 ### Dan Boschen (@DanBoschen)

Background: Wireless communication physical layer hardware implementations from antenna to modem both in analog and digital domains; Microwaves & RF, Analog, Data Conversion, and Digital (FPGA). Dan is an engineer at Microchip (Formerly Microsemi, formerly Symmetricom) and teaches DSP and Python for the IEEE and DSPRelated.

## Re: Sigma-delta DAC or delta-sigma DAC?

The Sigma is the accumulator (for Sigma-Delta DAC) or integrator (for Sigma-Delta ADC as shown below) just prior to decision and feedback. The output of the decision...

## Re: Sigma-delta DAC or delta-sigma DAC?

They are both the same thing and used interchangeably. I must admit that I use both depending on how I wake up in the morning. My impression is Sigma-Delta is more...

## Re: CIC implement question?

I agree with you that the CIC still has viable applications but don't agree that "single bit is very limited". In particular we are seeing more and more single...

## Re: Electromagnetic waves question

... I use the DFT to synthesize antenna patterns in multi-element arrays for this reason. I love it when disciplines overlap to the same underlying principles!

## Re: The Anatomy of a Finite Impulse Response

I love new intuitive ways of looking at things. Kudos!

## Re: The Anatomy of a Finite Impulse Response

Thanks yes I can't underline enough how much visualizing phasors and working with complex signals simplifies the intuition for DSP. My courses start with this in...

## Re: The Anatomy of a Finite Impulse Response

Nice question Kaz! Is “The frequency response is the Fourier Transform of the Impulse Response” an insufficient intuition for you? Perhaps then more intuition...

In most depictions of the standard forms, the feedback coefficients are negated. This is just convenient convention based on how the transfer function as given maps...

## Re: The Anatomy of a Finite Impulse Response

The intuition of converting the symmetric or antisymmetric coefficients to real sinusoidal components is helpful for the large subset of all possible FIR filters...

## Re: CIC implement question?

Ah ok! Good clarification- that makes a lot of sense. So in applications where down-sampling is to be done on a multi-bit signal, perhaps the CIC is still a viable...

## Re: CIC implement question?

Very nice fred!!! I laughed out loud at all the intro slides. Yes CIC very bad with floating point. I believe with fixed point we can overflow once with no consequence...

## Re: CIC implement question?

I don’t think you are necessarily “wrong” in your thought process - it is just a matter of being clear on how the frequency axis is scaled. Each block on its...

## Re: CIC implement question?

The z^{-1} blocks shown represent a one sample delay for the sampling rate of that block. With that view, they are all correct as Mth order CIC decimate by 2 filters. Be...

## Re: Correlated phase noise

Krishk- Did the update get to the root of your question or is there still some confusion here? It may help to know that for small angles beta, the sidebands due...

## Re: Effect of decimation, tuning (mixing) on phase noise

An NCO is equivalent to a fractional divider of the master clock. In general when you divide any frequency tone with phase noise by \$N\$, the phase noise goes down...

## Re: Effect of decimation, tuning (mixing) on phase noise

I have seen "DDS" referred to the combination of an NCO with a D/A (meaning providing an analog output) whereas an NCO is providing a digitally generated source....

## Re: Correlated phase noise

I updated that post to focus on the phase noise cancellation, bottom lined here:This occurs in down-conversion only and not in up-conversion given the output in...

## Re: Difference between averaging and decimation on oversampled data

Often decimation filtering is done very simply with averaging: a CIC decimation filter is mathematically equivalent to a moving average over D samples followed...

## Re: fft process gain revisited

Yes, no disagreement with that. I was trying to provide an explanation how it is the same and yet the same processing gain concepts apply (but apparently I didn't...

## Re: fft process gain revisited

This does apply equally in reverse, and you are correct that the operations are symmetric other than the sign on the exponential. Further by convention we scale...

## Re: fft process gain revisited

Hi David-The FFT is a narrow band filter, and the quantization noise (up to the limits of the SFDR) is spread evenly across all bins, so you can get a lot more bits...

## Re: fft process gain revisited

Sorry for my distraction about bin power spread due to windowing which is my preferred use of processing gain in an FFT. My bigger point was there is no actual change...

## Re: fft process gain revisited

A noise density is an easier way I think to view this, as the noise density (in power/Hz specifically NOT power/bin) for spread waveforms (such as quantization...

## Re: Single-bit long-range low-power communication

No the power spectral density will remain constant if the transmitter transmits at a constant power the same waveform (since the PSD is the power spread over frequency). There...

## Re: ChatGPT's idea of a computationally efficient digital filter - ha ha ha...

Randy- I was curious too! See https://dsp.stackexchange.com/questions/85937/pole...

## Re: Single-bit long-range low-power communication

Time varying channels due to Doppler and multipath will be a big limitation. If there are no other temporal variations (such as Doppler from movement or channel...

## Re: Is there any reliable implementation method of IIR filters with pole positions very close to the unit circle?

Love it, very clever.

## Re: IIR filters

A resampled FIR is also a very good solution for this case (even decimating to implement the LPF and interpolating after if the higher sampling rate is needed)....

## Re: IQ mag: Integer approximation of square root of the sum of two squares

Related but those don’t really fit the bill as they are used to compare two complex magnitudes rather than estimate the complex magnitude. However what I didn’t...

## Re: IQ mag: Integer approximation of square root of the sum of two squares

Very nice Rick! I didn't know that, thanks for the additional history and nice work. Until I reread the post, I was going to go forward from this point thinking...

## Re: IQ mag: Integer approximation of square root of the sum of two squares

This is the "Alpha Max + Beta Min" algorithm as a high-speed approximation for the magnitude of a complex number (or more generically the square root of the sum...

## Re: #OFDM sample rate

If the RF Bandwidth is 10 MHz there is no need to sample at or more than 30.72 MHz assuming complex baseband samples  —sampling at twice the FFT sampling rate...

## Re: 'near IQ' sampling

This is also referred to as “undersampling”. Key requirements and considerations to do this properly are that the analog input bandwidth of the ADC surpasses...

## Re: correlation of two complex signals

Yes you are correct and that Matlab and Octave do the expected conjugation. Apparently your signal has been already conjugated which can occur when the spectrum...

## Re: correlation of two complex signals

What may be missing is the complex conjugate that is required when doing a complex correlation. Correlation is the integration of the complex conjugate product of...

## Re: Coherent re-sampling

Have you considered windowing prior to the FFT? This will minimize the spectral leakage at the expense of widening the main lobe (frequency selectivity). Given you...

## Re: Modelling a RF amplifier in Python

I recommend modeling the baseband equivalent signal which is the complex magnitude and phase versus time (the analytic signal moved to DC). There is no reason to...

## Re: Do we have to insert the DC null in OFDM when using RF direct sampling ADC architecture?

Thanks, that is handy! The derivation now that I think about it seems straightforward. What we see is we are just lowering "S" in SNR directly: SNR = 20Log(Sine...

## Re: Do we have to insert the DC null in OFDM when using RF direct sampling ADC architecture?

The formula SNR = 6 dB/bit + 1.76 dB is insensitive to DC offsets. This result comes from the variance of a uniform distribution as being q/12. If you apply that...

Use this form to contact DanBoschen

Before you can contact a member of the *Related Sites:

• You must be logged in (register here)
• You must confirm you email address