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26 votes
Accepted

Why do we need DFT when we already have DTFT/DTFS?

The answer is the same to the question: "Why do we need computers to process data when we have paper and pencil?" DTFT as well as the continuous-time Fourier Transform is a theoretical tool ...
robert bristow-johnson's user avatar
15 votes

Why do we need DFT when we already have DTFT/DTFS?

TL, DR: world pervasive algorithms (FFT-related)! The continuous Fourier transform, the Discrete-time Fourier transform (DTFT) and the Discrete Fourier transform (DFT) share conceptually similar ...
Laurent Duval's user avatar
13 votes
Accepted

Why can't quantization noise be zero?

Why then we still have $ \Delta^2 \over 12 $ quantization noise You need to read more closely: this is the quantization noise for continuous-uniformly distributed signal amplitudes and equally spaced ...
Marcus Müller's user avatar
10 votes
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Increasing SNR and Dynamic Range using Oversampling

OP clarified that the question in the comments as follows: If we ignore any modulation for now and assume that we are receiving pure tones plus the band limited noise and we try to improve the SNR in ...
Dan Boschen's user avatar
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9 votes

Why can't quantization noise be zero?

Strictly speaking, there is no stochastic process that's injecting uniformly distributed random noise at the output of an ADC converter, on the interval $n \in \left (-\frac{LSB}{2}, \frac{LSB}{2} \...
TimWescott's user avatar
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7 votes
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DC bias from ADC in frequency detection scenarios

You're spot on: whereas other frequencies are typically subject to noise that is somewhat benign shaped and result of random processes, DC is usually affected by things like a DC offset. Physically, ...
Marcus Müller's user avatar
6 votes
Accepted

Higher order harmonics during sampling

The sampling is indeed analogous to mixing as to my understanding. In the sampling process, we multiply the time domain signal with an impulse train - the impulses in time are represented as impulses ...
Dan Boschen's user avatar
  • 52.8k
6 votes
Accepted

confusion sampling vs quantization?

Sampling is the process of making the x-axis (time) discrete and quantization is the process of making the y-axis (magnitude) discrete. You can sample without quantization (such as done with an ...
Dan Boschen's user avatar
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6 votes
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DAC and ADC architecture in SDRs

To add here are two diagrams showing common transceiver architectures: (1) a super-heterodyne where the down-conversion is done first to an IF frequency and then to baseband and (2) a zero-IF receiver ...
Dan Boschen's user avatar
  • 52.8k
6 votes

Increasing SNR and Dynamic Range using Oversampling

When referring to the SNR achieved by oversampling, we have to be careful in using the term "SNR". There are essentially two SNR's to consider: The SNR that is the signal-to-quantization-...
Envidia's user avatar
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6 votes
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Why does twice the sampling rate (Nyquist Theorem) seem inadequate?

Perfect recovery is one thing, niceness is another. Sampling above x2 Nyquist is sufficient for perfect recovery, after which we can FFT-upsample to make it look nice - which is more efficient than ...
OverLordGoldDragon's user avatar
6 votes
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Building a data acquisition system to capture raw IQ data

As a front-end radio designer with experience in the microwave frequency ranges, I concur with the advice to just buy a solution such as the ADALM-PLUTO SDR Learning Module. However that particular ...
Dan Boschen's user avatar
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5 votes
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Why use a 1-bit ADC in a Sigma Delta Modulator?

First of all, because it's easy to build a 1-bit ADC. It's a comparator. It's literally the easiest ADC you can build. The $\Delta\Sigma$ ADC was invented (or, rather, published) in 1962ยน ! The 2-bit ...
Marcus Müller's user avatar
5 votes
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How do you simultaneously undersample and oversample?

Undersampling is also known as "bandpass sampling" and "IF sampling". Consider the sampling of an 11 Hz sine wave and a 1 Hz sine wave, both sampled by a 10 Hz sampling clock as ...
Dan Boschen's user avatar
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5 votes
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Quantization Noise for Coherent Sampling - Phase Noise?

I have a doubt about (Edit: this was later removed from the question): The distribution of these AM and PM noise components can be reasonably assumed to be uniform as long as the input signal is ...
Olli Niemitalo's user avatar
5 votes

Bandwidth with complex sampling

Complex sampling does not "break" Nyquist. IQ quadrature sampling produces twice as many bits per second of information (at the same sample rate for real or complex samples), and the 90 ...
hotpaw2's user avatar
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5 votes
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Are there analog re-configurable filters?

can we have re-configurable analog filters? Yes. The knob you turn on your grandma's kitchen or living room radio changes the tuning of an oscillator by changing the capacitance of a component. Any ...
Marcus Müller's user avatar
5 votes
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I/Q sampling with just one ADC

Is this an entirely stupid idea? No, but you've just came to the conclusion that instead of sampling complex, with Nyquist rate being the bandwidth, you should do twice as many samples. That simply ...
Marcus Müller's user avatar
5 votes
Accepted

ADC sampling rate and signal bandwidth for FHSS

So for frequency hopping spread spectrum (FHSS),when the receiver is unaware of the transmitter's hopping pattern, does that mean the ADC sample rate needs to be higher than twice the entire hopping ...
TimWescott's user avatar
  • 12.9k
5 votes

Building a data acquisition system to capture raw IQ data

Can you use any of the NI DAQ modules? Or does it need to be designing/soldering an RF front end from scratch and then reading it on some embedded processor/doing some FPGA? I think option (1) is ...
Ash SDR's user avatar
  • 133
5 votes

Building a data acquisition system to capture raw IQ data

I'd suggest buying a Adalm Pluto board. It's very inexpensive.
Dan CaJacob's user avatar
5 votes

Building a data acquisition system to capture raw IQ data

As Dan mentioned , check ADAM Pluto This might be a good starting point . I didn't look at the lab tutorials 1 and 2 and electronic tutorials 1 and 2 , but looks promising. You can probably order the ...
Ash SDR's user avatar
  • 133
5 votes
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SQNR vs SNDR (with regards to Delta Sigma Modulation)

The difference is SNQR is the SNR due to quantization noise alone as a theoretical limit while SNDR (also referred to as SINAD) includes multiple distortion sources in addition to quantization. SINAD ...
Dan Boschen's user avatar
  • 52.8k
5 votes

Difference between ADC dynamic range and voltage resolution?

ADC resolution is the level of one quantization step in the units of magnitude desired (such as volts to refer to the input, or counts to refer to the digital output levels). The resolution is the ...
Dan Boschen's user avatar
  • 52.8k
4 votes

Does delta-sigma ADC also reduce Gaussian noise on input signal to ADC or just quantization noise?

No! The ADC (delta sigma or not) can not reduce the uncertainty in the input. It sounds to me that your friend has not made up a real signal flow diagram and then formed equations. The answer to ...
rrogers's user avatar
  • 425
4 votes

Is it theoretically possible to perfectly quantize a continuous signal?

I'd like to point out Heisenberg Uncertainty principle, based on which theoretical achievable precision is limited. It states that one can not measure two complementary qualities (e.t. here time and ...
MimSaad's user avatar
  • 1,976
4 votes

comparison between Fourier transform and autocorrelation function

Signals can be classified in many ways, and one of them is according to their nature such as being deterministic or random (stochastic). When a signal is deterministic, its spectral content is given ...
Fat32's user avatar
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4 votes
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Calculating SFDR from FFT of ADC output

I would tend to believe that there is an indeed a flaw in the approach as the datasheet SFDR is achievable given the test conditions which are usually specified in the datasheet as well. 23 dB is ...
Dan Boschen's user avatar
  • 52.8k
4 votes
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How we can quantize a sampled signal in MATLAB?

First you will need to determine the number of quantization levels. I am going to assume a power of two for digital convenience's sake. ...
ambitiose_sed_ineptum's user avatar
4 votes
Accepted

DSP low pass filter (IIR) no longer works when changed to a new MCU

I2S audio samples are signed two's complement. Just add $2^{N-1}$, where $N$ is the number of bits, to the result, and binary and by $2^N-1$, to get the range to $0\...
Olli Niemitalo's user avatar

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