and the disturbance way’s analysis, the antijamming measure main plan is:
①Enhances the system own electromagnetic compatibility;
②Isolation noise source;
③Cut-off disturbance way.
Based on these 3 kind of plans, this article proposed some are suitable for this system’s hardware antijamming technology and the software antijamming technology.
3.1 electromagnetic compatibility
The electromagnetic compatibility is the beacon strength, the electron, the communication equipment or its system when its establishment’s place is at the active status, to its periphery does not have the influence, is also not affected by it electromagnetic environment all around, does not have the misoperation and the performance reduces, obtains its working ability according to the design. That is, the equipment or the system do not have the electromagnetic interference to the outside, moreover does not receive locates in the environment the electromagnetic interference to affect its normal work ability.
3.2 hardware antijamming technology
Because the radio impulse noise is biggest to this system harm, to enhance system’s resistance to interference, may take the following measure in the system:
(1) increases main line’s antijamming ability. Uses the three states of matter portal type-like bus structure, and joins to the main line pulls the resistance, causes the main line in instantaneous to be at the stable high level to avoid the main line having the hanging condition. The main line must add the buffer.
(2) sharpens the systems control signal antijamming ability. Usually has pilot wires and so on RESET, STB in the system, when CPU controls component’s transmitting range with it to be far, and the control line impedance is high time, easy to receive the impulse noise/pulse noise/pulsive noise disturbance. May in control component’s input end parallel 20 pF electric capacity, and so on controls the holding wire parallel 0.Ol μF electric capacity in RESET. The pilot wire adds the first-level buffer, causes pilot wire’s impedance changes low, is also helpful to the barrage jamming.
(3) suppresses the digital signal the string mold disturbance. This kind of string mold disturbance is the neighboring holding wire the disturbance which causes in the transmission signal process, mostly occurs in the board parallel wire. Strings together between the strong and the weak which and the neighboring two holding wire’s coupled impedance and signal’s impedance the mold disturbs concerns. Therefore, must reduce holding wire’s length as far as possible in this system; When transmits many kinds of level signals, the back edge time close level signal divides into a group to transmit before as far as possible; Arrange the big area in the two-sided board’s backs the grounding region, thus produces to the part the radio impulse noise plays the absorption and the shield role.
(4) (EMI Filter) eliminates the power source disturbance using the electromagnetic interference filter. Along with the electronic installation, the computer and domestic electric appliances’ massive emergences and the widespread popularization, the electrical network disturbance is being day by day serious and forms one kind of environmental damage. Specially transient state electromagnetic interference, its voltage amplitude high (several hundred volt supreme kilovolt), rise speed block, duration short, random, easy to cause the digital circuit to have the significant disturbance, even harms the equipment. The electromagnetic interference filter also said that power source noise filter (PNF), it can suppress the electrical network noise effectively, sharpens equipment’s antijamming ability and system’s reliability. Electromagnetic interference filter’s in system application as shown in Figure 2.
(5) sharpens system’s antijamming ability using the hardware watch-dog function. By special-purpose component MAX692 constitution’s watch-dog electric circuit as shown in Figure 3, the system uses the periphery part to be few. MAX692 is the micro system monitoring circuit, has reserve functions and so on battery cut, power failure distinction, watch-dog monitoring. And WDI is the watch-dog examination input end, receives DSP on a special-purpose I/O mouth or a main line mouth. RESET is the reset signal out-port, meets DSP the replacement to carry RST. The MAX692 WDI fixed time cycle is 1.6 s, the reset pulse width is 200 ms. If WDI maintains Gao Huodi surpasses “the watch-dog” fixed time the cycle (1.6 s), the RESET end will produce wide 200 ms (smallest 140 ms) negative pulse causes DSP to reposition.
3.3 software antijamming technology
May also sharpen the DSP pronunciation processing system’s antijamming ability using the software. Mainly has:
①Filters the disturbance using the digital filter;
②Uses the software watch-dog, the multiple sampling technique, fixed time technology barrage jammings and so on refurbishing outlet.
Below main introduction digit filter’s in this system application.
Digital filter (DF) to voice signal’s treating processes as shown in Figure 4. The voice signal first/maintains after the sampling the electric circuit (S/H), delivers transforms the digital quantity to mold/number switch (ADC), then through the digital filter filtration unwanted signal, obtains the voice signal output finally through number/mold switch (DAC).
According to uses the mathematical model the difference, the digital filter to be possible to divide into two broad headings: One kind is the recursion filter, its characteristic is filter’s output not only with the input signal related, moreover also with past value of exports related; Another kind of right and wrong recursion filter (for example first-order, second-order low pass filter), its characteristic is filter’s output only with the input signal related, but had nothing to do with past value of exports. What this system use is the recursion filter.
Supposes the digital filter’s input signal is X(n), the output signal is Y(n), then between the list entries and output sequence’s relations available difference equation expression is:
The digital sequence which in the above equation, input signal X(n) may be the voice signal transforms after the sampling and ADC obtains, may also be computer’s output signal; ak and bk are coefficients, through establishes ak and bk may the bandpass filter which designs DF needs.
The digital filter’s software design method includes: After procedure judgment filtering (restriction filtering), position value filtering, arithmetic mean filtering, recursion average filtering, against pulse interference average filtering, first-order, filtering and so on 6 methods. According to the need, this system selection program judgment filtering, design cycle as shown in Figure 5.
4 concluding remark
The experiment proved: The above antijamming method in can suppress fully based on the DSP voice signal processing system from system’s outside disturbance, sharpens system’s antijamming ability and the reliability effectively.
