Markus Nentwig Blog on DSPRelated.com https://www.dsprelated.com/blogs-1/nf/Markus_Nentwig.php Markus Nentwig Blog on DSPRelated.com https://www.dsprelated.com/blogs-1/nf/Markus_Nentwig.php https://d23s79tivgl8me.cloudfront.net/user/profilepictures/24789.jpg en-US Sun, 14 Jun 2026 13:51:43 +0000 1781445103 A poor man's Simulink https://www.dsprelated.com/showarticle/707.php Glue between Octave and NGSPICE for discrete- and continuous time cosimulation (download) Keywords: Octave, SPICE, Simulink

Introduction

Many DSP problems have close ties with the analog world. For example, a switched-mode audio power amplifier uses a digital control loop to open and close power transistors driving an analog filter. There are commercial tools for digital-analog cosimulation:...]]> Sat, 24 Jan 2015 10:41:34 +0000 Markus Nentwig Spline interpolation https://www.dsprelated.com/showarticle/594.php A cookbook recipe for segmented y=f(x) 3rd-order polynomial interpolation based on arbitrary input data. Includes Octave/Matlab design script and Verilog implementation example. Keywords: Spline, interpolation, function modeling, fixed point approximation, data fitting, Matlab, RTL, Verilog

Introduction

Splines describe a smooth function with a small number of parameters. They are...]]> Sun, 11 May 2014 10:47:57 +0000 Markus Nentwig Signed serial-/parallel multiplication https://www.dsprelated.com/showarticle/555.php Keywords: Binary signed multiplication implementation, RTL, Verilog, algorithm

Summary
  • A detailed discussion of bit-level trickstery in signed-signed multiplication
  • Algorithm based on Wikipedia example
  • Includes a Verilog implementation with parametrized bit width
Signed serial-/parallel multiplication

A straightforward method to multiply two binary numbers is to repeatedly shift...]]> Sun, 16 Feb 2014 14:37:19 +0000 Markus Nentwig Shared-multiplier polyphase FIR filter https://www.dsprelated.com/showarticle/198.php Keywords: FPGA, interpolating decimating FIR filter, sample rate conversion, shared multiplexed pipelined multiplier

Discussion, working code (parametrized Verilog) and Matlab reference design for a FIR polyphase resampler with arbitrary interpolation and decimation ratio, mapped to one multiplier and RAM.

Introduction

A polyphase filter can be as straightforward as multirate DSP ever gets,...]]> Wed, 31 Jul 2013 09:31:00 +0000 Markus Nentwig Noise shaping https://www.dsprelated.com/showarticle/184.php eywords: Quantization noise; noise shaping

A brief introduction to noise shaping, with firm resolve not to miss the forest for the trees. We may still stumble over some assorted roots. Matlab example code is included.

Quantization

Fig. 1 shows a digital signal that is reduced to a lower bit width, for example a 16 bit signal being sent to a 12 bit digital-to-analog converter. Rounding to...]]> Sun, 09 Dec 2012 15:56:03 +0000 Markus Nentwig 'z' as in 'Zorro': Frequency Masking FIR https://www.dsprelated.com/showarticle/180.php An efficient way to implement FIR filters. Matlab / Octave example included. Keywords: Frequency masking FIR filter implementation

Introduction

An "upsampled" FIR filter uses multiple-sample delays between the taps, compared to the unity delays in a conventional FIR filter. The resulting frequency response has steeper edges, but contains periodic images along the frequency axis (Fig. 1). ...]]> Tue, 02 Oct 2012 15:39:03 +0000 Markus Nentwig FIR sideways (interpolator polyphase decomposition) https://www.dsprelated.com/showarticle/178.php An efficient implementation of a symmetric-FIR polyphase 1:3 interpolator that doesn't follow the usual tapped delay line-paradigm. The example exploits the impulse response symmetry and avoids four multiplications out of 10. keywords: symmetric polyphase FIR filter implementation ASIC Matlab / Octave implementation

Introduction

An interpolating FIR filter can be implemented with a...]]> Wed, 12 Sep 2012 20:20:17 +0000 Markus Nentwig Design of an anti-aliasing filter for a DAC https://www.dsprelated.com/showarticle/177.php

  • Octaveforge / Matlab design script. Download: here
  • weighted numerical optimization of Laplace-domain transfer function
  • linear-phase design, optimizes vector error (magnitude and phase)
  • design process calculates and corrects group delay internally
  • includes sinc() response of the sample-and-hold stage in the ADC
  • optionally includes multiplierless FIR...]]> Sat, 18 Aug 2012 17:09:33 +0000 Markus Nentwig TCP/IP interface (Matlab/Octave) https://www.dsprelated.com/showarticle/169.php Communicate with measurement instruments via Ethernet (no-toolbox-Matlab or Octave)

    Purpose

    Measurement automation is digital signal processing in a wider sense: Getting a digital signal from an analog world usually involves some measurement instruments, for example a spectrum analyzer. Modern instruments, and also many off-the-shelf prototyping boards such as FPGA cards [1] or...]]> Sun, 17 Jun 2012 12:38:08 +0000 Markus Nentwig Weighted least-squares FIR with shared coefficients https://www.dsprelated.com/showarticle/165.php FIR design with arbitrary routing between delay line and coefficient multipliers.

    Includes a commented implementation of a generic IRLS FIR design algorithm.

    Introduction: Reverse Engineering

    While looking for numerical IIR filter optimization, a Matlab program in [1] for the design of FIR filters caught my attention. The equations looked familiar, sort of, but on closer examination the...]]> Thu, 24 May 2012 00:22:41 +0000 Markus Nentwig Instant CIC https://www.dsprelated.com/showarticle/163.php Summary:

    A floating point model for a CIC decimator, including the frequency response.

    Description:

    A CIC filter relies on a peculiarity of its fixed-point implementation: Normal operation involves repeated internal overflows that have no effect to the output signal, as they cancel in the following stage.

    One way to put it intuitively is that only the speed (and rate of change) of every...]]> Tue, 08 May 2012 13:48:06 +0000 Markus Nentwig Design study: 1:64 interpolating pulse shaping FIR https://www.dsprelated.com/showarticle/156.php This article is the documentation to a code snippet that originated from a discussion on comp.dsp.

    The task is to design a root-raised cosine filter with a rolloff of a=0.15 that interpolates to 64x the symbol rate at the input.

    The code snippet shows a solution that is relatively straightforward to design...]]> Mon, 26 Dec 2011 23:33:51 +0000 Markus Nentwig Bank-switched Farrow resampler https://www.dsprelated.com/showarticle/149.php A modification of the Farrow structure with reduced computational complexity.Compared to a conventional design, the impulse response is broken into a higher number of segments. Interpolation accuracy is achieved with a lower polynomial order, requiring fewer multiplications per output sample at the expense of a higher overall number of...]]> Sat, 13 Aug 2011 11:19:36 +0000 Markus Nentwig A multiuser waterfilling algorithm https://www.dsprelated.com/showarticle/119.php Hello,this blog entry documents a code snippet for a multi-user waterfilling algorithm. It's heuristic and relatively straightforward, making it easy to implement additional constraints or rules.I rewrote parts of it to improve readability, but no extensive testing took place afterwards. Please double-check that it does what it promises.

    Introduction to multiuser waterfilling.

    Background...]]> Fri, 05 Nov 2010 04:46:17 +0000 Markus Nentwig Least-squares magic bullets? The Moore-Penrose Pseudoinverse https://www.dsprelated.com/showarticle/112.php Hello,

    the topic of this brief article is a tool that can be applied to a variety of problems: The Moore-Penrose Pseudoinverse.While maybe not exactly a magic bullet, it gives us least-squares optimal solutions, and that is under many circumstances the best we can reasonably expect.

    I'll demonstrate its use on a short example. More details can be found for example on Sun, 24 Oct 2010 14:56:19 +0000 Markus Nentwig Radio Frequency Distortion Part II: A power spectrum model https://www.dsprelated.com/showarticle/111.php This article presents a ready-to-use model for nonlinear distortion caused by radio frequenfcy components in wireless receivers and linear transmitters. Compared to the similar model presented in my earlier blog entry, it operates on expectation values of the the power spectrum instead of the signal itself: Use the signal-based model to generate distortion on a signal,...]]> Mon, 11 Oct 2010 18:54:21 +0000 Markus Nentwig Understanding Radio Frequency Distortion https://www.dsprelated.com/showarticle/108.php The topic of this article are the effects of radio frequency distortions on a baseband signal, and how to model them at baseband. Typical applications are use as a simulation model or in digital predistortion algorithms.

    Introduction

    Transmitting and receiving wireless signals usually involves analog radio frequency circuits, such as power amplifiers in a transmitter or...]]> Sun, 26 Sep 2010 14:18:29 +0000 Markus Nentwig A brief look at multipath radio channels https://www.dsprelated.com/showarticle/32.php Summary: Discussion of multipath propagation and fading in radio links

    Radio channels, their effects on communications links and how to model them are a popular topic on comp.dsp. Unfortunately, for many of us there is little or no opportunity to get any "hands-on" experience with radio-related issues, because the required RF measurement equipment is not that easily available....]]>     Wed, 31 Oct 2007 16:53:29 +0000 Markus Nentwig     Delay estimation by FFT https://www.dsprelated.com/showarticle/26.php This article relates to the Matlab / Octave code snippet: Delay estimation with subsample resolution It explains the algorithm and the design decisions behind it.

    Introduction

    There are many DSP-related problems, where an unknown...]]> Sat, 22 Sep 2007 11:48:26 +0000 Markus Nentwig Polyphase filter / Farrows interpolation https://www.dsprelated.com/showarticle/22.php Hello,

    this article is meant to give a quick overview over polyphase filtering and Farrows interpolation.

    A good reference with more depth is for example Fred Harris' paper: http://www.signumconcepts.com/IP_center/paper018.pdf

    The task is as follows: Interpolate a band-limited discrete-time signal at a variable offset between samples.In other words:Delay the signal by a given amount with...]]> Tue, 18 Sep 2007 19:47:40 +0000 Markus Nentwig Through the tube... https://www.dsprelated.com/showarticle/19.php Hello all,

    something completely different...

    there was some recent discussion on the forum about modeling guitar amplifiers.I have been wondering for quite a while, whether the methods that I use to model radio frequency power amplifiers might also work for audio applications.

    It's been a rainy day, so I found the time and energy for some experiments. Just for fun.

    The device-under-test is a...]]> Sat, 15 Sep 2007 21:52:02 +0000 Markus Nentwig