Mixer Spur Chart v.2 - Calculator Help

Contents

8-Minute Demo/Tutorial (Highly Recommended)

Quick Tips

General Information
Setting up the Simulator

Interpreting Output

Upconversion
Advanced Settings

Quick Tips

General Information
This program is a mixer spur chart calculator/simulator. It predicts both frequency and power levels of spurious products. The user operates this program be entering in the desired values for mixer operation and clicking the calculate button. Information about spurs can be obtained by clicking on any line in the graph that is plotted when the calculate button is clicked. This program was written in Java. Comments and questions regarding operation of the simulator can be directed to spurchart@hittite.com. This program is provided as is, with no guarantee of support, but we will make an effort to answer questions when possible. For information regarding Hittite Microwave Corporation's line of mixers or other GaAs ICs, please e-mail us at sales@hittite.com.

Setting Up The Simulator

Upconversion/Downconversion
Upconverting operation usually entails a signal being injected into the mixer on the IF port and a higher frequency signal leaving the mixer on the RF port. This simulator automatically selects the correct input and output values depending on which of the Conversion Option Boxes (on the Basic Tab) is depressed.  The conversion mode should be the first selection, because certain other inputs (such as the boxes representing input power levels) may not apply in different modes.  Also, this simulator has no restriction on the RF frequencies being higher than the IF frequencies, therefore allowing users to display a large band of information at the same time.

Frequency Input
The first thing the user must do when running this program is enter the frequency values for the desired mixer operation. In this version, the LO input frequency can be fixed or swept, and one can sweep over a specified RF input band, and observe spurs that come out of a specified IF output band. The RF band is specified by setting the starting value RF Low, as well as the highest value to sweep to, RF High. The user can also specify the frequency area of interest by bounding that range on the low end with RF Spec1 and on the high end with RF Spec2. In this way, the user tells the simulator what frequencies are actually of interest in the calculation. The same limits apply to the IF output  To activate the swept LO feature switch to the Swept LO tab.  Here, one can activate the Swept LO by pushing the red button.  They can input in the Minimum and Maximum LO during the sweep, as well as enter  in a nominal frequency.  This nominal frequency will be displayed as a marker between the Min and Max LO.  When the simulator plots output, it draws a green rectangle inside of the graph, or, if in Swept LO mode, displays three rectangles representing the Minimum, Maximum and Nominal LOs.  Any lines that intersect this rectangle are spurs that fall within the frequency range of interest, specified by the values RF Spec1, RF Spec 2, IF Spec1, and IF Spec2.  Similarly, any spurs that fall within the area connecting the Min. LO and Max. LO boxes are in the frequency range of interest for a Swept LO.  The units for all frequency values are in gigahertz (GHz). All frequency values must be positive values. For the RF and IF sweep ranges, the sweep must continually increase in frequency, i.e. RF(IF) Low <= RF(IF) Spec1 <="RF(IF)" Spec2 <="RF(IF)" High.  The LO Sweep must also increase continually, i.e. Minimum LO <= Nominal LO <= Maximum LO.

N and M values
The user must also specify maximum values for N and M, the factors by which the LO and RF/IF frequencies are multiplied by in calculating the intermodulation suppression frequencies. M is the factor for the input (RF/IF) frequency, and N is the factor for the LO frequency. The simulator will calculate all spurs for which the LO harmonic factor is between -N to N, and the RF harmonic factor is between -M to M. These values must be positive integers. These predicted results are reasonably accurate for n less than or equal to eight and m less than or equal to four.

Power Input
The user can specify power levels for both the RF and IF signals. The data is used in calculating the suppression of the output spurs. All power level input is in dBm. Values can be positive or negative, but the RF power level must be at least 5 dBm below the LO power level.

Interpreting Output

Plot
Once all the data has been entered, the user can click the Calculate button to plot mixer output on the graph. The input frequency will be on the x-axis, and the output frequency will be on the y-axis. The green rectangle in the graph corresponds to the frequencies between the Spec1 and Spec2 settings at the Fixed/Nominal LO specified while setting up the simulator. The user can click on any line on the graph to view more information about the particular spur that that line represents.  This information is displayed in the table and on the Spur Info tab.  All the spurs are color coded (see key above in Quick Tips).

Table/Spur Info Pane
This window shows the order of the spur, in n by m terms, its suppression in dBc, and whether or not it falls in the frequency of interest range.  When sweeping the LO, information on the lowest and highest frequencies of LO, RF, and IF in which the spur lies within the box is also displayed.  Power level, however, is not a function of input frequency, and remains constant as the user clicks on different portions of the spur line.  By clicking a particular spur in the table, the spur will be highlighted in the chart.  The table can sort information by a particular column by clicking on the table header.  Clicking it again will sort in the opposite order.  Columns can also be rearranged by dragging the column headers left or right and can be resized by dragging the area between columns.  The position of the table can be changed by going to the Advanced tab and clicking the Divider button.

Advanced Settings
Power level calculations rely on certain constants which attempt to approximate behavior of the mixer that vary from mixer design to mixer design. To edit this constants to better model a particular mixer, one can click on the Advanced tab.  To reset all the constants to defaults, push the Default button.  To switch the location of the table, click the Divider button.  Descriptions of all the constants:

Delta Variables
In a real mixer each of the four diodes has
slightly different voltages caused by impedance
variations between the diodes. This simulator
approximates those differences by normalizing the
voltage of each of the diodes with respect to
the voltage of diode #1. This factor is
approximated for diodes 2-4 in the variables
delta 2-4, respectively. In an ideal mixer
delta2 = delta3 = delta4 = 1.

 Alpha and Beta
These variables are the measures of the L and R
port imbalance. Alpha is the ratio of the
voltage-to-ground at both locations where the
L port balun ties to the diodes. Beta is the
same for the R port balun. Ideally, both alpha
and beta are 1.

 VF
This variable is the diode forward voltage for
a current of 1 mA. This can be lowered for
a Low Barrier diode and raised for a High Barrier
diode.

HiPwr Thresh
This variable is used to determine which spurs should be considered
high power (and colored accordingly).  All spurs above this
number will be colored as high power.

Cutoff Thresh
This variable is used to determine which spurs should be considered
superfluous.  All spurs below this number will not be displayed
in the plot or table.