26
votes
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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 ...
- 21.4k
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 ...
- 32.3k
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 ...
- 32.5k
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 ...
- 55k
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} \...
- 13.3k
7
votes
Accepted
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 ...
- 55k
7
votes
Accepted
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, ...
- 32.5k
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 ...
- 55k
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 ...
- 55k
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-...
- 2,936
6
votes
Accepted
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 ...
- 9,242
6
votes
Accepted
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 ...
- 55k
5
votes
Accepted
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 1962¹ !
The 2-bit ...
- 32.5k
5
votes
Accepted
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 ...
- 13.7k
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 ...
- 35.7k
5
votes
Accepted
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 ...
- 32.5k
5
votes
Accepted
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 ...
- 32.5k
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 ...
- 13.3k
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 ...
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5
votes
Building a data acquisition system to capture raw IQ data
I'd suggest buying a Adalm Pluto board. It's very inexpensive.
- 61
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 ...
- 133
5
votes
Accepted
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 ...
- 55k
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 ...
- 55k
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 ...
- 1,976
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 ...
- 425
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 ...
- 55k
4
votes
Accepted
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.
...
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\...
- 13.7k
4
votes
Accepted
Using oversampling to increase resolution of a DC-signal as input
My input signal is a dc signal (sensor output) and im getting kind of a headache to understand why oversampling can increase the resolution of dc signals.
The ADC puts out integers. So, let $x$ be ...
- 13.3k
4
votes
Condition for aliasing
There really is no practical difference between the two. The important thing to understand about aliasing is not the exact definition of the word, but rather the concept: when two frequency bands ...
- 156
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