CN105024654B - Frequency-selecting amplifying circuit for pseudo-random signal by electrical method - Google Patents
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Abstract
A frequency-selective amplifying circuit of a pseudorandom signal electrical method comprises a crystal oscillator (1), a programmable logic device (2), a resistor (3), a resistor (4), an operational amplifier (5), a resistor (6), a capacitor (7), a first single-pole double-throw analog switch (8) and a second single-pole double-throw analog switch (9), wherein the programmable logic device (2) is provided with a non-inverting output end (10) and an inverting output end (11), and the signal-to-noise ratio can be improved as much as possible through frequency-selective amplification. The method is beneficial to improving the detection precision and the exploration accuracy of the electrical method signals of the pseudo-random signals, can measure the signals in a measuring area farther away from the emission source, thus increasing the receiving and transmitting distances of the electrical method measurement of the pseudo-random signals and expanding the exploration range.
Description
Technical Field
The invention relates to the technical field of signal amplification in an exploration type detecting instrument, in particular to a frequency-selecting amplifying circuit of a pseudorandom signal electrical method in an electrical method detecting instrument.
Background
In the field of frequency domain electromagnetic prospecting, the amplitude and the phase of a specific frequency signal need to be measured, signals with different frequencies correspond to underground information with different prospecting depths, and dozens of frequencies need to be measured in order to acquire the underground information with different depths. In general, survey devices perform measurements in a frequency sweep fashion, with the transmitter transmitting a square wave signal at one frequency at a time, and the receiver measuring the signal produced by exciting the subsurface medium at that transmitted frequency until all frequencies have been measured. The measuring mode is low in field efficiency, and construction cost is increased. For example, chinese patent application publication nos. CN1683941A and CN103969688A in the prior art respectively disclose a pseudo-random three-frequency ground-electrical response measurement method and a pseudo-random signal electrical prospecting method, both of which improve observation efficiency by emitting a pseudo-random signal containing a plurality of useful signal frequencies, and can complete measurement of a plurality of frequencies by one-time emission.
For the electrical method of pseudo-random signals, under the condition of a certain total transmitting power, the transmitting power of each frequency is reduced due to the transmission of multi-frequency pseudo-random signals, and the strength of signals measured by a receiver is reduced, so that an amplifying circuit with the function of improving the signal-to-noise ratio is particularly important. Therefore, the signal amplifying circuit is an important component of the electrical detection instrument for the pseudo-random signal. However, in the field exploration process, the signals measured by the receiver are very weak, and are also affected by various electromagnetic noises, such as earth electric noise, power frequency and harmonic noise thereof, radio communication noise, etc., which have wide spectrum distribution and overlap with the frequency range of the measured signals, and in order to accurately measure the signals, the frequency-selective amplification of the transmitted frequency signals is required, that is, the selective amplification of specific frequencies is performed without amplifying the noise.
The applicant has searched and found some related prior arts, such as:
the Chinese patent application with publication number CN1683941A discloses a pseudo-random tri-band geoelectric response measuring device for a ground electric field, wherein the dual-channel ground electric field signal acquisition receiver comprises at least two tri-band signal extraction channels with completely the same parameters and a single chip microcomputer system, each signal extraction channel comprises an electric field sensor, a common channel, a low-frequency channel, an intermediate-frequency channel, a high-frequency channel, an A/D conversion circuit and a timing and logic control circuit, the output end of the electric field sensor of the tri-band signal extraction channel is connected to the input end of a high-pass filter circuit, the output end of the high-pass filter circuit is connected to the input end of a preamplifier, the output end of the preamplifier is connected to the input end of a low-pass filter circuit, the input end of a middle-stage amplifier circuit is connected to the output end of the low-pass filter circuit, the output, The input ends of the intermediate frequency band-pass filter circuit and the high frequency band-pass filter circuit; the output end of the low-frequency band-pass filter circuit is connected to the input end of the low-frequency amplifier, the output end of the low-frequency amplifier is connected to the input end of the low-frequency detection and integration circuit, and the output end of the low-frequency detection and integration circuit is connected to the input end of the integral A/D conversion circuit; the output end of the intermediate frequency band-pass filter circuit is connected to the input end of the intermediate frequency amplifier, the output end of the intermediate frequency amplifier is connected to the input end of the intermediate frequency detection and integration circuit, the output end of the intermediate frequency detection and integration circuit is connected to the input end of the integral A/D conversion circuit, the output end of the high frequency band-pass filter circuit is connected to the input end of the high frequency amplifier, the output end of the high frequency amplifier is connected to the input end of the high frequency detection and integration circuit, and the input end of the high frequency detection and integration circuit is connected to the; the output end of the integral A/D conversion circuit is connected to the input end of the singlechip system, and the singlechip system is connected to the timing and control logic circuit through an I/O interface line. The invention firstly utilizes the common channel to process the broadband signal, uses the preamplifier and the intermediate-stage amplifier to amplify all frequencies, and then respectively uses the low-frequency channel, the intermediate-frequency channel and the high-frequency channel to carry out band-pass filtering and amplification on the three frequencies, the circuit structure is complex, the cost is high, the power consumption, the volume and the instability factors of the instrument are increased, and the device can only receive the signals of the three frequencies, thereby reducing the information quantity obtained by exploration and limiting the application range of the instrument.
Chinese patent application publication No. CN103969688A discloses a method and apparatus for electrical prospecting of pseudo-random signals, which can obtain frequency response in a wide frequency band, and a pseudo-random signal receiving and processing module performs a/D conversion on the received signals to convert them into digital signals. The transmission signal adopted by the invention is an m sequence, the m sequence contains more frequency components, the transmission power of each frequency component is very low, and the measurement signal is very weak.
The Chinese patent application with the publication number of CN201705340U discloses a controllable signal receiver capable of loading pseudo-random codes, which is used for detecting and receiving electric signals in the process of oil field exploration and development and at least comprises a signal acquisition and amplification unit, a filtering unit and an A/D conversion unit which are sequentially connected, wherein the signal acquisition and amplification unit amplifies acquired field signals and then transmits the amplified signals to the filtering unit and the A/D conversion unit for processing. The adopted amplification mode is broadband amplification, noise is amplified while signals are amplified, the signal-to-noise ratio is not improved, and the quality of measured data is poor.
The existing pseudo-random signal electrical method instrument also has the following problems: the used amplifier can not carry out frequency-selective amplification aiming at the signal spectrum characteristics, or a plurality of channels are needed to amplify specific frequencies, and when broadband amplification is used, the signal-to-noise ratio is not improved; when a plurality of channels are used, the system structure is large, the cost is increased, and the frequency that can be selected for amplification is limited.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a frequency selection amplifying circuit for a pseudo-random multi-frequency signal.
The purpose of the invention is realized by the following modes:
the frequency-selecting amplifier circuit of pseudo-random signal electric method is characterized in that a crystal oscillator is connected with a clock input end of a programmable logic device, a non-inverting output end of the programmable logic device is connected with a control end of a single-pole double-throw analog switch, an inverting output end of the programmable logic device is connected with the control end of the single-pole double-throw analog switch, an input signal is connected with an inverting input end of an operational amplifier through a resistor, a non-inverting input end of the operational amplifier is connected with a reference ground through the resistor, an inverting proportional input end of the operational amplifier is connected with a moving end of the single-pole double-throw analog switch, a fixed end A of the single-pole double-throw analog switch is connected with one input end of the resistor, a fixed end A of the single-pole double-throw analog switch is connected with one input end of a capacitor, a fixed end A of the single-pole double-throw analog switch is connected, one fixed end B of the single-pole double-throw analog switch is connected to the other input end of the resistor, one fixed end B of the single-pole double-throw analog switch is connected to the other input end of the capacitor, one fixed end B of the single-pole double-throw analog switch is connected to one fixed end D of the single-pole double-throw analog switch, and the movable end of the single-pole double-throw analog switch is connected to the output end of the operational amplifier.
The invention has the following beneficial effects:
(1) the frequency-selecting amplifying circuit in the pseudorandom signal electrical method instrument provided by the invention amplifies signals with useful frequencies on the premise of not amplifying noise (the useful frequencies refer to frequency components with higher energy in a pseudorandom signal waveform transmitted by a transmitter, different useful frequencies are used for acquiring apparent resistivity information at different depths, the useful frequencies are removed, and signals with other frequencies are regarded as noise), so that the signal-to-noise ratio can be improved as much as possible through frequency-selecting amplification. In a comparative experiment in which the same input signal was measured in the field, the signal-to-noise ratio using the frequency selective amplifier circuit of the present invention was 26dB, whereas the signal-to-noise ratio using the broadband amplifier circuit in the same type of exploration equipment was only-198 dB.
(2) The signal-to-noise ratio is improved, so that the detection precision and the exploration accuracy of the electrical method signals of the pseudo-random signals are improved, the signals can be measured in a measuring area farther away from the emission source, the receiving and transmitting distances of the electrical method measurement of the pseudo-random signals are increased, and the exploration range is expanded. Other receivers using pseudo-random signals may use the present amplification circuit to improve signal-to-noise ratio.
Drawings
FIG. 1 is a schematic block diagram of a frequency-selecting amplifying circuit in a pseudo-random signal electrical method instrument.
FIG. 2 is 2nA sequence three-frequency pseudo-random signal waveform diagram.
FIG. 3 is a view of use 2nThe transmission characteristic curve graph of the frequency selection amplifying circuit when the pseudo-random signal is a sequence three-frequency pseudo-random signal.
The reference numerals in fig. 1 have the following meanings: 1-crystal oscillator, 2-programmable logic device, 3-resistor, 4-resistor, 5-operational amplifier, 6-resistor, 7-capacitor, 8-single-pole double-throw analog switch, 9-single-pole double-throw analog switch, 10-non-inverting output terminal of programmable logic device 2, and 11-inverting output terminal of programmable logic device 2.
Detailed Description
The circuit and embodiments of the invention are described in further detail below with reference to the accompanying drawings:
fig. 1 is a schematic block diagram of a frequency-selecting amplifier circuit in a pseudo-random signal electrical instrument, an input signal s (t) is first connected to an inverting input terminal of an operational amplifier 5 through a first resistor 3, and a current input to the inverting input terminal of the operational amplifier 5 is represented as:
in the above formula RiIs the resistance value of the first resistor 3 in the frequency-selective amplifying circuit.
The non-inverting input terminal of the operational amplifier 5 is connected to the reference ground through the second resistor 4, and the second resistor 4 is used for balancing the impedance of the two input terminals of the operational amplifier and eliminating the input bias voltage. The inverting input terminal voltage of the operational amplifier 5 is also 0 according to the "virtual short" characteristic of the operational amplifier. The inverting input terminal of the operational amplifier 5 is connected to the moving terminal of the single-pole double-throw analog switch 8, and the model of the operational amplifier can be selected from OP07 and the like.
The crystal oscillator 1 is a quartz clock with an output frequency of 20 MHz. The crystal oscillator 1 provides a running clock with stable frequency for the programmable logic device 2, and the programmable logic device 2 adopts the EPM 240. The method comprises the steps that a pseudo-random signal sequence is generated inside a programmable logic device, and because the pseudo-random signal sequence is a periodic signal and meets the Dirichlet condition, a pseudo-random signal p (t) is expanded into a form of an exponential Fourier series:
in the above formula, T represents time, T0 represents integration start time, T represents a period of the pseudorandom signal, n is an integer from negative infinity to positive infinity, P (n ω 0) represents a frequency spectrum of the pseudorandom signal P (T), ω 0 represents a frequency resolution of performing the frequency spectrum analysis, and the frequency resolution of the frequency spectrum analysis can be obtained by dividing a sampling rate by the number of sampling points. The generated pseudo-random signal is divided into two paths of in-phase and anti-phase output. The in-phase pseudo-random signal p (t) sequence is directly connected to the control end of the single-pole double-throw analog switch 8, the other path of the in-phase pseudo-random signal is changed into an inverted pseudo-random signal sequence through an inverter, the inverted pseudo-random signal is connected to the control end of the single-pole double-throw analog switch 9, and the single-pole double-throw analog switch can be selected from ADG 1436. The third resistor 6 and the capacitor 7 form an RC parallel network, the immobile end A of the single-pole double-throw analog switch 8 is connected to one end of the RC parallel network, one end of the RC parallel network is also connected with the immobile end C of the single-pole double-throw analog switch 9, the immobile end B of the single-pole double-throw analog switch 8 is connected to the other end of the RC parallel network, the other end of the RC parallel network is also connected with the immobile end D of the single-pole double-throw analog switch 9, and the mobile end of the single-pole double-throw analog switch 9 is connected with the output end of the operational amplifier 5.
When the frequency-selecting amplifying circuit in the pseudorandom signal electrical method instrument works, the levels of the in-phase output end and the reverse phase output end of the programmable logic device 2 are opposite, namely when the output of the in-phase output end is '1', the output of the reverse phase output end is '0', and vice versa. When the output of the in-phase output end is '1' and the output of the anti-phase output end is '0', the moving end of the single-pole double-throw analog switch 8 is switched on A, and the moving end of the single-pole double-throw analog switch 9 is switched on D, so that the current flowing from the input signal through the first resistor 3 flows through the RC parallel network from top to bottom; when the output of the in-phase output terminal is '0' and the output of the anti-phase output terminal is '1', the moving terminal of the single-pole double-throw analog switch 8 is turned on B, and the moving terminal of the single-pole double-throw analog switch 9 is turned on C, so that the current flowing from the input signal through the first resistor 3 flows through the RC parallel network from bottom to top. Therefore, the input current is controlled by the two single-pole double-throw analog switches to change the direction according to a pseudo-random signal sequence, the RC parallel network is alternately charged, namely the input current is multiplied by a pseudo-random signal, and then the equivalent current x (t) flowing through the RC parallel network is expressed as:
in the above formula, s (t) represents an input signal, RiIs the resistance value of the first resistor 3 in the frequency-selective amplifying circuit.
The input signal s (t) is multiplied and then Fourier transformed, and the frequency shift characteristic of Fourier transform is used to obtain
F[s(t)exp(jω0t)]＝S(ω-ω0)
In the above equation, F denotes a fourier operator, and S (ω - ω 0) denotes a frequency spectrum S (ω) of the input signal S (t) shifted by ω 0.
The frequency spectrum X (ω) of the equivalent current X (t) flowing through the RC parallel network can be expressed as:
according to the property of fourier transform, for a signal S (t) with real voltage, the real part of the frequency spectrum S (ω) is an even signal, the imaginary part is an odd signal, and the frequency spectrum of the equivalent current flowing through the RC parallel network is represented as:
with the resistance of the third resistor 6 being Rf and the capacitance of the capacitor 7 being C, the impedance of the parallel network can be expressed as:
the frequency spectrum U (ω) of the output voltage of the operational amplifier 5, obtained by multiplying the current flowing through the RC parallel network by the impedance of the parallel network, is:
in the above formula, "+" represents convolution operation, the output of the operational amplifier 5 is the output of the amplifying circuit, and the transmission characteristic function of the frequency-selecting amplifying circuit of the finally obtained pseudo-random signal is:
the method represents an impulse function, and the amplitude-frequency transmission characteristic function of the frequency-selective amplifying circuit of the pseudo-random signal is as follows:
it can be seen that when the frequency of the input signal is n ω 0, it can be obtained
When the frequency of the input signal is far away from the frequency n omega 0 of the pseudo-random signal, the amplitude-frequency response of the frequency-selective amplifying circuit is as follows:
as the frequency of the input signal moves away from n ω 0, the circuit output amplitude decreases as ω -n ω 0 increases. As can also be seen from the above formula, RfThe larger C, the narrower the frequency band of the frequency selective amplifier, and the larger RfOr C can make the amplification bandwidth smaller and reduce the influence of noise to the maximum extent.
In summary, the frequency selective amplifier circuit performs frequency selective amplification on the input signal according to the frequency spectrum distribution of the pseudorandom signal, and therefore, the frequency selective amplifier circuit is very suitable for amplifying a specific frequency signal in the electrical method of the pseudorandom signal. Through field comparison experiments, the signal-to-noise ratio of the frequency-selecting amplifying circuit is 26dB, and the signal-to-noise ratio of the broadband amplifying circuit in the same exploration equipment is only-198 dB.
Examples
The following description will be given by taking a 2n pseudo-random sequence signal used in the pseudo-random signal electrical method as an example. When the electrical prospecting of the pseudorandom signal is carried out, a transmitter transmits a 2n three-frequency pseudorandom sequence by using a long wire with two grounded ends, wherein the long wire is generally 1-3 kilometers. Electromagnetic waves generated by the transmitted pseudo-random signals are transmitted to the underground, underground target bodies are stimulated to generate induction signals, and the receiver measures the electromagnetic induction signals. The pseudo-random three-frequency electrical response measuring method is disclosed by the patent CN1683941A, and is not described in detail herein. The following mathematical expression of the current waveform can be used as the measurement signal:
the above formula 2nThe three-frequency pseudo-random sequence waveform is shown in figure 2, and the frequency spectrum of the three-frequency pseudo-random sequence waveform comprises three main frequencies f0，2f0，4f0，f0Is 2nThe fundamental frequency of the three-frequency pseudo-random sequence, the corresponding amplitudes of which are 0.9003A, 0.6366A, 0.6366A and 2n respectively, also comprises 3f0，5f0，6f0，7f0，9f0But are not considered useful frequencies in electrical prospecting for pseudo-random signals because these frequencies have less energy than the three primary frequencies. Thus, a 2n three-frequency pseudorandom sequence spectrum can be approximated as:
P(nω0)≈0.9003(f0)+0.6366(2f0)+0.6366(4f0)
the receiver receives the induction signal through the electric field or magnetic field sensor and then sends the induction signal to the receiving detection circuit, and firstly, the frequency-selecting amplification circuit shown in fig. 1 is needed for amplification. The resistance Ri of the first resistor 3 is set to 100 Ω, and the current flowing into the operational amplifier 5 after passing through the first resistor 3 is:
the programmable logic device 2 outputs a 2n three-frequency pseudo-random sequence with one path of same phase and one path of opposite phase to respectively control the single-pole double-throw analog switch 8 and the single-pole double-throw analog switch 9, wherein the sequence for controlling the single-pole double-throw analog switch 9 is an opposite-phase signal for controlling the sequence of the single-pole double-throw analog switch 8, and simultaneously, according to the 'virtual break' characteristic of the operational amplifier, the current flowing from the first resistor 3 flows through the RC parallel network. The equivalent current x (t) flowing through the RC parallel network is represented as:
the spectrum of the current flowing through the RC parallel network is:
when the resistance of the third resistor 6 is Rf, the capacitance of the capacitor 7 is C, Rf is 100k Ω, and C is 100 μ F, the impedance of the parallel network can be expressed as:
the frequency spectrum U (ω) of the output voltage of the operational amplifier 5 obtained by multiplying the current flowing through the RC parallel network by the resistance of the RC parallel network is:
in the above formula, "+" represents convolution operation, the output of the operational amplifier 5 is the output of the amplifying circuit, and the transmission characteristic function of the frequency-selecting amplifying circuit of the finally obtained pseudo-random signal is:
the transmission characteristic curve diagram of the 2n sequence three-frequency pseudo-random signal frequency selection amplifying circuit is shown in figure 3 when f0 is 100 Hz. As can be seen from the figure, the frequency selective amplifier can be pairedThe three main frequencies 100Hz, 200Hz and 400Hz are amplified by 900.3 times, 636.6 times and 636.6 times, respectively, other frequencies that can be amplified include 300Hz, 500Hz, 600Hz, 700Hz and 900Hz, corresponding to 300, 180, 212, 129 and 100 times, although 2 Hz is transmitted at the transmitternA tri-band pseudo-random sequence contains these spectral components but is not used because of its lower energy than the three main frequency spectra. While the gain for other frequencies is about 0.3. Thus, by being in 2nThe frequency-selecting amplifying circuit is used in a three-frequency pseudo-random signal electrical method detecting instrument, the useful three main frequencies of 100Hz, 200Hz and 400Hz are amplified by more than 600 times, the signal frequency transmitted by a transmitter contains 300Hz, 500Hz, 600Hz, 700Hz and 900Hz which are not used in exploration, the amplification factor is more than 100, and the gain of other frequencies containing noise is 0.3, namely the attenuation is about one third of the original gain.
This example, through a description and calculation of a specific exemplary application, advantageously demonstrates that the frequency selective amplifier circuit of the present invention amplifies useful frequencies in electrical prospecting of pseudorandom signals, attenuates noise at other frequencies, and by comparison experiments in which the same input signal is measured in the field, the signal-to-noise ratio using the frequency selective amplifier circuit of the present invention is 26 dB; the signal-to-noise ratio of the broadband amplifying circuit in the same exploration equipment is only-198 dB, and the signal-to-noise ratio is greatly improved. The signal-to-noise ratio is improved, so that the detection precision and the exploration accuracy of the electrical method signals of the pseudo-random signals are improved, the signals can be measured in a measuring area farther away from the emission source, the receiving and transmitting distances of the electrical method measurement of the pseudo-random signals are increased, and the exploration range is expanded.
Claims (1)
1. A frequency-selective amplifying circuit of a pseudo-random signal electric method is characterized by comprising a crystal oscillator (1), a programmable logic device (2), a first resistor (3), a second resistor (4), an operational amplifier (5), a third resistor (6), a capacitor (7), a first single-pole double-throw analog switch (8) and a second single-pole double-throw analog switch (9), wherein the programmable logic device (2) is provided with a non-inverting output end (10) and an inverting output end (11); the crystal oscillator (1) is connected with a clock input end of a programmable logic device (2), a non-inverting output end (10) of the programmable logic device (2) is connected with a control end of a first single-pole double-throw analog switch (8), an inverting output end (11) of the programmable logic device (2) is connected with a control end of a second single-pole double-throw analog switch (9), an input signal is connected with an inverting input end of an operational amplifier (5) through a first resistor (3), a non-inverting input end of the operational amplifier (5) is connected with a reference ground through a second resistor (4), an inverting proportional input end of the operational amplifier (5) is connected with a movable end of the first single-pole double-throw analog switch (8), a non-movable end A of the first single-pole double-throw analog switch (8) is respectively connected with an input end of a third resistor (6), an input end of a capacitor (7) and a non-movable end C of the second single-pole double-throw analog switch (9), the other fixed end B of the first single-pole double-throw analog switch (8) is respectively connected to the other input end of the third resistor (6), the other input end of the capacitor (7) and the other fixed end D of the second single-pole double-throw analog switch (9), and the movable end of the second single-pole double-throw analog switch (9) is connected to the output end of the operational amplifier (5).
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