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| Demo of the GUI |
Today is a big day to all Chinese in the world, the Lunar
Chinese New Year, and I’d like to wish all a lucky, happy, healthy and wealthy year of
horse ahead!
It’s a time for many Chinese to party and eat to the heart’s content with
good excuses to avoid feeling guilty and at the same time make the resolution
for the whole new year. More than often, we tend to wait for a
“proper” time for the real action to follow for reasons such as “busy to clear
things on hand first”, “need to wait for a good chunk of time” and in the end, the chances are "the right time" never comes. But sometimes, if we chose to “slot it in” and “start it
now”, we could be amazed at how easy it can be done (relative to what we had thought) and how much we can achieve with small steps a time. The excel sheet to be described can do a lot of things for an engineer who are interested in phase noise and/or
jitter measurement. More importantly, the concept can be extended and applied
to integrate test and measurement automation with automatic report generation
(data post processing and visualization) in Excel. However, it get started only as
a simple worksheet to calculate the RMS RJ value from the user supplied phase noise
data which took less than 5 minutes to create. It is then fairly easily expanded into what it is now with the capabilities to:
- Take in phase noise in “frequency-phase noise”
data pairs and calculate the RMS RJ value. This is the spectrum analyzer based
clock source random jitter measurement method described in FC-MJSQ and can be used
to study the characteristics of different kinds of clock sources.
- Pass the phase noise data through PLL and
calculate the PLL filtered RMS RJ value. It can be used to study the PLL
characteristics and its jitter shaping effect on clock sources.
- Pass the phase noise data through PLL first and
then a golden PLL. It can be used for transmitter compliance test.
- One-button click to perform phase noise
measurement from the clock source directly if spectrum analyzer is connected to
the host PC through GPIB. This will automate the phase noise raw data acquisition into the Excel
instead of manually cut/paste.
- One-button click to perform screen capture of
the spectrum analyzer for documentation and reporting purposes.
Here
is the step-by-step guide on how to make this Excel sheet:
To achieve capability 1:
Cut/paste
or import from text-based files such as “*.txt” or “*.csv” for the raw phase
noise data into the Excel sheet column A and B and key in the trapezoidal integration
equation in column C (start from C3) as shown in Figure 2. You can drag the
equation that is filled into C3 all the way down to fill in the column C with
the same equation.
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| Figure 2: trapezoidal integration equation |
The summation of column C is the SSB noise power and the RMS
phase noise Phi (in unit of radius) is the square root of twice the SSB power, in
Excel, Phi = SQRT(2*SUM(C:C)).
To achieve capability 2:
You can calculate the transfer function of your PLL and put
the data into column D in dB, the phase noise output through the PLL is simply
the addition of raw phase noise and the PLL transfer function in dB and is
presented in column E as shown in Figure 3. As an example, the second order PLL
transfer function for PCIe described in [1] is used with a 3dB loop bandwidth
of 15MHz and a damping factor of 0.54.
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| Figure 3: TX PLL transfer function |
The trapezoidal integration equation is used in column F to
calculate the SSB noise power after the raw data goes through the PCIe PLL.
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| Figure 4: SSB noise power at the TX PLL output |
To achieve capability 3:
Use the same method and integration equation as before to
implement the first type golden PLL defined in [2]. The completed input is
shown in Figure 5 as below.
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| Figure 5: first type golden PLL transfer function |
The SSB noise power for the raw phase noise, the output from
(TX) PLL and the output from the golden PLL are calculated and presented in K2
to M2 as shown in Figure 6.
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| Figure 6: SSB noise power calculation |
To make the phase noise/jitter results more presentable, a
new sheet is used as GUI with the layout shown in Figure 7, where the phase
jitter in second is dependent on the carrier frequency.
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| Figure 7: calculated phase noise output |
At this point, you can also plot all the transfer functions
as shown in Figure 8 and the phase noise as shown in Figure 9.
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| Figure 8: transfer function plots |
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| Figure 9: phase noise plots |
To achieve capability 4:
Of course, I certainly don’t want to hard code the GPIB port
and address for the spectrum analyzer. Thus, the input
interface as in Figure 10 is provided. Instead of using the cell values
directly, the named ranges are used so that when the “GUI” is reformatted,
there is no need to change the codes because of the shifting of the cell
positions.
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| Figure 10: named ranges for GPIB interface information |
Put a command button onto the Excel sheet and “assign
Macros” Button1_Click() as shown below will automate the phase noise data
downloading into the Excel.
Sub
Button1_Click()
Dim ioMgr As
VisaComLib.ResourceManager
Dim instrument As
VisaComLib.FormattedIO488
Dim idn As String
Dim lpl() As String
Dim freq() As Double
Dim dBc() As Double
Dim rowStart As Integer
Dim iLastRow As Long
Dim lpln As Integer
Set ioMgr = New
VisaComLib.ResourceManager
Set instrument = New
VisaComLib.FormattedIO488
Set instrument.IO =
ioMgr.Open(Sheets("MainGUI").Range("gpib_port").Value &
"::" & Sheets("MainGUI").Range("gpib_addr").Value)
‘ this is the same as below line
'Set instrument.IO =
ioMgr.Open("GPIB0::03")
instrument.IO.Timeout = 10000
lpln =
CInt(Sheets("MainGUI").Range("C11").Value) ‘ provide the
option to chose the trace
instrument.WriteString
":FETC:LPL" & lpln & "?"
lpl =
instrument.ReadList(VisaComLib.IEEEASCIIType.ASCIIType_BSTR, ",")
instrument.IO.Timeout = 5000
rowStart = 2
For i = (LBound(lpl)) To
(UBound(lpl) - 1) Step 2
ReDim Preserve freq(0 To
i / 2)
ReDim Preserve dBc(0 To i
/ 2)
freq(i / 2) = lpl(i)
dBc(i / 2) = lpl(i + 1)
Next i
Sheets("LPLData").Range("A" & rowStart &
":A" & (UBound(dBc) + rowStart)).Value =
Application.Transpose(freq)
Sheets("LPLData").Range("B" & rowStart &
":B" & (UBound(dBc) + rowStart)).Value =
Application.Transpose(dBc)
'clear the old f-PN contents
rowStart = UBound(dBc) +
rowStart + 1
iLastRow =
Sheets("LPLData").Cells(Rows.Count, "a").End(xlUp).Row
Sheets("LPLData").Range("A" & rowStart &
":" & "Z" & iLastRow).Clear
Call TFCalc ‘ calculate the transfer function
Call updatePlots ‘ update the plots
End Sub
To achieve capability 5:
It’s just one more command button with a little bit more
coding. You can look into the codes under Button2_Click() if you are interested.
Of course, it’s handy to add in some more features such as
the start/stop frequency so that you have the option to change the frequency span for
the phase noise measurement. The option to choose which trace to download: raw
data trace or the smoothed data trace. And the flexibility of changing the 3dB
cut off frequency of the golden PLL.
By now, we are almost done. As all the raw data are
organized into one sheet named “LPLData” and the input/output GUI into another sheet
named “MainGUI”, automatically download the phase noise raw data doesn’t pose
any issue as it has been taken care of by the Macros. However, manually
cut/paste the data from external sources into the Excel sheet may risk
overwriting the equations inside the cells, thus corrupting the excel sheet. To avoid this situation, instead of input the equations manually into the Excel sheet, the transfer
function calculation and the trapezoidal integration equations have been
packed into Macros, making this process fully automated. In addition, an extra
Excel sheet named as “PNData” is used for external phase noise data manual
input as shown in Figure 12.
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| Figure 12: phase noise manual input interface |
A typical procedure for manually input the phase noise data
is outlined in the following:
- Navigate to sheet “PNData”, click on “Delete PN
Data” to clear old data points.
- Copy the external data and paste them into column A
and B from row 2 onwards.
- Navigate to sheet “MainGUI” and click “Manual PN
Data”. All the calculations will be done
automatically with results updated instantly.
The
sample code used for PCIe PLL transfer function calculation is given as below:
Function
HdB(f3db As Double, zeta As Double, f) As Double
Dim i As Integer
Dim n As Double
Dim d As Double
Dim w As Double
Dim w2 As Double
Dim wn As Double
Dim H As Double
w = 2 *
Application.WorksheetFunction.Pi() * f 'omega
w3 = 2 *
Application.WorksheetFunction.Pi() * f3db
'omega 2
wn = w3 / Sqr(1 + 2 * zeta ^
2 + Sqr((1 + 2 * zeta ^ 2) ^ 2 + 1)) 'omega n
n = wn * Sqr(wn ^ 2 + 4 * w ^
2 * zeta ^ 2) 'numorator
d = Sqr((wn ^ 2 - w ^ 2) ^ 2
+ (2 * w * wn * zeta) ^ 2) 'denominator
H = 20 *
Application.WorksheetFunction.Log10(n / d)
HdB = H
End Function
The finished GUI is shown in Figure 13.
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| Figure 13: finished GUI |
References:
1. PCI ExpressTM Jitter Modeling Revision 1.0RD
2. Fiber Channel - Methodologies for Jitter and Signal Quality Specification - MJSQ
