Digital Filter Package 2 (DFP2) Software Instruction Manual
Digital Filter Package 2 Software Instruction Manual © 2013 Teledyne LeCroy, Inc. All rights reserved. Unauthorized duplication of Teledyne LeCroy documentation materials other than for internal sales and distribution purposes is strictly prohibited. However, clients are encouraged to distribute and duplicate Teledyne LeCroy documentation for their own internal educational purposes. Digital Filter Package 2 and Teledyne LeCroy are registered trademarks of Teledyne LeCroy, Inc.
DFP2 Option INTRODUCTION...................................................................................................3 The Need.......................................................................................................................................... 3 The Solution ..................................................................................................................................... 3 Enhanced Solutions .....................................................................
BLANK PAGE 2 ISSUED: June 2013 923134 Rev A
DFP2 Option INTRODUCTION The Need In today's complex environment, data is frequently composed of a mixture of analog and digital components spread over a broad range of frequencies. In many applications, the relevant data is encoded or obscured. Capturing the right signals becomes a challenge. Engineers find it increasingly difficulty to examine only those parts of the data they are interested in. Traditional (or even smart) oscilloscope triggering cannot always provide a satisfactory answer.
design or with a math package such as MATLAB or Mathcad. Filter coefficients can be directly downloaded from the program into the scope, using the DSOFilter utility. It is also possible to specify the filter coefficients on an Excel spreadsheet and to use DSOFilter to download them from the spreadsheet to the scope. DFP2's flexibility is shown by the following example: 1. A 25 kHz square wave combined with an unwanted 60 Hz sinusoidal component. 2.
DFP2 Option Kinds of Filters1 Low-pass Filter Low-pass filters are useful for eliminating accumulated high-frequency noise and interference, and for canceling high-frequency background noise. Sample applications are in datacom, telecommunications, and disk drive and optical recording analysis for accurate RF signal detection. Band 1: Pass Band — DC to top of the transition region; signal passes unattenuated. Band 2: Transition Region — edge frequency to edge frequency plus width; increasing attenuation.
Band-pass Filter Band-pass filters are useful for emphasizing a selected frequency band. Sample applications include radio channel identification, broadband transmission, ADSL, clock generators (i.e., eliminating the central frequency and displaying harmonics only), and telecommunications (Jitter measurement over a selected frequency range). Band 1: First Stop Band — DC to bottom of first transition region; highly attenuated.
DFP2 Option Communications Channel Filters Raised Cosine (a low-pass filter) These filters belong to the low-pass filter category (with a variety of shapes). Raised cosine is one of a class of filters used to minimize intersymbol interference: the time domain impulse response crosses zero at all bit time intervals except the one with the impulse. Applying raised root cosine twice (or at the sending and receiving end of a signal, for example) results in a raised cosine filter effect.
Raised Root Cosine (a low-pass filter) Band 1: Pass Band — DC to corner frequency minus half width; signal passes unattenuated. Band 2: Transition Region — corner minus half width to corner plus half width; attenuation increases with frequency with a rolloff shape of 0.5[cos(a) + 0.5]½, where a ranges from 0 to p over the transition region. This region is determined by b, which is specified as a percentage of the corner frequency.
DFP2 Option IIR Filters Infinite Impulse Response (IIR) filters are digital filters that emulate analog filters. The four types offered by the DFP2 option are as follows: • Butterworth • Chebyshev • Inverse Chebyshev • Bessel The Butterworth or "maximally flat" filter has the flattest amplitude response of all the available filters. The Bessel filter is noted for its uniform phase response as a function of frequency. The following figure shows a comparison between Butterworth and Bessel filters.
In the setup of these filters, you have control of cutoff frequencies, transition region width, and stop band attenuation. FILTER SETUP To Set Up a DFP Filter 1. Touch Math in the menu bar then Math Setup... in the drop-down menu. 2. Touch the Fx tab (F1 your filtered waveform. for example) for the math trace you want to display 3.
DFP2 Option 9. Touch the Frequencies tab. 10. Depending on the class (FIR/IIR) and kind of filter you selected, and whether or not Auto Length is enabled, you can change the cutoff frequencies, transition width (edge width), stop band attenuation, and pass band ripple. MULTIRATE FILTERS Description In many of today's development environments, digital filter design has become most challenging.
1. A noisy sine wave with a frequency of 3 MHz. 2. The first low-pass filter with 20 MHz edge frequency and 30 MHz transition region is applied. 3. A sparsed version of trace A. 4. A second low-pass filter with an edge frequency of 5 MHz and a transition region width of 6 MHz is applied to the sparsed trace in 3. The last trace shows the zoomed signal, which was filtered by a multistage filtering method. Notice that all high frequency noise components were removed.
DFP2 Option CUSTOM FILTERS Custom Filter Setup If the standard filters provided with DFP2 are not sufficient for your needs, you can create filters with virtually any characteristic, up to 2000 taps. The required custom filter can be designed with a digital filter design or math package such as MATLAB or Mathcad. The filter coefficients can then be loaded into the scope from an ASCII file. The file consists of numbers separated by spaces, tabs, or carriage returns. Note: Do not use commas as separators.
Now create an ASCII file containing the coefficients: FirFilter.
DFP2 Option Writing Data to a Data File To write values from Mathcad version 11 to a data file, you can use the File Read/Write component, as follows: 1. Click in the blank spot in your worksheet. 2. Choose Insert, Data, File Output from the menu.
3. This opens the File Options wizard: 4. From the File Format drop-down list choose "Tab Delimited Text". 5. Press Finish. The File Output component icon will appear in your spreadsheet, with the path to the data file under it. Underneath that, the cursor is on a placeholder for the name of the Mathcad variable containing the data to be written to the data file. Enter the name of the variable.
DFP2 Option Example 2: Creating an IIR Filter Coefficient File Using Mathcad Note: This example uses the Mathcad Signal Processing Extension Pack. order := 6 fcutoff := .1 A := iirlow( butter ( order ) , fcutoff ) ⎛ 0.083 1 0.067 1 0.061 1 ⎞ A = ⎜ 0.166 −1.404 0.135 −1.143 0.122 −1.032 ⎜ ⎝ 0.083 0.736 0.067 0.413 0.061 0.276 ⎠ x := 0 , .001.. .5 1 gain( A , x) 1 0.5 0 0 0 0 0.1 0.2 0.3 x 0.4 0.5 0.5 Now create an ASCII file containing the coefficients: IirFilter.
Note: In the example above, because “A” has a predefined meaning (as a unit) in Mathcad 11, it appears with a green underline. However, earlier versions of Mathcad give no warning about using "A" as a variable name, and it may still be used for this purpose. What gets written to lirfilter.txt is as follows: 0.0828825751812225 1 0.0674552738890719 1 0.0609096342883086 1 0.165765150362445 -1.40438489047158 0.134910547778144 -1.1429805025399 0.121819268576617 -1.03206940531971 0.0828825751812225 0.
DFP2 Option Writing Data to a Data File To write values from Mathcad to a data file, you can use the File Read/Write component, as follows: 1. Click in the blank spot in your worksheet. 2. Choose Component from the Insert menu. 3. Select File Read or Write from the list and click Next. This launches the first part of the File Read or Write Setup Wizard. 4.
