CN102193106A - Method for generating frequency sweeping signal special for controllable seismic source - Google Patents

Abstract

The invention relates to a method for generating a frequency sweeping signal special for a controllable seismic source, which is characterized by comprising the steps: (1) programs in various waveforms are stored in a system consisting of DSP (Digital Signal Processor) chips by means of software presetting; (2) command parameters are input into the DSP chip system via an ARM (Advanced RISC Machines) development board; (3) a DSP completes the calculation of phase increment at an output sample point according to the set parameters and generates a amplitude corresponding to a waveform function, and then performs windowing on the amplitude; and (4) a DA (Digital-Analog) converter converts the calculation result into the output of an analog quantity, and finally obtains an eventual output analog signal via a low-pass filter. The method has the advantages that frequency synthesis is performed by means of the time-shared utilization of DSP and DAC (Digital-to-Analog Converter)-analog DDS chips, thus various waveforms required by the controllable seismic source can be generated, and real-time calculation and output of sample points are realized by adopting the high-speed DPS chips, thereby the demands of the controllable seismic source on the precision of frequency sweeping signals and the diversification of waveforms can be met.

Description

The production method of the special-purpose swept-frequency signal of a kind of vibroseis

Technical field:

The present invention relates to a kind of production method of swept-frequency signal, the production method of the special-purpose swept-frequency signal of particularly a kind of vibroseis belongs to signal source generating technique field.

Background technology:

At present, the composition proposal in common known signal source generally all is made of analog devices such as resistance, electric capacity, fortune sides, and the signal accuracy that it generated is low, and waveform is single.Also there is signal source to adopt microprocessor to cooperate parts such as the special-purpose DDS external DA of (Direct Digital frequency synthesis) chip (digital simulation) converter, wave filter to form in addition, though such composition proposal has improved precision, but still lack dirigibility, can not satisfy vibroseis the multifarious specific (special) requirements of signal.

Now in the vibroseis field, the mode of the employing signal storage that also has, being about to the instrument of needed sweep signal by special use is stored in the special-purpose storer in advance, call again when treating vibroseis work, but this working method needs to do a large amount of preliminary work before construction, operating cost is also higher.

Summary of the invention:

In order to overcome the deficiencies in the prior art, the object of the present invention is to provide the production method of the special-purpose swept-frequency signal of a kind of vibroseis, by software DDS scheme, the parameters that real-time setting is relevant with waveform with change, produce various types of swept-frequency signals, can satisfy vibroseis swept-frequency signal precision and the diversified requirement of waveform.

The present invention realizes above-mentioned purpose by following technical solution.

1, presets the program that in the system that constitutes by DSP (digital signal processor) chip, deposits various waveforms in by software.

2, by ARM (advanced reduced instruction machine) development board input command parameter in the dsp chip system, comprise signal type, initial frequency, end frequency, sweep time length, cascade scanning number of times, whether windowing, window function type, start, stop.

3, DSP finishes the computing of output sample phase increment according to the parameter that is provided with and generates and the corresponding amplitude of wave function, and then amplitude is carried out windowing process.

4, the DA converter then is converted to operation result the output of analog quantity, obtains final output simulating signal through a low-pass filter at last.

The present invention compared with prior art, its advantage is that timesharing utilizes DSP (digital signal processor) and DAC (digital to analog converter) analog D DS chip to carry out frequency synthesis, can generate the needed various waveforms of vibroseis, adopt dsp chip at a high speed, realize real-time computing and the output of sampling point, can satisfy vibroseis swept-frequency signal precision and the diversified requirement of waveform.

Description of drawings:

Fig. 1 is a systems solutions block diagram of the present invention.

Fig. 2 is SCI interface circuit figure.

Fig. 3 is low-pass filter circuit figure.

Fig. 4 is DSP and DA switching device interface circuit diagram.

Embodiment:

The present invention is further illustrated below in conjunction with drawings and Examples.

Fig. 1 systems solutions block diagram of the present invention.The man-machine interface of ARM among the figure (advanced reduced instruction machine) development board is used for realizing man-machine interface, on the ARM display screen, relevant parameters can be set, comprise length sweep time, scan type, initial scanning slope, whether windowing etc., the parameter after the setting passes to the dsp chip system by SCI (serial communication interface).The dsp chip system finishes the computing of output sample phase increment according to the parameter that is provided with and generates and the corresponding amplitude of wave function, and then amplitude is carried out windowing process.The DA converter then is converted to operation result the output of analog quantity, obtains final output simulating signal s (t) through a low-pass filter at last.

LCD (LCD) and keyboard can carry out the setting and the modification of parameter, to satisfy different user's requests.

The concrete sweep signal of implementing with CHIRP is an example, and other sweep signal output intents are identical with it.

The CHIRP signal has metastable amplitude, and signal frequency is linear change in time, and its mathematic(al) representation is:

s(t)＝Acos[2πθ(t)]＝Acos[2πft] (1)

$\frac{\mathrm{d\θ}\left(t\right)}{\mathrm{dt}}={\mathrm{\θ}}^{\′}\left(t\right)=f_i\left(t\right)=F_B+\left(\frac{F_E-F_B}{T}\right)t---\left(2\right)$

F in the formula _BBe sweep signal initial frequency, F _EBe sweep signal end of a period frequency, T is duration scanning.

The first step, with command parameter F _B, F _E, parameter such as T passes to DSP from the ARM development board by the SCI interface, Fig. 2 is SCI interface circuit figure, it should be noted that the baud rate of ARM development board and dsp chip SCI interface must be identical, the order of parameter transmission and reception also must be identical.

Second step, calculate the output sample number according to the sweep time length and the sampling point time interval, sampling point is spaced apart the t microsecond, if time span is set to T, sampling point number N is so: N=1000000*T/t.DSP must execute the present embodiment content in the t microsecond time third and fourth step, (that dsp chip selects for use was float-point DSP processor TMS320F28335, can satisfy rate request), the output time of N sampling point is spaced apart the t microsecond simultaneously, time interval t can do certain modification as requested, but be subject to the speed of dsp processor, can not be less than 2 microseconds.Next DSP also will calculate the correction factor of each sampling point correspondence according to the windowing type that receives, and is generally the BlackMan window, so only need get final product in strict accordance with the coefficient value that computing formula is obtained N sampling point correspondence, coefficient value greater than 0 less than 1.

The 3rd step, at first according to initial frequency, finish frequency and scanning formula, obtain the corresponding relation of signal output frequency and time.

Can obtain by formula (2):

$\mathrm{\&theta;}\left(t\right)=\&Integral;f_i\left(t\right)\mathrm{dt}=F_{B}t+\frac{1}{2}\left(\frac{F_E-F_B}{T}\right){\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="HSA00000037171300012.png"\; state="\{\{state\}\}">t</figure-callout>}}^2+c---\left(3\right)$

Make c=0, can get:

$s\left(t\right)=A\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HSA00000037171300012.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&pi;}[F_B+\left(\frac{F_E-F_B}{2T}t\right)t]---\left(4\right)$

Obviously as can be known, f no longer is a fixing constant, but is shown below by following formula:

$f=F_B+\frac{F_E-F_B}{2T}t---\left(5\right)$

This formula is output signal t frequency constantly, and it increases in time and changes, and is the parameter of real-time change.

By the DDS theory as can be known, as signal frequency f and sample frequency f _cBetween when following the relation arranged:

$f/f_c=K/M<\frac{1}{2},$ Following formula is arranged:

$f=\frac{K{f}_c}{M}---\left(6\right)$

Formula (5) is carried out discretize (T _c=1/f _c), then can get by formula (6):

$F_B+\frac{F_E-F_B}{2T}n{T}_c=K{f}_c/M---\left(7\right)$

That is: $K=\frac{F_B+\frac{F_E-F_B}{2T}\mathrm{<figure-callout\; id="2"\; label="nM\; f\; c"\; filenames="HSA00000037171300012.png"\; state="\{\{state\}\}">nM</figure-callout>}}{f_c^{}}$

The K value is phase increment, can be obtained the sampling point amplitude of not windowing by K value and formula (6), formula (1).

The sampling point of the window function amplitude that computing obtained during the sampling point amplitude of the 4th step, not windowing that previous step is calculated went on foot with second carries out point-to-point multiplication, promptly obtains the amplitude after the windowing.This amplitude is a floating number, can not directly deliver to the DA converter as output, so the amplitude after the windowing also will be taken advantage of fixing coefficient, this coefficient is relevant with the figure place of used DA converter, adopts 16 in the native system, should multiply by 65535 so, and then round, deliver to the DA converter at last.

After the 5th step, dsp chip system deliver to the DA converter with the amplitude of calculating as a sampling point, carry out the DA conversion by DSP control DA chip, the conversion interface circuit between DSP and the DA chip as shown in Figure 4; Voltage after changing will pass through low-pass filter, as shown in Figure 3.Adopt SPI mouth and DSP to carry out communication, SPI is operated under the 50M speed, the SYNC frame synchronization pin of DA links to each other with the GPI060 pin of DSP, the transmission that comes the control data frame by setting and zero clearing to the GPI060 pin, the side of fortune U1 is used for improving output impedance, among Fig. 3 filtering is carried out in DA output, filter capacitor size be 10PF, and is definite according to exporting the end of a period frequency signal.Reference voltage VREF421 can revise filtered voltage drift, further improves the output amplitude precision, and reference voltage is chip used to be ADR421.The simulating signal of coming out from wave filter is as final output signal.

The 6th step, the total sampling point output number N that determines according to the first step and sampling point output time t at interval decide the number and the frequency of continuous output sample, decide the wheel number of times of the continuous wave of exporting according to the cascade scanning number of times, decide the start and stop of output according to start stop command.

Claims (3)

1. the production method of the special-purpose swept-frequency signal of a vibroseis is characterized in that:

(1), presets the program that in the system that constitutes by dsp chip, deposits various waveforms in by software;

(2), by ARM development board input command parameter in the dsp chip system, comprise signal type, initial frequency, end frequency, sweep time length, cascade scanning number of times, whether windowing, window function type, start, stop;

(3), DSP finishes the computing of output sample phase increment according to the parameter that is provided with and generates and the corresponding amplitude of wave function, and then amplitude is carried out windowing process;

(4), the DA converter then is converted to operation result the output of analog quantity, obtains final output simulating signal through a low-pass filter at last.

2. the production method of the special-purpose swept-frequency signal of a kind of vibroseis according to claim 1 is characterized in that passing to the dsp chip system by the command parameter of ARM development board input by the SCI interface.

3. the production method of the special-purpose swept-frequency signal of a kind of vibroseis according to claim 2 is characterized in that the dsp chip system carries out the DA conversion by DSP and DA switching device interface control DA chip.

Images