EP3170029A2 - Convertisseur analogique-numérique de faible puissance pour détecter des signaux de géophone - Google Patents

Convertisseur analogique-numérique de faible puissance pour détecter des signaux de géophone

Info

Publication number
EP3170029A2
EP3170029A2 EP15826074.5A EP15826074A EP3170029A2 EP 3170029 A2 EP3170029 A2 EP 3170029A2 EP 15826074 A EP15826074 A EP 15826074A EP 3170029 A2 EP3170029 A2 EP 3170029A2
Authority
EP
European Patent Office
Prior art keywords
analog
digital
input
feedback
loop filter
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP15826074.5A
Other languages
German (de)
English (en)
Inventor
John L. Melanson
Rahul Singh
Prashanth Drakshapalli
Dale Brummel
Stephen T. Hodapp
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Cirrus Logic Inc
Original Assignee
Cirrus Logic Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US14/636,417 external-priority patent/US9335429B2/en
Application filed by Cirrus Logic Inc filed Critical Cirrus Logic Inc
Publication of EP3170029A2 publication Critical patent/EP3170029A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M3/00—Conversion of analogue values to or from differential modulation
    • H03M3/30—Delta-sigma modulation
    • H03M3/39—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators
    • H03M3/412—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators characterised by the number of quantisers and their type and resolution
    • H03M3/422—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators characterised by the number of quantisers and their type and resolution having one quantiser only
    • H03M3/424—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators characterised by the number of quantisers and their type and resolution having one quantiser only the quantiser being a multiple bit one
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M3/00—Conversion of analogue values to or from differential modulation
    • H03M3/30—Delta-sigma modulation
    • H03M3/458—Analogue/digital converters using delta-sigma modulation as an intermediate step
    • H03M3/494—Sampling or signal conditioning arrangements specially adapted for delta-sigma type analogue/digital conversion systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/16—Receiving elements for seismic signals; Arrangements or adaptations of receiving elements
    • G01V1/18—Receiving elements, e.g. seismometer, geophone or torque detectors, for localised single point measurements
    • G01V1/181—Geophones
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/06—Continuously compensating for, or preventing, undesired influence of physical parameters
    • H03M1/0617—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence
    • H03M1/0634—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence by averaging out the errors, e.g. using sliding scale
    • H03M1/0656—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence by averaging out the errors, e.g. using sliding scale in the time domain, e.g. using intended jitter as a dither signal
    • H03M1/066—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by the use of methods or means not specific to a particular type of detrimental influence by averaging out the errors, e.g. using sliding scale in the time domain, e.g. using intended jitter as a dither signal by continuously permuting the elements used, i.e. dynamic element matching
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M3/00—Conversion of analogue values to or from differential modulation
    • H03M3/30—Delta-sigma modulation
    • H03M3/38—Calibration
    • H03M3/386—Calibration over the full range of the converter, e.g. for correcting differential non-linearity
    • H03M3/388—Calibration over the full range of the converter, e.g. for correcting differential non-linearity by storing corrected or correction values in one or more digital look-up tables
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M3/00—Conversion of analogue values to or from differential modulation
    • H03M3/30—Delta-sigma modulation
    • H03M3/39—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators
    • H03M3/436—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators characterised by the order of the loop filter, e.g. error feedback type
    • H03M3/438—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators characterised by the order of the loop filter, e.g. error feedback type the modulator having a higher order loop filter in the feedforward path
    • H03M3/454—Structural details of delta-sigma modulators, e.g. incremental delta-sigma modulators characterised by the order of the loop filter, e.g. error feedback type the modulator having a higher order loop filter in the feedforward path with distributed feedback, i.e. with feedback paths from the quantiser output to more than one filter stage

Definitions

  • ADCs Analog-to-Digital Converters
  • a geophone is a device for converting ground movement (displacement) into an electrical signal, which may be recorded at a recording station.
  • the deviation of this measured signal from the base line is called the seismic response and is analyzed to determine structure of the earth.
  • Geophones are used by seismologists to study the earth and are also used in oil and gas exploration to map underground structures and locate oil and gas deposits.
  • Geophones may also be used for other purposes, including alarm systems and military applications, where ground motion may detect movement of people or vehicles.
  • geophones have a very broad market in data acquisition technology.
  • the accelerometers used in earth movement monitoring are large 0 to 10Hz geophones and are distributed all over the globe in autonomous-nodal stations to study and forewarn of disastrous earth movements.
  • Smaller versions are required in buildings in areas like Japan to study the infrastructure when earthquakes and aftershocks occur. There are many placed per floor and permanently deployed. Large machinery like turbines may require geophones to monitor the bearings, armatures, and the like for cracks/wear and for proactive maintenance.
  • Geophones have historically been analog devices and originally comprised a spring-mounted magnetic mass moving within a wire coil to generate an electrical signal. In more recent times, geophones have utilized a wire coil connected to a spring or springs, which allow the coil to move over a stationary magnet. Geophones are based on an inertial mass (proof mass) suspended from a spring. They function much like a microphone or loudspeaker, with a magnet surrounded by a coil of wire. In modern geophones, the magnet is fixed to the geophone case, and the coil represents the proof mass.
  • the frequency response of a geophone is that of a damped sinusoid, mainly determined by corner frequency (typically around 10 Hz) and damping (typically 0.707). Because the corner frequency is proportional to the inverse root of the moving mass, geophones with low corner frequencies ( ⁇ 1 Hz) become impractical. It is possible to lower the corner frequency electronically at the price of higher noise and cost.
  • ADC analog-to-digital converter
  • Traditional geophone sensors measured voltage at the geophone, rather than current. As the signal is a very low power signal, it may tend to be noisy and difficult to measure, as the sensor needs to detect small variations in voltage.
  • an amplifier amplifies the output voltage of the geophone. The amplified output is then digitized by a high-resolution ADC. The amplifier is needed to sense the geophone signals, as the signals are weak and noisy.
  • a parallel resistor may provide for a known load. However, such amplifiers may require additional power, which may not be available, particularly for battery-operated and remote installations.
  • the geophone collects data from its resonant frequency to the point where mechanical limitations start to set in. Therefore, by removing a damping resistor, the benefits may be twofold.
  • One benefit is that it may eliminate certain thermal (Johnson) noise, and another benefit is that it may control the resonant frequency via the feedback current.
  • This control allows the moving coil sensor to lower the bandwidth to l-2Hz, which expands the recordable bandwidth and obtains the sub-lOHz signal that the oil exploration industry may be interested in. It is believed that Schlumberger, among others, have implemented the moving coil geophone accelerometer and have proven its benefits.
  • One problem with these systems involves acquiring data at ultra-low power while maintaining the fidelity of the sensor.
  • Electrical current produced by a moving coil geophone is very small (e.g., substantially 3.3 mA or less) and thus needs to be amplified in traditional data acquisition circuits.
  • a programmable gain amplifier is used typically to amplify the geophone signals.
  • the programmable gain amplifier demands power from the power supply, which in a geophone installation could be a battery or a long cable. It would be desirable to eliminate the programmable gain amplifier from a geophone instrumentation design in order to reduce power consumption. It would also be desirable to address one or more other shortcomings referenced here, each of which is by way of example only.
  • Figure 1A is a circuit block diagram of a first example embodiment geophone system having a single-ended input and a low-power analog-to-digital converter, in accordance with embodiments of the present disclosure
  • Figure IB is a circuit block diagram of a second example embodiment geophone system having differential-ended inputs and a low-power analog-to-digital converter, in accordance with embodiments of the present disclosure
  • Figure 2A is a circuit block diagram of an example embodiment of a low-power analog-to-digital converter having a single-ended input and a feedback digital-to-analog (DAC) path, in accordance with embodiments of the present disclosure
  • Figure 2B is a circuit block diagram of the low-power analog-to-digital converter of Figure 2A and provides more details for the loop filter, in accordance with embodiments of the present disclosure
  • Figure 2C is a circuit block diagram of the low-power analog-to-digital converter of Figure 2B and provides more details for the rest-of-the-loop-filter, in accordance with embodiments of the present disclosure
  • Figure 3 is a circuit block diagram of a further example embodiment of a lower power analog-to-digital converter, in accordance with the present disclosure
  • Figure 4 is a circuit block diagram of an example isolation network that can be used between the geophone sensor and the first stage of the low-power analog-to-digital converter of the geophone system of Figure ⁇ , ⁇ , 6A, and/or 7, in accordance with embodiments of the present disclosure;
  • Figure 5 is a circuit block diagram illustrating a front-end portion of a geophone system in accordance with the prior art
  • FIG. 6A is a circuit block diagram of an example embodiment geophone system having a low-power ADC that has a single-ended input and a feedforward path only, in accordance with embodiments of the present disclosure
  • Figure 6B is a circuit block diagram of an example embodiment feedback DAC that can be used as the feedback DAC in the example geophone system of Figure 6A;
  • Figure 6C shows a circuit block diagram of an example embodiment quantizer that can be used as the quantizer in the example geophone system of Figure 6A;
  • FIG. 7 is a circuit block diagram of an example embodiment of a third-order geophone system with differential-ended inputs wherein the third-order geophone system has a low-power ADC that has differential-ended inputs and feedback DACs, in accordance with embodiments of the present disclosure.
  • Figure 8 is a circuit block diagram of an example resistor feedback DAC that can be used as the feedback DAC(s) in the geophone sensor system of Figure 7.
  • one or more disadvantages and problems associated with existing approaches to converting low-power analog signals into digital signals may be reduced or eliminated.
  • a low power analog-to- digital converter configured to sense sensor signals may include a loop filter and a feedback digital-to-analog converter.
  • the loop filter may have a loop filter input configured to receive an input current signal from a sensor and generate an output signal responsive to the input current signal.
  • the feedback digital-to-analog converter may have a feedback output configured to generate a current-mode or charge-mode feedback output signal responsive to the output signal, the feedback output coupled to the loop filter input in order to combine the input current signal and the feedback output signal at the input.
  • a method for sensing sensor signals may include receiving an input current signal from a sensor in a loop filter having a loop filter input. The method may also include generating an output signal responsive to the input current signal by the loop filter. The method may additionally include generating one of a current-mode feedback output signal or a charge-mode feedback output signal responsive to the output signal. The method may further include combining the input current signal and the feedback output signal at the loop filter input.
  • FIGURE 1A is a circuit block diagram of a first embodiment geophone system having a single-ended input and a low-power analog-to-digital converter, such as current-mode delta-sigma modulator analog-to-digital converter (CM ⁇ ADC) 14a.
  • CM ⁇ ADC current-mode delta-sigma modulator analog-to-digital converter
  • resistance from resistor R may be provided in line into a multiplexer (mux).
  • Resistor R may be split internally and externally to the current-mode delta-sigma analog-to- digital converter 14a, and thus may represent the combination of internal and external resistances.
  • the series resistor R may represent any combination of resistances, internal and external to the integrated circuit that would embody CM ⁇ ADC 14a as would be understood by those of ordinary skill in the art.
  • resistance R may represent a combination of an internal resistance of 100 ohms and an external resistance of 900 ohms in one application. In another application, no external resistance may be present, thus providing different overall impedance. In general, it is desirable to keep the resistance low, as less thermal noise is added, and the over-damped geophone has less mechanical motion, thereby producing lower distortion.
  • the preferred total input impedance is on the order of 50 ohms per input.
  • One purpose for using a mux in a seismic recording system is to disconnect the sensor so the data acquisition system and the sensor can be tested.
  • Some sensor manufacturers have experimented with testing the sensor and the signal processing hardware (e.g., amplifier, analog-to-digital converter, signal filter, and the like) all at the same time.
  • the signal processing hardware e.g., amplifier, analog-to-digital converter, signal filter, and the like
  • providing a mux in the design may provide the user with both options - testing the sensor by itself, or in conjunction with the signal processing hardware.
  • Using a mux for multiple sensors may not be as feasible for seismic exploration but may be useful for monitoring machine health, or other applications.
  • Embodiments of low-power analog-to- digital converters may integrate the ADC with the sensor, thus creating a "smart sensor” that operates using low power while still maintaining and verifying required dynamic range (low noise and distortion) for most common applications.
  • the mux may or may not be included, depending on the application.
  • a geophone sensor, transducer, or other low-power output instrument or sensor is shown or represented as element 10, outputting a time- varying current signal in response to mechanical vibrations or movement, such as movements of the earth.
  • the term "low-power” as used in the present application refers to instruments and components outputting low-power signals and/or having low-power usage requirements, on the order of lOmW or less.
  • the output signal from the geophone may be a low-voltage, low-power signal.
  • such instruments may be remotely located or battery powered, they may have lower power consumption requirements as well.
  • the present invention may be applied to other types of instruments where energy savings or other features of the invention as described herein are advantageous.
  • FIGURES 1A, IB may represent a boundary between geophone or other low-power output instrument or sensor 10 and an integrated circuit housing a low-power analog- to-digital converter, in the one embodiment.
  • the elements of the low-power analog-to-digital converter may be provided as discrete components or the package may be integrated into a geophone or other instrumentation device. Other arrangements or configurations may also be apparent to one of ordinary skill in the art having the benefit of the present disclosure.
  • Current-mode delta-sigma analog-to-digital converter 14a may measure the current output IQP produced by the geophone or other instrument and then may output a digital signal. This digital signal, which may be representative of earth vibrations or movement, or other signal types, may then be communicated to a digital circuit 16a for data logging, analysis, alarm functions, and/or other uses commonly known for such geophone or other sensor data.
  • Traditional geophone sensors measure voltage at the geophone, rather than current. As the signal is a very low-power signal, it may tend to be noisy and difficult to measure, as the sensor needs to detect small variations in voltage.
  • Output terminal 12a of geophone or other low-power output instrument or sensor 10 may be coupled in line to resistor R, the mux, and the current-mode delta-sigma analog-to-digital converter 14a.
  • Current- mode delta-sigma analog-to-digital converter 14a may have either a current- mode or a charge-mode feedback.
  • the value for the resistor R may be selected in such a way so that the transducer or geophone sensor may be designed to experience constant or substantially constant (e.g., within measurable limits) low impedance, as practically possible.
  • FIGURE IB is a circuit block diagram of a second embodiment geophone system having differential-ended inputs and a low-power analog-to-digital converter.
  • the second embodiment geophone system of FIGURE IB may be simlar to the first embodiment geophone system of FIGURE 1A, so only differences will be discussed. The main difference is that the second embodiment geophone system has differential-ended inputs while the first embodiment geophone system has a single-ended input.
  • Current output IQP of the geophone device may not be measured at a single output terminal 12a but may instead output through differential output terminals 12b and 12c. Differential output terminals 12b and 12c may in turn each respectively couple in line with a resistor R' and a mux as shown in FIGURE IB.
  • Output terminal 12b of geophone or other low-power output instrument or sensor 10 may be coupled in line to a resistor R', a mux, and the current-mode delta-sigma analog-to-digital converter 14b.
  • Output terminal 12c of geophone or other low-power output instrument or sensor 10 may be coupled in line to another resistor R' , another mux, and the current-mode delta-sigma analog-to-digital converter 14b.
  • the current- mode delta-sigma analog-to-digital converter 14b may have either a current-mode or a charge-mode feedback.
  • the values for the resistors R' may be selected in such a way so that the transducer or geophone sensor may be designed to experience constant or substantially constant (e.g., within measurable limits) low impedance, as practically possible.
  • the advantage of differential operation may be generally lower noise for a given power and more immunity to common-mode noise.
  • the transducer or a geophone sensor, or other low-power output instrument or sensor is shown as element 10, outputting a variable current signal in response to vibrations or movement of the earth.
  • Current output of the transducer or geophone sensor or other low-power output instrument or sensor 10 may be measured at output terminals 12b and 12c of the transducer, or geophone sensor, and/or other low-power output instrument or sensor 10, which may be a terminal present on a sensor packaging or wire leads from a sensor or the like.
  • Current-mode delta-signal analog-to-digital converter 14b may measure the current output IQP produced by the geophone or other instrument and may then output a digital signal indicative of this current output.
  • This digital signal which may be representative of earth vibrations or movement, or other signal types, may then be communicated to a digital circuit 16b for data logging, analysis, alarm functions, or other uses commonly known for such transducer, geophone, or other sensor data.
  • FIGURES 2A to 2C disclose circuit block diagrams that illustrate an example low- power analog-to-digital converter (“ADC") having a single-ended input, in accordance with the present disclosure.
  • FIGURE 2A shows the low-power ADC having a loop filter 36a, a quantizer (Q) 30a, and a feedback digital-to-analog converter (DAC) 32a.
  • Current IQP from geophone sensor, or the transducer, or other low-power output instrument or sensor 10 may be provided directly as an input current to loop filter 36a.
  • the input current directly from the transducer or sensor may be provided to a first stage or first integrator of the loop filter 36a, and such current into the first stage or first integrator may cause and generate the digital feedback signal that may be fed into feedback DAC 32a.
  • the feedback path in the embodiment of FIGURE 2A may be implemented as a charge-mode feedback path or a current-mode feedback path.
  • FIGURE 2B is a circuit block diagram of the low-power analog-to-digital converter of FIGURE 2A, and FIGURE 2B provides more details for the loop filter 36a.
  • Loop filter 36a may have a first stage with an operational amplifier integrator 28a, a capacitor C, and a rest-of- the-loop-filter 26a coupled in the manner and configuration shown in FIGURE 2B in accordance with the embodiment(s) of the present disclosure.
  • the negative input terminal of integrator 28a may receive the current IQP directly from the transducer or geophone sensor, and the positive input terminal of integrator 28a may be grounded.
  • FIGURE 2C is a circuit block diagram of the low-power analog-to-digital converter of FIGURE 2B, and FIGURE 2C provides more details for the rest-of-the-loop-filter 26a.
  • the rest-of-the-loop-filter 26a may have a second stage with an operational amplifier integrator 28a", another capacitor C, resistors R", and a feedback DAC 32a", and a third stage with an operational amplifier integrator 28a'", yet another capacitor C, resistors R'", and a feedback DAC 32a'", coupled in the manner and configuration as shown in FIGURE 2C.
  • the output of quantizer (Q) 30a may respectively be fed into the second and third stages via DACs 32a' ' and 32a' ' ' as shown in FIGURE 2C.
  • the loop order is three or a third order.
  • the design of loop filters and noise transfer functions is well understood by those skilled in the art. This topology is called a third-order feedback-type, and may have the advantage of high imunity to high-frequency noise.
  • a charge-mode feedback digital-to-analog converter 32a may make the geophone system less sensitive to jitter in clock output but may introduce a transient behavior into the virtual ground Vg.
  • This jitter problem may be solved, such as taught and disclosed in U.S. Patent No. 5,896,101 to Melanson, issued on April 20, 1999, entitled “Wide Dynamic Range Delta Sigma AID Converter” and incorporated herein by reference.
  • charge-mode and current-mode may be used interchangably.
  • FIGURE 3 shows a circuit block diagram of a further example embodiment of a low-power ADC, in accordance with the present disclosure.
  • the low-power ADC in FIGURE 3 may be similar to the low-power ADC in FIGURE 2B.
  • the low-power ADC in FIGURE 3 may have a loop filter 36b, a quantizer (Q) 30b, and a feedback DAC 32b coupled in the manner shown in FIGURE 3.
  • loop filter 36b may have a first transconductance gain stage 28b.
  • the first transconductance gain stage 28b may have a capacitor Cf coupled across its differential inputs.
  • the negative differential input of the first transconductance gain stage 28b may receive the current input IGP from geophone sensor, or the transducer, or other such sensor.
  • the positive diffential input of the first transconductance gain stage 28b may be grounded.
  • the first transconductance gain stage 28b may also have an RC network comprising a resistor Rz and a capacitor C coupled across its output.
  • First transconductance gain stage 28b may be coupled to a rest-of-the-loop-filter 26b as shown in FIGURE 3.
  • FIGURE 4 shows an example optional isolation network that may be used between the transducer or geophone sensor or other such sensor and the first stage of the low- power ADC of the geophone system, such as the geophone system of FIGURE 1 A or IB, in accordance with embodiments of the present disclosure.
  • the example isolation network has resistors Ri and R 2 , capacitors Ci and C 2 , and inductor L coupled in the manner shown in FIGURE 4.
  • the example isolation network is optional and is not required. If used, the example isolation network could be coupled between the transducer or geophone sensor or other such sensor and the mux shown in FIGURE 1A or IB.
  • the isolation network may allow the first integrator to operate at the lowest possible power without adding additional noise in the signal band.
  • FIGURE 5 shows a circuit block diagram that illustrates a front end portion 500 of a geophone system in accordance with the prior art.
  • Front end geophone system portion 500 shows a transducer or geophone sensor or other such sensor 10 coupled to a preamplifier 502.
  • Preamplifier 502 has a capacitor C coupled across its input and output as shown in FIGURE 5.
  • the preamplifier 502 operates as a current-to-voltage converter (I-to-V converter) or a transimpedance amplifier for the geophone system of FIGURE 5 to receive the geophone input signals.
  • I-to-V converter current-to-voltage converter
  • Preamplifier 502 is coupled to a first stage or first integrator 28a of the loop filter of the ADC, and the loop filter is in turn coupled to the rest of the loop filter or delta-sigma modulator.
  • the output of the loop filter is coupled to the digital filter 16a.
  • Operating current is required for both the preamplifier and the ADC, and both contribute noise to the output.
  • Western Geco UniQ integrated point-receiver land seismic system and Japanese Patent No. P3098045 provide examples of such a premplifier and ADC geophone system configuration.
  • All of the example embodiments of the geophone systems and low-power ADCs as provided in accordance with the present disclosure may eliminate having to use a preamplifier, I-to-V converter, and/or transimpedance amplifier between the transducer/sensor and the ADC.
  • FIGURE 6A shows a circuit block diagram of an example embodiment geophone system 600 having a low-power ADC that has a single-ended input and a feedforward path only, in accordance with embodiments of the present disclosure (e.g., single-ended, feedforward geophone system topology).
  • the geophone sensor 10 may be referenced to ground, and the current output of the geophone sensor 10 may be fed directly as an input into the first stage or first integrator INTl having an operational amplifier integrator 28a and a capacitor CI coupled in the manner shown in FIGURE 6A.
  • the first stage or first integrator INTl may be coupled in series with second and third stages/integrators INT2 and INT3 in the manner shown in FIGURE 6A.
  • Second stage/integrator INT2 may have an operational amplifier integrator 28a' ' , a resistor R2, and a capacitor C2 coupled in the manner shown in FIGURE 6A, while the third stage/integrator INT3 may have an operational amplifier integrator 28a'", resistor R3, and capacitors C3 and C4 coupled in the manner shown in FIGURE 6A.
  • the outputs of first stage/integrator INTl and the third stage/integrator INT3 may be fed into a summer 602 as shown in FIGURE 6A.
  • the output of the summer 602 may be fed into quantizer (Q) 30a.
  • Q quantizer
  • the significant advantage of this topology may be the reduction of noise and power by the joining of the amplifier with the ADC.
  • the key characteristic of the circuit may be the balancing of the geophone current with the current DAC feedback current, and the delta-sigma conversion ensuring that balance.
  • the output of quantizer (Q) 30a may be provided as an output to a correction block 504 and a digital filter 16a and also fed back to a scramble block 506 and feedback DAC 32a as shown in FIGURE 6A.
  • Example correction, calibration, and/or compensation operations, techniques, and/or methods for the correction block 504 are disclosed in U.S. Patent No. 6,449,569 to Melanson (hereafter “the '569 patent") entitled "CALIBRATION AND COMPENSATION OF DELTA SIGMA ADC'S AND DAC'S BY CORRELATING NOISE SIGNALS,” and incorporated by reference herein.
  • example scramble operations, techniques, and/or methods for the scramble block 506 are disclosed in U.S.
  • scramble block 506 may scramble selection of digital-to- analog elements of the feedback digital-to-analog converter (e.g., selection of individual switched current supplies of FIGURE 6B, selection of resistor DAC elements of FIGURE 7).
  • the low-power ADC in geophone system 600 may be a feedforward design for the low-power ADC.
  • an input from each of the stages/integrators would often be fed to the summer 602.
  • one of the input paths to the summer 602 may be replaced by the function of capacitor C3.
  • FIGURE 6B shows a circuit block diagram of an example embodiment feedback DAC that may be used as the feedback DAC 32a in the example geophone system 600.
  • Example feedback DAC 32a may comprise a number of current sources SO, SI, S2 S31, and the current sources may generally be configured as shown in FIGURE 6B. Each current source may comprise a field-effect transistor (FET) current mirror, or similar system.
  • FIGURE 6C shows a circuit block diagram of an example embodiment quantizer (Q) that may be used as the quantizer (Q) 30a in the example geophone system 600.
  • Example quantizer (Q) 30a may comprise a voltage reference string(s) RS and thirty-two (32) comparators CP0, CP1,...., CP30, CP31 coupled in the manner shown in FIGURE 6C.
  • the number of current sources, and quantization levels, is a design choice, with four to sixty-four (4-64) levels being typical for a high performance system.
  • Geophone system 600 may operate in a current mode and may have a feedback loop that cancels the geophone input current with the current of the feedback DAC 32a. Geophone system 600 may eliminate the need to have a preamplifier, I-to-V converter, and/or transimpedance amplifier between the geophone sensor/transducer and the low-power ADC. Geophone system 600 is only one example of many examples and topologies that can implement such a scheme or system.
  • FIGURE 7 shows a circuit block diagram of an example embodiment of a third- order geophone system 700 with differential-ended inputs.
  • the third-order geophone system 700 may have a low-power ADC that has differential-ended inputs and feedback DACs, in accordance with embodiments of the present disclosure.
  • the topology shown in FIGURE 7 is often referred to as a feedback topology.
  • the topology may have a low-pass signal transfer function (STF).
  • STF low-pass signal transfer function
  • NTF third-order noise-to-transfer function
  • resistor DACs 32a, 32a", and 32a' ' ' may be used and may provide the feedback DACs for respective first, second, and third integrator stages.
  • One RDAC may be provided and used for each stage.
  • the choice of order, topology, and NTF is a well-understood design space trade-off.
  • Example geophone system 700 may be fully differential which may provide good external noise rejection.
  • Geophone sensor 10 may be coupled to differential inputs 12b and 12c and respective in-line resistors R' to a loop filter as shown in FIGURE 7.
  • the loop filter may include first, second, and third integrator stages (1 st INT STAGE, 2 nd INT STAGE, 3 rd INT STAGE) as shown in example geophone system 700.
  • the loop filter may have differential outputs that feed into example quantizer 30a.
  • Quantizer 30a comprises thirty-two (32) comparators that provide thirty-two (32) outputs to a digital filter 16a. Correction for the digital output signals from quantizer 30a being fed into the digital filter 16a may be provided by a digital correction block 504.
  • digital correction block 504 may be coupled between quantizer 30a and digital filter 16a.
  • calibration of the digital signals into digital filter 16a may be accomplished through a calibration logic block 702 and a scramble block 506 that are coupled in the manner shown in example geophone system 700.
  • the '569 patent and the Scramble Applications provide respective example calibration and scramble operations, techniques, and/or methods for the corresponding calibration logic block 702 and the scramble block 506.
  • the calibration logic block 702 may be used to linearize the geophone system 700 by determining the ratios of DAC resistors, the values of which are used in the digital filter 16a.
  • a dynamic-element-matching (DEM) block can be used in place of the scramble block 506. Such a DEM block may remove the need for the calibration logic block 702 but, on the other hand, may increase susceptibility to inter- symbol interference (ISI).
  • the output of quantizer 30a may be fed back to the first, second, and third integrator stages through respective feedback resistor DACs 32a, 32a", and 32a' " as shown in example geophone 700.
  • FIGURE 8 shows an example resistor feedback DAC (RDAC) 800 that may be used as the feedback resistor DAC 32a, 32a", and/or 32a'" in the example geophone system 700.
  • RDAC 800 comprises thirty-two (32) pairs of resistors ROA, ROB; R1A, RIB,....R30A, R30B; R31A, R31B.
  • One of the resistors in each resistor pah- may be coupled to a positive voltage reference +VREF of a transistor/switch pair and the other resistor in each resistor pair may be coupled to a negative voltage reference -VREF of the transistor pair.
  • RDAC 800 may provide thirty-three (33) levels of feedback (e.g., 0-32 levels), when each resistor unit is considered a nearly identical element to each other.
  • the timing block(s) 802 may utilize and/or provide a clock (CLOCK) that synchronizes the change of transistor switches for the transistor/switch pair(s) and may minimize the shoot-through current by non-overlapphing the transistors of the transistor/switch pair.
  • CLOCK clock
  • geophone system 700 may operate in a way so that direct feedback of current is provided by the first stage or first integrator of RDAC 32a to the signal input nodes 12b and 12c. The choice of the digital input sets the position of the switches, and therefore the feedback current.
  • the example embodiment of the low-power ADC having the single-ended input in FIGURES 2A to 2C can be used as a specific example implementation for CM ⁇ ADC 14a in the geophone system shown in FIGURE 1A.
  • the low-power ADC having differential- ended inputs in FIGURE 5 may be used as a specific implementation for CM ⁇ ADC 14b in the geophone system shown in FIGURE IB.
  • the low-power ADC in accordance with the present disclosure is configured to couple or connect to a transducer, geophone sensor, or other such sensor.
  • the low-power ADC may digitize the output of the transducer, geophone sensor, or other such sensor.
  • the transducer, geophone sensor, or other such sensor may have an output that is generally representative of mechanical motion.
  • the geophone sensor system in accordance with the present invention such as the example ones disclosed and discussed in FIGURES 1A, IB, 2C, 3, 6A, and 7, describe a system in which the transducer, geophone sensor, or other such sensor (e.g., transducer/sensor input) is driven into as low as possible/practical of an impedance.
  • the values for the in-line resistors R and R' shown in respective FIGURES 1A, IB, and 7 may be selected in a manner such that their input resistances are intentionally kept as low as possible.
  • these resistor values are limited by the stability and practical mux impedance.
  • resistor values may be selected so that the input of the geophone sensor system is designed to have a low impedance.
  • Typical values of such resistors R or R' are ten (10) ohms to one hundred (100) ohms.
  • the present disclosure is not in any way limited to the topologies or configurations of the geophone sensor system or the low-power ADCs specifically provided in this present disclosure.
  • the geophone sensor system and the low-power ADCs are not in any way limited to a respective or corresponding feedforward topology, feedback topology, a single- ended topology, and/or a differential-ended topology.

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  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Geophysics And Detection Of Objects (AREA)
  • Analogue/Digital Conversion (AREA)
  • Measurement Of Current Or Voltage (AREA)

Abstract

L'invention concerne un convertisseur analogique-numérique conçu pour détecter des signaux de détection pouvant comprendre un filtre à boucle et un convertisseur numérique-analogique à rétroaction. Le filtre à boucle peut comprendre une entrée de filtre à boucle conçue pour recevoir un signal d'entrée courant d'un capteur et pour générer un signal de sortie en réponse au signal d'entrée courant. Le convertisseur numérique-analogique peut comprendre une sortie de rétroaction conçue pour générer un signal de sortie de rétroaction en mode courant ou en mode charge en réponse au signal de sortie, la sortie de rétroaction étant couplée à l'entrée du filtre à boucle afin de combiner le signal courant d'entrée et le signal de sortie de rétroaction à l'entrée.
EP15826074.5A 2014-07-16 2015-06-17 Convertisseur analogique-numérique de faible puissance pour détecter des signaux de géophone Withdrawn EP3170029A2 (fr)

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US201462025225P 2014-07-16 2014-07-16
US201462044148P 2014-08-29 2014-08-29
US14/636,417 US9335429B2 (en) 2012-09-25 2015-03-03 Low power analog-to-digital converter for sensing geophone signals
PCT/US2015/036151 WO2016032598A2 (fr) 2014-07-16 2015-06-17 Convertisseur analogique-numérique de faible puissance pour détecter des signaux de géophone

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TW201606332A (zh) 2016-02-16

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