CN108847827B - Continuous variable gain amplifying circuit applied to ultrasonic gas meter - Google Patents
Continuous variable gain amplifying circuit applied to ultrasonic gas meter Download PDFInfo
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- CN108847827B CN108847827B CN201811021411.3A CN201811021411A CN108847827B CN 108847827 B CN108847827 B CN 108847827B CN 201811021411 A CN201811021411 A CN 201811021411A CN 108847827 B CN108847827 B CN 108847827B
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- 238000001514 detection method Methods 0.000 description 8
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Classifications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/68—Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics
Abstract
The invention discloses a continuous variable gain amplifying circuit applied to an ultrasonic gas meter, which comprises a receiving-transmitting switching and exciting integrated circuit, an echo analog amplifying circuit and a high-frequency peak signal holding circuit, wherein the receiving-transmitting switching and exciting integrated circuit comprises a first transducer, a second transducer and a switch group, an ultrasonic signal received by the first transducer or the second transducer is obtained by the switch group and is transmitted to the echo analog amplifying circuit, the echo analog amplifying circuit comprises an operational amplifier group formed by a plurality of operational amplifiers, the differential signal outputs the ultrasonic signal through the echo analog amplifying circuit and is transmitted to the high-frequency peak signal holding circuit, the high-frequency peak signal holding circuit comprises a power detector and a seventh operational amplifier, the ultrasonic signal is shaped into a low-frequency envelope signal through the power detector, and the low-frequency envelope signal is held by the seventh operational amplifier for sampling. The influence of the change in the properties of the gaseous medium on the amplitude of the received echo is reduced.
Description
Technical Field
The invention relates to a detection circuit in an ultrasonic gas meter, in particular to a continuous variable gain amplification circuit applied to the ultrasonic gas meter, which is a front-end circuit design for ultrasonic flow detection.
Background
Ultrasonic flow detection mode has been widely used at present, but no mature ultrasonic gas meter is proposed at present. The difficulty is mainly that the propagation medium of ultrasonic waves in the meter is gas, the volume and the density of the ultrasonic waves can be changed at different temperatures and pressures, and the gas components in various places in China are different.
According to the ultrasonic gas meter verification procedure, the gas medium used for verification is air. The same transducer at normal temperature and normal pressure has larger difference on the received echo under the excitation of fixed voltage, which is influenced by the property change of the gas medium. Mainly represented by changes in the time of flight caused by changes in the propagation speed of the ultrasonic wave and changes in the amplitude of the echo caused by changes in the decay rate during the propagation of the acoustic wave.
This requires that the ultrasonic gas meter can accurately meter in different gaseous media (such as air, natural gas, etc.) under different working conditions (such as varying temperature, pressure, etc.). Therefore, the present inventors have devised to achieve this objective by employing a continuously variable gain analog front end in an ultrasonic gas meter to minimize the effect of changes in the properties of the gaseous medium on the amplitude of the received echoes. A signal processing circuit based on a continuously variable gain amplification circuit is proposed. And by combining the function of the head wave detection mode of the TDC-GP22 flight time measuring chip of the German ACAM company, the closed-loop control of the amplitude of the echo signal of the ultrasonic transducer is realized by externally adding an echo amplitude measuring circuit, and the problem of false triggering of a rear-end comparator signal caused by indistinguishable head wave and noise under the condition that the echo of the signal of the ultrasonic transducer is weak is effectively solved.
Disclosure of Invention
The invention aims to solve the technical problem of providing a continuous variable gain amplifying circuit applied to an ultrasonic gas meter, which can furthest reduce the influence of the property change of a gas medium on the amplitude of a received echo and provide AD sampling signals for a subsequent TDC-GP22 flight time measuring chip.
The technical scheme adopted for solving the technical problems is as follows: the continuous variable gain amplifying circuit comprises a receiving-transmitting switching-exciting integrated circuit, an echo analog amplifying circuit and a high-frequency peak signal holding circuit, wherein the receiving-transmitting switching-exciting integrated circuit comprises a first transducer, a second transducer and a switch group, an ultrasonic signal received by the first transducer or the second transducer is obtained by the switch group and is transmitted to the echo analog amplifying circuit, the echo analog amplifying circuit comprises an operational amplifier group formed by a plurality of operational amplifiers, the differential signal outputs the ultrasonic signal through the echo analog amplifying circuit and is transmitted to the high-frequency peak signal holding circuit, the high-frequency peak signal holding circuit comprises a power detector with the model of LTC5507 and a seventh operational amplifier, the ultrasonic signal is shaped into a low-frequency envelope signal through the power detector, and the low-frequency envelope signal is held for sampling through the seventh operational amplifier.
The invention further preferably comprises the following steps: the switch group all adopts the duplex switch, and the switch group includes first switch, second switch, fifth switch, sixth switch, seventh switch and eighth switch, the both ends of first transducer connect the public end of first switch, the public end of second switch respectively, the fulcrum one of first switch connect to the fulcrum one of fifth switch, the public end of fifth switch output P way signal, fulcrum two of first switch pass through seventh switch optional connection power or ground wire, fulcrum one of second switch connect to the fulcrum one of sixth switch, the public end output N way signal of sixth switch, fulcrum two of second switch pass through eighth switch optional connection power or ground wire, P way signal constitute differential signal transmission for echo analog amplifier circuit with N way signal.
The invention further preferably comprises the following steps: the switch group also comprises a third switch, a fourth switch, a ninth switch and a tenth switch, wherein two ends of the second transducer are respectively connected with a common end of the third switch and a common end of the fourth switch, a second fulcrum of the third switch is connected to a second fulcrum of the fifth switch, the first fulcrum of the third switch is selectively connected with a power supply or a ground wire through the ninth switch, the second fulcrum of the fourth switch is connected with a second fulcrum of the sixth switch, and the first fulcrum of the fourth switch is selectively connected with the power supply or the ground wire through the tenth switch.
The invention further preferably comprises the following steps: the operational amplifier group comprises a first operational amplifier, a third operational amplifier and a fifth operational amplifier, P paths of signals are input to the reverse input end of the first operational amplifier, the output end of the first operational amplifier is connected with the in-phase input end of the third operational amplifier, a first resistor and a first capacitor which are connected in parallel are arranged between the reverse input end and the output end of the first operational amplifier, the output end of the third operational amplifier is connected to the reverse input end of the fifth operational amplifier, a digital resistor is connected between the reverse input end and the output end of the third operational amplifier, and the output end of the fifth operational amplifier outputs ultrasonic signals.
The invention further preferably comprises the following steps: the operational amplifier group also comprises a second operational amplifier and a fourth operational amplifier, N paths of signals are input to the reverse input end of the second operational amplifier, the output end of the second operational amplifier is connected with the in-phase input end of the fourth operational amplifier, a second resistor and a second capacitor which are connected in parallel are arranged between the reverse input end and the output end of the second operational amplifier, the output end of the fourth operational amplifier is connected to the in-phase input end of the fifth operational amplifier, a digital resistor is connected between the reverse input end and the output end of the fourth operational amplifier, the in-phase input end of the fifth operational amplifier is connected with a 1.5V voltage source through a tenth resistor, and the in-phase input end of the first operational amplifier and the in-phase input end of the second operational amplifier are connected between the tenth resistor and the 1.5V voltage source through wires.
The invention further preferably comprises the following steps: the ultrasonic signal is connected to a third pin of the power detector through a sixth capacitor, the sixth pin of the power detector is connected to a non-inverting input end of a seventh operational amplifier, an output end of the seventh operational amplifier is connected to an anode end of the first diode, a cathode end of the first diode is grounded after passing through the seventh capacitor, and an inverting input end of the seventh transport amplifier is connected to a cathode end of the first diode.
Compared with the prior art, the invention has the advantages that the measurement principle of the time difference method is used, and the fluid flow is measured by utilizing the reciprocal difference of forward flow propagation time and backward flow propagation time of sound waves in flowing gas in proportion to the fluid flow velocity. The invention designs a front-end processing circuit for the signals to be collected by the TDC-GP22 chip, and mainly realizes the functions of excitation of ultrasonic signals, continuous program-controlled amplification and amplitude detection of echo signals, flight time detection of the ultrasonic signals, receiving and transmitting switching of an ultrasonic transducer and the like. According to the measuring principle of the time difference method, the first transducer and the second transducer are set to be mutually switched between transmitting and receiving states, and the measurement of forward and reverse flight time is completed. In order to prevent false triggering of the comparator inside the back-end TDC-GP22 chip, the signal to noise ratio is improved by improving the excitation voltage of the transducer or increasing the amplification factor of the back-end operational amplifier. But increasing the excitation voltage can further increase the emission power of the ultrasonic transducer and increase the system power consumption, so the design mainly adopts differential excitation to improve the excitation efficiency, the circuit structure is greatly simplified compared with a high-voltage excitation circuit needing inductance, the working current is close to low-voltage single-ended excitation, and the design is completely realized by adopting a low-voltage analog switch of the same type. The differential signal outputs an ultrasonic signal through the echo analog amplifying circuit and transmits the ultrasonic signal to the high-frequency peak signal holding circuit, the ultrasonic signal is shaped into a low-frequency envelope signal through the power detector, and the low-frequency envelope signal is sampled through the seventh operational amplifier.
Drawings
FIG. 1 is a diagram of a transmit-receive switching and excitation integrated circuit;
FIG. 2 is an echo analog amplification circuit;
fig. 3 is a high frequency peak signal holding circuit.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
As shown in fig. 1 to 3: the continuous variable gain amplifying circuit comprises a receiving-transmitting switching-exciting integrated circuit, an echo analog amplifying circuit and a high-frequency peak signal holding circuit, wherein the receiving-transmitting switching-exciting integrated circuit comprises a first transducer Y1, a second transducer Y2 and a switch group, an initial signal received by the first transducer Y1 or the second transducer Y2 is obtained by the switch group and is transmitted to the echo analog amplifying circuit, the echo analog amplifying circuit comprises an operational amplifier group formed by a plurality of operational amplifiers, the differential signal outputs an ultrasonic signal Ultrasonicwave through the echo analog amplifying circuit and is transmitted to the high-frequency peak signal holding circuit, the high-frequency peak signal holding circuit comprises a power detector U6 and a seventh operational amplifier U7, the model number of the ultrasonic signal Ultrascwave is shaped into a low-frequency envelope signal through the power detector U6, and the low-frequency envelope signal is held by the seventh operational amplifier U7 for sampling. The first transducer Y1 and the second transducer Y2 of the invention are all transmitting-receiving integrated gas ultrasonic transducers with the resonance frequency of 500 KHz.
The switch group comprises a first switch S1, a second switch S2, a fifth switch S5, a sixth switch S6, a seventh switch S7 and an eighth switch S8, wherein two ends of the first transducer Y1 are respectively connected with a public end of the first switch S1 and a public end of the second switch S2, a fulcrum one of the first switch S1 is connected with a fulcrum one of the fifth switch S5, a public end of the fifth switch S5 outputs a P-way signal Transducer P, a fulcrum two of the first switch S1 can be selectively connected with a power supply VCC or a ground wire through the seventh switch S7, a fulcrum one of the second switch S2 is connected with a fulcrum one of the sixth switch S6, a fulcrum two of the second switch S2 can be selectively connected with the power supply VCC or the ground wire through the eighth switch S8, and the P-way signal Transducer P and the N-way signal Transducer N form a differential signal echo analog amplification circuit.
The switch group further comprises a third switch S3, a fourth switch S4, a ninth switch S9 and a tenth switch S10, two ends of the second transducer Y2 are respectively connected with a common end of the third switch S3 and a common end of the fourth switch S4, a second fulcrum of the third switch S3 is connected to a second fulcrum of the fifth switch S5, a first fulcrum of the third switch S3 is selectively connected with a power source VCC or a ground wire through the ninth switch S9, a second fulcrum of the fourth switch S4 is connected with a second fulcrum of the sixth switch S6, and a first fulcrum of the fourth switch S4 is selectively connected with the power source VCC or the ground wire through the tenth switch S10.
The operational amplifier group comprises a first operational amplifier U1, a third operational amplifier U3 and a fifth operational amplifier U5, P paths of signal Transducer P are input to the reverse input end of the first operational amplifier U1, the output end of the first operational amplifier U1 is connected with the in-phase input end of the third operational amplifier U3, a first resistor R1 and a first capacitor C1 which are connected in parallel are arranged between the reverse input end and the output end of the first operational amplifier U1, the output end of the third operational amplifier U3 is connected to the reverse input end of the fifth operational amplifier U5, a digital resistor U6 is connected between the reverse input end and the output end of the third operational amplifier U3, and the output end of the fifth operational amplifier U5 outputs an ultrasonic signal Ultrasonic wave.
The operational amplifier group further comprises a second operational amplifier U2 and a fourth operational amplifier U4, N paths of signals TransducerN are input to the reverse input end of the second operational amplifier U2, the output end of the second operational amplifier U2 is connected with the in-phase input end of the fourth operational amplifier U4, a second resistor R2 and a second capacitor C2 which are connected in parallel are arranged between the reverse input end and the output end of the second operational amplifier U2, the output end of the fourth operational amplifier U4 is connected to the in-phase input end of the fifth operational amplifier U5, a digital resistor U6 is connected between the reverse input end and the output end of the fourth operational amplifier U4, the in-phase input end of the fifth operational amplifier U5 is connected with a 1.5V voltage source through a tenth resistor R10, and the in-phase input end of the first operational amplifier U1 and the in-phase input end of the second operational amplifier U2 are connected between the tenth resistor R10 and the 1.5V voltage source through wires.
The ultrasonic signal UltrasonicWave is connected to a third pin of the power detector U6 through a sixth capacitor C6, the sixth pin of the power detector U6 is connected to a non-inverting input end of a seventh operational amplifier U7, an output end of the seventh operational amplifier U7 is connected to an anode end of the first diode D1, a cathode end of the first diode D1 is grounded after passing through the seventh capacitor C7, and an inverting input end of the seventh conveying amplifier U7 is connected to a cathode end of the first diode D1.
The invention will now be further described with reference to the accompanying drawings: the first transducer Y1 and the second transducer Y2 are 500KHz transducer pairs used for measurement, and the switch groups S1-10 adopt SN74LVC1G3157DCKR analog switches. The S1-6 is controlled by a direction control signal output by an EN_START pin of the TDC-GP22, the corresponding bit of the SEL_TSTO2 in a No. 1 register of the TDC-GP22 chip is required to be modified to be 5, at the moment, the pin output low level '0' measures reverse flight time, the switch state is consistent with that shown in FIG. 1, the first transducer Y1 is in a receiving state, the second transducer Y2 is in a transmitting state, S7-10 are respectively controlled by a FIRE_UP pin and a FIRE_DOWN pin of the TDC-GP22, and differential square wave excitation signals with the same amplitude and opposite level signals are generated at two ends of the second transducer Y2 controlled by the FIRE_DOWN pin in the switching state. The ultrasonic signal received by the first transducer Y1 reaches the transducerP and transducerN through the first switch S1, the second switch S2, the fifth switch S5 and the sixth switch S6 and is transmitted to the echo analog amplifying circuit through the differential signal network. When the forward flight time measurement is started, the EN_START pin outputs a high level "1", the switch states of S1-6 are opposite to those shown in FIG. 1, the first transducer Y1 is in a transmitting state, the second transducer Y2 is in a receiving state, and the ultrasonic signals received by the second transducer Y2 reach a differential signal network between the Transducer P and the Transducer N through the third switch S3, the fourth switch S4, the fifth switch S5 and the sixth switch S6.
Compared with a conventional transceiver circuit with the single-end grounded transducer, the invention can effectively inhibit common mode interference caused by space electromagnetic radiation to the received ultrasonic analog quantity by adopting differential signals, thereby omitting a rear-end band-pass filter circuit, simplifying the overall system structure and improving the system reliability.
Because the echo analog amplifying circuit is a secondary process to the original received signal of the ultrasonic transducer, the signal quality of the processed output determines the data precision of the whole table base table part to a great extent. As shown in fig. 2, the echo analog amplifying circuit mainly comprises a front-stage converter formed by a first operational amplifier U1 and a second operational amplifier U2, and an instrument amplifier formed by a third operational amplifier U3, a fourth operational amplifier U4 and a fifth operational amplifier U5. The operational amplifier group in the invention adopts Microchip MCP6291 operational amplifier. The design of the instrumentation amplifier mainly considers the continuous linear adjustment of the gain, and the gain is changed through a continuous variable digital resistor so as to adapt to the change of the attenuation rate of sound waves in air and fuel gas. The continuously variable digital resistors are selected to be MCPs 4252-502.
Because the frequency of 500KHz is higher, the peak detection by a general peak detection circuit can introduce larger amplitude measurement error and can not be used as the adjustment feedback basis of gain control, so that a high-precision high-frequency signal amplitude measurement circuit, namely a high-frequency peak signal holding circuit adopted in the invention, is required to be introduced. Power detector LTC5507 is an RF power detector that is used in the operating frequency range of 100kHz to 1000 MHz. The RF input voltage is peak detected using an on-chip schottky diode (i.e., the first diode in the present invention) and an external capacitor (the seventh capacitor in the present invention).
The power detector LTC5507 is used for shaping an ultrasonic signal into a low-frequency envelope signal, and then a seventh operational amplifier at the rear end is used for building a peak hold circuit to ensure that the TDC-GP22 at the rear end has enough time for AD sampling. The seventh operational amplifier U7 here employs MCP6291.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (4)
1. The continuous variable gain amplifying circuit is characterized by comprising a transceiving switching and excitation integrated circuit, an echo analog amplifying circuit and a high-frequency peak signal holding circuit, wherein the transceiving switching and excitation integrated circuit comprises a first transducer, a second transducer and a switch group, an ultrasonic signal received by the first transducer or the second transducer is transmitted to the echo analog amplifying circuit through the switch group, the echo analog amplifying circuit comprises an operational amplifier group formed by a plurality of operational amplifiers, the differential signal outputs the ultrasonic signal through the echo analog amplifying circuit and is transmitted to the high-frequency peak signal holding circuit, the high-frequency peak signal holding circuit comprises a power detector with the model of LTC5507 and a seventh operational amplifier, the ultrasonic signal is shaped into a low-frequency envelope signal through the power detector, and the low-frequency envelope signal is held for sampling through the seventh operational amplifier;
the switch groups comprise a first switch, a second switch, a fifth switch, a sixth switch, a seventh switch and an eighth switch, two ends of the first transducer are respectively connected with a public end of the first switch and a public end of the second switch, a fulcrum of the first switch is connected with a fulcrum one of the fifth switch, the public end of the fifth switch outputs a P-way signal, a fulcrum two of the first switch is selectively connected with a power supply or a ground wire through the seventh switch, a fulcrum two of the second switch is connected with a fulcrum one of the sixth switch, the public end of the sixth switch outputs an N-way signal, a fulcrum two of the second switch is selectively connected with the power supply or the ground wire through the eighth switch, and the P-way signal and the N-way signal form a differential signal to be transmitted to the echo analog amplifying circuit;
the switch group also comprises a third switch, a fourth switch, a ninth switch and a tenth switch, wherein the two ends of the second transducer are respectively connected with the common end of the third switch and the common end of the fourth switch, the second fulcrum of the third switch is connected with the second fulcrum of the fifth switch, the first fulcrum of the third switch can be selectively connected with a power supply or a ground wire through the ninth switch, the second fulcrum of the fourth switch is connected with the second fulcrum of the sixth switch, and the first fulcrum of the fourth switch can be selectively connected with the power supply or the ground wire through the tenth switch;
the first transducer and the second transducer are pairs of transducers for measuring 500KHz, and the switch group adopts an SN74LVC1G3157DCKR analog switch, wherein: the first switch to the sixth switch are controlled by a direction control signal output by an EN_START pin of the TDC-GP22 chip;
when the reverse flight time is measured, the EN_START pin of the TDC-GP22 chip outputs a low level '0', the first transducer is in a receiving state, the second transducer is in a transmitting state, the FIRE_DOWN pin of the TDC-GP22 chip controls the two ends of the second transducer to generate differential square wave excitation signals with the same amplitude and opposite level signals, and the ultrasonic signals received by the first transducer are transmitted to an echo analog amplifying circuit through differential signals formed by the P-channel signals and the N-channel signals of the first switch, the second switch, the fifth switch and the sixth switch;
when the forward flight time measurement is started, the EN_START pin of the TDC-GP22 chip outputs a high level '1', the first transducer is in a transmitting state, the second transducer is in a receiving state, and an ultrasonic signal received by the second transducer reaches a P-path signal and an N-path signal to form a differential signal through a third switch, a fourth switch, a fifth switch and a sixth switch.
2. The continuous variable gain amplifying circuit for the ultrasonic gas meter according to claim 1, wherein the operational amplifier group comprises a first operational amplifier, a third operational amplifier and a fifth operational amplifier, the P-channel signal is input to a reverse input end of the first operational amplifier, an output end of the first operational amplifier is connected with a non-inverting input end of the third operational amplifier, a first resistor and a first capacitor which are connected in parallel are arranged between the reverse input end and the output end of the first operational amplifier, the output end of the third operational amplifier is connected to a reverse input end of the fifth operational amplifier, a digital resistor is connected between the reverse input end and the output end of the third operational amplifier, and the output end of the fifth operational amplifier outputs ultrasonic signals.
3. The continuous variable gain amplifying circuit for the ultrasonic gas meter according to claim 2, wherein the operational amplifier group further comprises a second operational amplifier and a fourth operational amplifier, the N paths of signals are input to the reverse input end of the second operational amplifier, the output end of the second operational amplifier is connected with the in-phase input end of the fourth operational amplifier, a second resistor and a second capacitor which are connected in parallel are arranged between the reverse input end and the output end of the second operational amplifier, the output end of the fourth operational amplifier is connected with the in-phase input end of the fifth operational amplifier, a digital resistor is connected between the reverse input end and the output end of the fourth operational amplifier, the in-phase input end of the fifth operational amplifier is connected with a 1.5V voltage source through a tenth resistor, and the in-phase input end of the first operational amplifier and the in-phase input end of the second operational amplifier are connected between the tenth resistor and the 1.5V voltage source through wires.
4. The continuous variable gain amplifying circuit for an ultrasonic gas meter according to claim 1, wherein the ultrasonic signal is connected to a third pin of the power detector through a sixth capacitor, the sixth pin of the power detector is connected to a non-inverting input terminal of a seventh operational amplifier, an output terminal of the seventh operational amplifier is connected to an anode terminal of the first diode, a cathode terminal of the first diode is grounded through a seventh capacitor, and a inverting input terminal of the seventh transport amplifier is connected to a cathode terminal of the first diode.
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