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WO2008060298A2 - Compensation de gain dans un émetteur-récepteur à ultralarge bande - Google Patents

Compensation de gain dans un émetteur-récepteur à ultralarge bande Download PDF

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Publication number
WO2008060298A2
WO2008060298A2 PCT/US2006/060982 US2006060982W WO2008060298A2 WO 2008060298 A2 WO2008060298 A2 WO 2008060298A2 US 2006060982 W US2006060982 W US 2006060982W WO 2008060298 A2 WO2008060298 A2 WO 2008060298A2
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WO
WIPO (PCT)
Prior art keywords
signal
frequency
gain
ultra
wideband
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.)
Ceased
Application number
PCT/US2006/060982
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English (en)
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WO2008060298A3 (fr
Inventor
Albert J. Charpentier
Gopalakrishna K. Bhat
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Intellifit Corp
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Intellifit Corp
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Publication date
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Priority to PCT/US2006/060982 priority Critical patent/WO2008060298A2/fr
Publication of WO2008060298A2 publication Critical patent/WO2008060298A2/fr
Publication of WO2008060298A3 publication Critical patent/WO2008060298A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/7163—Spread spectrum techniques using impulse radio
    • H04B1/71637—Receiver aspects
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/7163—Spread spectrum techniques using impulse radio
    • H04B1/71635—Transmitter aspects

Definitions

  • This invention relates to gain compensation in ultra-wideband transceivers.
  • this invention relates to a method to compensate for non-uniform frequency response in a transmitter/receiver system where a substantially uniform signal return level is desirable.
  • U.S. Patent No. 6,507,309 entitled Interrogation of an Object for Dimensional and Topographical Information discloses a method of determining the dimensions of a human body using electromagnetic radiation in the frequency range of about 200 Megahertz (MHz) to about 1 Terahertz (THz). Tn a most preferred form, this reference discloses a range of about 5 Gigahertz (GHz) to about 110 GHz.
  • narrow band transmission techniques are used which can avoid excessive frequency response non-uniformity.
  • narrow band systems requiring only a few MHz in bandwidth
  • the required bandwidth allows operation across a frequency range where the frequency response of the transmitter or receiver components are more closely related and component tolerances are controllable.
  • an ultra-wideband system e.g. 5GHz or more
  • tuning the frequency response of the system to be optimal is a much more challenging task because of the inherent variation of the system components over the ultra- wide frequency range.
  • AU components show some amount of gain variation when used over a wide bandwidth. But, in the ultra-wide bandwidth systems, the gain variation in the components over the frequency range can be severe.
  • the semiconductor components, cabling and antennas that are used in the total system can have gain variation in excess of 2OdB.
  • This variation reflects directly on the signal to noise quality of the system.
  • the gain variation substantial, it can occur in a relatively small region of the overall bandwidth of the system.
  • component and connection gain variations as much as 2OdB can easily be encountered in measured bandwidths as small as 0.2 GHz.
  • a system of cascaded narrow band transceivers multiplexed into the transceiver elements could be used to address the ultra-wideband gain uniformity issues addressed above. But, the solution is undesirable in terms of cost and complexity in transceiver equipment and the difficulty in mapping different bandwidth variations into useable acquisition results for postprocessing of data. Accordingly, a gain compensation mechanism is desirable to allow the use of a single transceiver to system to sweep an ultra- wideband system across its full frequency range while maintaining a reasonable and predictable transmit and receive signal level across the entire spectrum of interest.
  • a gain compensation system is used in a multi- Gigahertz bandwidth system which measures parameters of a human individual.
  • the gain compensation scheme involves a circuit that controls the output a gigahertz mixer by controlling the level of the intermediate frequency (IF) input amplitude of the gigahertz mixer.
  • the amplitude level of the IF input to the gigahertz mixer is the result of an analog multiplier.
  • One input of the analog multiplier receives a fixed level IF signal and the other multiplier input receives a gain control signal.
  • the circuit operates by sending gain values stored in a memory to a digital-to-analog (D/ A) converter.
  • the analog output of the D/A converter is the gain control signal sent to the analog multiplier.
  • the gain control values are obtained by measuring the uncompensated frequency response of the ultra- wideband transceiver when a flat, stationary target is presented to the combination transmit/receive antenna array.
  • the overall system frequency response is obtained from transmitter through to the final receiver and mixer down to the baseband output of a quadrature receiver.
  • a table of this complete frequency response is created representing the amplitude response of the uncompensated system.
  • a corresponding inverse and scaled table is then generated representing the gain compensated values. These values may be stored in the gain table. When utilized, the gain table dramatically improves the flatness of the system response over the desired bandwidth of the system.
  • Figure 1 is a functional block diagram of an example ultra- wideband system used for measuring the form of an individual
  • FIG. 1 is block diagram of an example ultra- wideband system transceiver
  • Figure 3 is a block diagram of a circuit embodiment having aspects of the invention.
  • Figure 4a graphically depicts the frequency response of an uncompensated system
  • Figure 4b graphically depicts the frequency response of a compensated system
  • Figure 5 is a flow diagram of a method having aspects of the invention.
  • Figure 1 depicts an example ultra- wideband system 100. Although many applications of an ultra- wideband system are possible, Figure 1 depicts a system for the measurement of physical characteristics of an individual. This specific example system 100 acquires data representative of reflections of electromotive (EM) energy from an individuals' body. The system includes an area 120 where an individual 110 would stand while low level EM energy is transmitted, reflected off the individuals body, and received. However, it will be noted that aspects of the invention may be used in any suitable ultra-wideband system.
  • a frequency and gain control function 102 is used to control the level of RF energy used to feed the transmission equipment 104. The function of the frequency and gain control is to provide gain compensation over the wide bandwidth of the ultra- wideband system 100.
  • the system 100 operates by transmitting across an ultra- wideband of frequencies in a multiple sweeps or "chirps". The chirps or sweeps are performed periodically as the array is moved over the stationary individual.
  • An antenna multiplexer 106 selects a transmit and receive antenna pair that transmits and receives the sweep of frequencies within the chirp.
  • Variations in the received signal correspond to the distance of the "reflective" portions of the individuals body from the antenna array 108. Reflected signals are received by the receive portion of the antenna array 108, are demultiplexed 106 and processed by the RF receiver equipment 112.
  • Variations in the received signals are then processed, either in real-time or by post processing 114 to derive a three dimensional image of the individual 110.
  • a sweep may occur over the frequency range of 9.5 to 17.5 GHz. This sweep is chirped in a burst in less than 30 microseconds and is repeated continuously as the array is moved around the individuals body to map the reflections of the individual as seen in a 360 degree rotation.
  • the gain of the transmit chirp is not naturally gain-uniform because the frequency response or tuning of the system components is not linear over the entire chirp frequency range.
  • the decreasing amplitude response of the system as the each chirp reaches higher frequencies would result in loss of reflected signal from the individuals body, thus resulting in reflective data loss at higher frequencies.
  • gain compensation of the ultra-wideband system 100 is most desirable.
  • FIG. 2 is a block diagram of an example ultra- wideband system 200 configured to accommodate the gain compensation needs of Figure 1.
  • the system 200 controls the gain of the intermediate frequency (IF) signal input to mixer 212 to control the gain of a the transmit signal across the ultra-wideband frequency range of each chirp produced by the system.
  • the transmission portion of the system 200 includes a look up table (LUT) 202 to control a digital to analog (D/ A) converter 204 which exercises a voltage controlled oscillator (VCO) 206.
  • the VCO 206 is used to generate the sweep of frequencies needed for the ultra- wideband system chirp.
  • Voltage controlled oscillators have analog inputs and may be nonlinear in their voltage to frequency conversion.
  • swept frequencies are controlled by varying the analog input.
  • the linearity of the VCO 206 may be controlled by the look up table supplying digital control values to the D/A converter 204 corresponding to the frequency ramp desired.
  • the VCO 206 may be controlled by the D/A converter to produce a frequency range of 4.75 GHz to 8.75 GHz.
  • a frequency doubler 208 is used to bring up the chirp frequency sweep up to 9.5 GHz to 17.5 GHz.
  • the sweep of frequencies enters a power splitter 210 to feed a mixer 212 and a feedback delay line 244.
  • the mixer 212 combines an IF signal and the sweep of frequencies emerging from the frequency doubler 208 via the splitter 210.
  • the analog level of the TF input to the mixer 212 is varied to accommodate the falloff of frequency response of the RF elements of the system 200 as frequencies increase within a chirp.
  • an IF frequency of 68 MHz is used as a local oscillator (LO) 242.
  • the LO is used by both the transmitter portion of the transceiver system 200 and the receiver portion via a power splitter 240.
  • the LO signal 241 is used to feed a multiplier 238.
  • the IF signal amplitude is varied by controlling a second input to the multiplier 238.
  • This second input is a control voltage input varied by a look up table 234 providing digital input values for a D/A converter.
  • values of the look up table 234 are programmed to vary the magnitude of the control voltage input of the multiplier 238.
  • the D/A converter 236 essentially provides a gain control input for the fixed-level 68 MHz LO.
  • the output of the multiplier 241 is an TF signal whose magnitude is controlled via the look up table 234.
  • the look up table is programmed to compensate for the high frequency drop in magnitude of the chirp signal.
  • the output of the mixer 212 is a ultra-wideband frequency swept output with an output signal level which compensates for the non-uniform gain characteristic in the frequency response of the RF components of the transceiver system 200.
  • the ultra-wideband signal at the output of the mixer 212 is amplified 214 and routed via an element mux 216 to a transmit element in the transmit array 218.
  • the ultra- wideband transmit wavefront is reflected off of the individual's body 110 and sensed by a selected receive element in the receive array.
  • a receive element in the receive array 218 collects the reflected signals.
  • the collected signals are routed via mux 220 to an low noise amplifier 222 and are presented for downconversion.
  • Mixer 224 combines the received signal from the low noise amplifier 222 and a copy of the ultra- wideband signal from amplifier 246 and produces an IF result.
  • the copy of the ultra- wideband signal was obtained from the output of the frequency doubler via a power splitter 210.
  • a delay line 244 is inserted in the system 200 so as to accommodate the travel time and distance that the ultra- wideband signal traverses to get to the mixer 224.
  • the delay line provides an equivalent of 17 feet of signal delay so that a phase correlated downconversion of the received reflection signal may occur.
  • a 70MHz bandpass filter 226 is employed to filter out the unwanted mixer products and the result is amplified 228 before being provided to a 70MHz quadrature receiver 230. I and Q channels may be extracted and provided to an A/D converter 232 so that the digitized data can be processed.
  • a calibration of the gain of the ultra-wideband signal over the frequency range of one chirp is made. Tn one embodiment, a system calibration is performed after the initial build and prior to use as a human body profiler.
  • the calibration data may be provided into RAM memory which drives the D/A converter 236 used to modulate the gain of the IF multiplier 238.
  • the calibration includes supplying the gain curve with a flat (DC) table of approximated 25% of full RF power.
  • the overall system response is obtained, from the transmitter 214 through to the final receiver and mixer down to the baseband I and Q signal output of the 70 MHz quadrature receiver 230.
  • the complete response of the system over the ultra- wide bandwidth is characterized and a table is created representing the amplitude response of the system.
  • An inverse table of the amplitude information is then stored in the look up table 234 that drives the D/A converter 236.
  • the gain calibration compensates for the falloff of gain at the high frequencies of the chirp and dramatically improves the flatness of the system response over the entire desired bandwidth of the system.
  • FIG. 3 is an example embodiment of the gain compensation mechanism 300 of the present invention.
  • a digital counter 310 is driven by a clock oscillator 324 to provide a ramp of digital counts useful as an address for memory.
  • RAM 312 is used as a look up table corresponding to the LUT 202 of Figure 2.
  • RAM 312 provides the linearity compensation for the voltage controlled oscillator 316 which drive the frequency doubler 208.
  • the counter simultaneously provides an address reference to RAM 318 which contains the gain compensation look up table.
  • the RAM 318 drives the D/A converter 320 to provide an analog input to the four quadrant multiplier 322. This analog multiplier also inputs the fixed-level LO frequency so that the output of the multiplier is a controlled level LO output to drive the ultra-wideband mixer previously discussed.
  • the single synchronous counter can provide the same address information to control the responses of both the voltage controlled oscillator 316 as well as the analog multiplier 322.
  • the swept frequency and the gain compensation are synchronized.
  • a CPU and control logic 326 provides the overall timing and event control for the gain compensation circuitry 300 as well as the rest of the system 200.
  • the gain compensation mechanism accommodates normal variations in the build of the ultra-wideband system that affects frequency response. The goal is to obtain an ultra- wideband transmission signal that has a nearly uniform or flat gain characteristic across the entire frequency sweep of the chirp.
  • the flatness or improved uniformity of the gain characteristic in the frequency response of the system components may be measured by examining the I and/or Q channels of the 70 MHz quadrature receiver. During such a frequency response measurement, the human target is replaced with a flat panel reflector. Using a flat, known reflectivity target removes signal length, attenuation variation, and shape variations from affecting both the amplitude and phase response of the system.
  • Figure 4a is an example depiction of a frequency response of the system after VCO 316 calibration but before gain compensation.
  • the Figure 4a response is indicative of the frequency response of the system viewing a single chirp against a flat and stationary calibration target.
  • the I channel response 410 indicates that there is a notable amplitude fall-off as frequency increases in the chirp sweep.
  • the Q channel response 420 would be similar but have a 90 degree phase shift.
  • the uncompensated power level 430 is calculated as SQRT (I 2 +Q 2 ).
  • Figure 4b depicts the same system configuration after gain compensation.
  • RAM 318 was loaded with values commensurate with an increased gain across the frequency sweep of the chirp.
  • the I channel result 450 after compensation indicates a more uniform gain response across the frequency sweep of a single chirp.
  • the corresponding Q channel result 460 is similar with a 90 degree phase shift.
  • the compensated power level 470 is calculated as SQRT (I 2 +Q 2 ). The more stable and flat the frequency response, the easier it is to extract frequency and amplitude variations which correspond to contours of the target.
  • Figure 4b response is only an example of the calibration results, an ideal compensation would result in a fixed frequency of perfectly uniform amplitude across the entire sweep of the chirp.
  • the frequency of the Figure 4b I channel results 450 would ideally be fixed corresponding to the difference in frequency between the transmit wavefront and the receive wavefront as received at the mixer in the receiver chain.
  • the Figure 4b response should also have perfectly uniform amplitude because there should be no difference in attenuation of the calibrated system over the full frequency sweep within the chirp.
  • the empirical results shown in Figure 4b of the gain compensation mechanism are a dramatic and valuable improvement in gain flatness over the uncompensated response of Figure 4a.
  • FIG. 5 is a flow diagram of an example method of generating gain compensation values for the present invention. Initially, an ultra- wideband system is built and a flat stationary target is placed in front of the transmit and receive antenna element array. The gain compensation table or gains compensation values are set to a constant level (step 505). The transmitter is swept across the multiple gigahertz bandwidth (step 510). The transmitter is swept using a first transmit and receiver element pair.
  • in-phase (I ) and quadrature phase (Q) responses are sampled and recorded (step 515).
  • 128 samples across the bandwidth are measured for each chirp or frequency sweep of the system.
  • steps 510 and 515 are repeated after selecting a next transmit and receive antenna element pair until all transmit and receive element pairs have been exercised.
  • 192 elements pairs are sampled. If all elements have been exercised, then the average amplitude value at each frequency point is calculated for all elements (step 525).
  • the I and Q channel sample values are each squared and added to determine the effective power of the detected reflection signal.
  • the average value for each frequency point is then inverted to compute the rough gain compensation value (step 530).
  • the rough gain compensation values are normalized to produce a uniform set of gain compensation values (step 535).
  • the normalized gain values are then scaled to fit the D/ A converter dynamic range (step 540). In one embodiment, the dynamic range may be 8 bits.
  • the normalized and scaled gain values may then be loaded into the gain compensation tables (step 545).
  • the ultra-wideband transceiver can now operate in a gain compensated mode. As a result, the I , Q, or power combination of both channels appears to be substantially uniform over the frequency range of the sweep or chirp.
  • FIG. 6 is a flow diagram showing a method 600 having aspects of the current invention.
  • the method 600 controls an ultra-wideband system for the measurement of an individual using a gain compensated ultra-wideband frequency transmission scheme. Initially, a first transmit and receive antenna array having a plurality of element pairs is selected (step 605). A sweep of a gain compensated ultra- wideband frequency band is initiated (step 610). Simultaneous with the sweep, a reflected signal of the gain compensated ultra- wideband frequency band signal is received and downconverted (step 615). The do wncon verted signal is demodulated (step 620). [0031] The process may end (step 625) if only one sweep of the system is needed.
  • some systems will require multiple sweeps and post processing of the results. For example, if a sweep of each antenna element receive and transmit pair is desired, then the process determines if all of the antenna elements have been sampled (step 630). If not, then steps 605-620 are repeated for the next antenna element pair. If all antenna elements have been sampled, then post-processing of the gain compensated demodulated data may be accomplished (step 635). This post processing includes extracting measurements of an individuals body from the demodulated data.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Radar Systems Or Details Thereof (AREA)
  • Transceivers (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

Abstract

Un circuit conçu pour fournir une compensation de gain à une réponse de fréquence balayée dans un système à ultralarge bande consiste à utiliser un signal de FI d'amplitude variable dans un mélangeur gigahertz pour commander l'amplitude d'un émetteur-récepteur à ultralarge bande. Le signal de FI d'amplitude variable est généré par un multiplicateur recevant un signal de fréquence intermédiaire IF à un niveau fixe et une entrée de commande de gain. L'entrée de commande de gain étant fournie par un convertisseur numérique-analogique commandé par des valeurs de commande de gain d'une table de conversion. Les valeurs de la table de conversion sont générées par inversion, normalisation et mise à l'échelle de la réponse de gain non compensée du système à ultralarge bande. Le système à compensation de gain porduit une réponse d'amplitude sensiblement plate au niveau de la sortie d'un récepteur en quadrature.
PCT/US2006/060982 2006-11-16 2006-11-16 Compensation de gain dans un émetteur-récepteur à ultralarge bande Ceased WO2008060298A2 (fr)

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PCT/US2006/060982 WO2008060298A2 (fr) 2006-11-16 2006-11-16 Compensation de gain dans un émetteur-récepteur à ultralarge bande

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PCT/US2006/060982 WO2008060298A2 (fr) 2006-11-16 2006-11-16 Compensation de gain dans un émetteur-récepteur à ultralarge bande

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WO2008060298A2 true WO2008060298A2 (fr) 2008-05-22
WO2008060298A3 WO2008060298A3 (fr) 2008-09-12

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114362842A (zh) * 2021-12-21 2022-04-15 中电科思仪科技(安徽)有限公司 一种适用于5g高频段大带宽多通道信道探测装置及方法

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU2003295479A1 (en) * 2002-11-15 2004-06-15 Time Domain Corporation A system and method for processing signals in uwb communications
EP1789808A1 (fr) * 2004-07-30 2007-05-30 Picosecond Pulse Labs Echantillonneurs de guide d'onde et convertisseurs de frequence

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114362842A (zh) * 2021-12-21 2022-04-15 中电科思仪科技(安徽)有限公司 一种适用于5g高频段大带宽多通道信道探测装置及方法
CN114362842B (zh) * 2021-12-21 2024-04-19 中电科思仪科技(安徽)有限公司 一种适用于5g高频段大带宽多通道信道探测装置及方法

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