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MixIMT_Data (Multi-RF Intermodulation Table Mixer Data Model)

Symbol

Available in ADS

Parameters
Name Description Units Default
Filename Name of IMT file to be read "imtfile.imt"
RFharms[r] Number of harmonics of r-th RF input involved in mixing None 1, r=1
RFfreq[r] Fundamental frequency of r-th RF tone Hz 1.1 GHz, r=1
LOharms Number of LO harmonics involved in mixing None 2
LOfreq Fundamental frequency of LO tone Hz 1.0 GHz
ZRF Impedance of RF port Ohm polar(50,0)
ZIF Impedance of IF port Ohm polar(50,0)
ZLO Impedance of LO port Ohm polar(50,0)
ConvGain Voltage conversion gain from RF to IF port None dbpolar(0,0)
RFreflection †† Wave variable reflection at RF port (S11) None polar(0,0)
IFtoRFleakage †† Wave variable leakage from IF to RF port (S12) None polar(0,0)
LOtoRFleakage †† Wave variable leakage from LO to RF port (S13) None polar(0,0)
RFtoIFleakage †† Wave variable leakage from RF to IF port (S21) None polar(0,0)
IFreflection †† Wave variable reflection at IF port (S22) None polar(0,0)
LOtoIFleakage †† Wave variable leakage from LO to IF port (S23) None polar(0,0)
RFtoLOleakage †† Wave variable leakage from RF to LO port (S31) None polar(0,0)
IFtoLOleakage †† Wave variable leakage from IF to LO port (S32) None polar(0,0)
LOreflection †† Wave variable reflection at LO port (S33) None polar(0,0)
Add or remove elements of repeated parameters from dialog box. Ensure that identical number of harmonics and frequencies are specified at all times. †† Reflection and leakage parameters apply to entire spectra present at relevant ports, although RF and LO ports are internally frequency sensitive. See note 6.

Notes/Equations
  1. MixIMT_Data is a behavioral mixer component that relies on IMT files. When supplied with an IMT file in O, A or B formats, it emulates mixer behavior by sensing power levels at specified frequencies on the RF and LO ports and reproducing the IF spectrum described in the data file at the output port. Based on the use of the RFfreq[] parameter, it is capable of sensing multiple unrelated fundamental tones at the RF input and generating intermodulation products as specified by multi-tone spurs on file. It senses only the LOfreq tone at the LO input and uses it for determining mixing products.
  2. The basic behavior described above can be further modified by specifying non-default voltage conversion gain and port leakage/reflection values. See Working with Data Files > IMT Format for more information.
  3. MixIMT_Data operates on each type of IMT file as follows:
    When supplied with an O-type (single-RF, single side banded data with no phase information) file, it generates identical upper and lower side band behavior for any mixing product. When supplying this type of IMT file, the user should ensure that the instance is made sensitive to only the one RF tone of interest. Note that these IMT files do not contain any frequency information. Thus the spur behavior described on file can be reproduced at any RFfreq and LOfreq of interest.
    When supplied with an A-type (single-RF, double side banded data with phase information) file, it generates distinct upper and lower side band behaviors as recorded on file. When supplying this type of IMT file, the user should ensure that the instance is made sensitive to only the one RF tone of interest. Since A-type IMT files contain actual values of frequencies and powers, if the RFfreq[1] or LOfreq specified on the behavioral instance does not match the file values, then frequency and power domain interpolation is done to predict a mathematically supportable behavior.
    When supplied with a B-type (multi-RF, double side banded data with phase information) file, it generates distinct upper and lower side band behaviors as recorded on file. When supplying this type of IMT file, the user should ensure that the instance is made sensitive to as many RF tones as are present on file. Since B-type IMT files contain actual values of RF frequencies, deviation of the RFfreq[r] from the behavioral instance of file values is not tolerated. Deviation of sensed RF power is allowed. Deviations of LO frequency/power and RF power at established frequencies are responded to by frequency and power domain interpolation as explained in Working with Data Files > IMT Format.
  4. IMT matrices up to [( 2* RFharms[1] + 1 )*..... *( 2* RFharms[r] + 1 )] x ( LOharms + 1) can be supported by this data model if a table is available on file. Although there is no theoretical upper limit on the number of harmonic indices that can be specified on the data model, the user should establish a cut-off on the number of IF spurs to improve the performance of the underlying harmonic balance simulation. Using the equation for matrix size defined above, it can be verified that a simple three-tone RF input, such as used for adjacent channel power rejection (ACPR) tests, mixed at RFharm[] = {3,2,2} with LOharm = 5 will generate a 175 x 5 IMT matrix. Lowering the spur precision by 1 on each RF tone will produce a more manageable 45 x 5 IMT matrix.
  5. To understand the use model for this data model see example designs: BehavioralModels > MixIMT_prj > BEH_IMT_*.dsn. Also see related extraction components MixIMTA_Setup (Single-RF Intermodulation Table Extractor) and MixIMTB_Setup (Multi-RF Intermodulation Table Extractor).
  6. The internal topology of MixIMT_Data is dynamically generated during simulation. It is possible to trade off the number of spurs generated by the model against simulation performance. Compare resource consumption of example designs BEH_IMT_1R2R_2L.dsn and BEH_IMT_1R1R_2L.dsn from the example project in Note #5. Both designs contain behavioral mixers which read the same data file. However, in the second case the desired degree of distortion is reduced on the second RF tone, resulting in faster simulation without sacrificing accuracy of any desired intermodulation product.
  7. The MixIMT_Data model is based on an FDD which responds to exact frequencies of interest supplied on the model instance. When designing a mixer where colliding tones exist at the output spectrum, offset the frequency of one of the input tones by a negligible amount to ensure proper simulation. For example when signal frequency is RFfreq[1] = 2.0 GHz and image frequency is RFfreq[2] = 1.4 GHz, with LOfreq = 1.7 GHz, colliding tones are expected at the difference frequency of 300 MHz. Set RFfreq[2] = 1.4 GHz + 1e-3 Hz on the data model, the source, as well as the simulator if applicable. See design BEH_IMT_1R2R_2L.dsn in example project BehavioralModels > MixIMT_prj.
  8. Applying conversion gain to a system level IMT mixer model is a means of altering the part of the IF spectrum at the IF port that is influenced by RF signal power, without affecting other tones or any other signals at any other ports. Given signal magnitude (in dBm) of RFdBm and phase RFdeg at the RF input, a conversion gain of value dbpolar (CGdB, CGdg) ensures that the internal RF magnitude (in dBm) is altered to RFdBm + CGdB and internal RF phase to RFdeg + CGdg prior to the mixing process without any impact on the external RF pin. The internal RF magnitude (in dBm) and phase is then used to generate the IF spectrum after appropriate scaling with respect to nominal RF power in the IM table. See design BEH_IMT_2R_4L_ConvGain.dsn in example project BehavioralModels > MixIMT_prj.

    QRF = PRF + dbpolar(CGdb,CGdeg)
    Estimation of the change in the IF spur at nLO X mRF due to the supplied signal and conversion gain is computed as ΔPIF such that:
    dB(ΔPIF {nLO,mRF}) = |mRF| * (PRF + CGdb-PRFnom) + |nLO| * (PLO - PLOnom)
    phase(ΔPIF {nLO,mRF}) = mRF * (CGdeg)

    Note If there are phase shifts in signals applied at external RF or LO ports, they will impact the phase of the IF spurs in addition to the shifts introduced by the conversion gain parameter.

  9. MixIMT_Data accepts all IMT values as representative of absolute magnitude (in dBm) (and phases when applicable) of IF spurs. Therefore, when trying to replace a MixerIMT2 model which was in use in the relative magnitude (in dBm) or dB mode, the corresponding IMT table should be manually converted into a DBM style table. The simplest way to achieve this is to manually edit all IF spurs by adding the amount of the baseline magnitude (in dBm). There are two conventions for baseline power: one being the value of RF signal magnitude (in dBm) at RF input and the other being an expected IF fundamental magnitude (in dBm) at IF port. To address the former convention, the RF signal value is always included in an IMT file and could be applied as an additive to all spurs. If the latter convention is desired, then the absolute value of IF fundamental should be determined and applied to the Mix(1,1) data point in the table. All other spurs will need to be upgraded by the same amount.
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