# Questions tagged [noise-spectral-density]

Anything related to the noise spectral density, i.e. the function representing how the power of the noise signal is distributed among its frequency components.

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### What is the math behind high FM frequency components being more noise prone? [closed]

what is the math behind the phenomena that higher frequencies are more prone to noise? The use of pre-emphasis to boost the higher frequency components to get a better S/N ratio. Can you provide ...
53 views

### Is noise density over a bandwidth a measure of the noise's standard deviation?

Suppose I have a sensor which has a dominant white gaussian noise source, a $1\textit{unit}/\sqrt{Hz}$ noise density and a bandwidth of 100Hz. Then the noise becomes 10$units$. Is this a measure ...
24 views

### From noise spectral density to equivalent short circuit input RMS noise

I have an acquisition system that is supposed to be low noise. It acquires from an ADC into a wav file. I read this file and process it with Matlab. Then, being "x" the array with time signal, Fs the ...
201 views

### Help figuring out what is the limiting factor on the noise level in this analog optocoupler circuit

I am trying to build a circuit that takes a {-10V ... +10V} analog signal and outputs the same {-10V ... +10V} voltage but galvanically isolated from the input. The idea is similar to that of digital ...
121 views

### What noise frequencies is an oversampling ADC susceptible to?

When calculating the input-referred noise and filtering to a 24-bit sigma-delta ADC (MCP3561), I hit a roadblock. Knowing the noise spectrum density (nV/sqrt(Hz)) of a signal noise source, like ...
34 views

### Simulation of the injected noise to oscillator in Virtuoso

I have a differential LNA that injects current to an oscillator. I want to see the thermal noise injected to the oscillator. This noise is composed of the noise of oscillator + noise of the LNA. Now ...
359 views

### What are the calculations to do in practice to estimate beforehand the noise seen on the output of this op amp circuit?

I would like help with understanding something better, but am not trained in electronics so please bear with me! I am trying to make a simple circuit to take a {-10V ... +10V} signal from a function ...
36 views

### Total thermal noise of a photodetector connected to a spectrum analyzer

I connected a photodetector to a spectrum analyzer (SA) and observed the signal (i.e. noise) on the SA when there is no light hitting the detector. I noticed that when I set a low spectral resolution ...
50 views

### Power spectral density on the output of frequency modulator?

Is there a formula with which we would be able to calculate the power spectral density on the output of a frequency modulator? The information we know is that we have a receiver working in 180MHz ...
82 views

### Can we use both FFT and PSD to obtain a random signal's frequency domain representation?

I always encounter random noise frequency domain representation as PSD(not FFT), something like in the below plot: Without diving into math too much, practically speaking can we always use FFT ...
52 views

### Phase noise of a digital PLL

I assume the reader is aware of how a DPLL works. The DPLL oscillates with a frequency of $F_{out}$. The DCO free running frequency is $F_{free}$. In the model of our DPLL we've only considered ...
27 views

### How does spectral density of a power signal change when it is multiplied by $cos(2\pi f_ct)$?

Suppose we have a power signal $n(t)$ whose power- auto-correlation function is: $R_{n}(\tau)$ . Now we multiply the signal by a cosine as: $cos(2\pi f_ct) \cdot n(t)$, whose auto-correlation is ...
69 views

### How does one calculate output voltage noise of a current output DAC?

I am using a current output DAC connected to a voltage reference and a transimpedance amplifier. I know the noise characteristics of the voltage reference and the amplifier. The DAC simply lists "13 ...
48 views

### Does the profile of phase-noise power spectrum density (PSD) vary with time?

I will promptly provide any detail or revise my question aimed at any feedback. Does the profile of phase-noise power spectrum density (PSD) vary with time? The conclusion may be that it won’t ...
142 views

### Johnson-Nyquist noise for a lossy inductor?

In searching the internet for thermal noise on an inductor and I'm not finding much on the basics for a real lossy inductor. I'm interested in thermal noise for a fixed inductor in a surface mount ...
65 views

### The mean value of phase noise as a stochastic process

What is the mean value of phase noise as a stochastic process? Where can I get a theoretical analysis of this topic?
53 views

### Noises of switching power supply

I made a switching power supply (input: 24VDC, output: +-15Vdc) for LEM (current sensor). Noises of the power supply caused the output of LEM to become a bad waveform, but I don't know how to ...
91 views

### Maximum Allowable Noise of ADC Input Signal

I have a question about calculating the maximum allowable noise for an ADC signal conditioning stage. I have an existing signal conditioning stage as well as an ADC on a microcontroller. I would ...
62 views

### Noise Spectral Density Standard

Is there an IEEE or other standard for how Noise Spectral Density is calculated? In particular, when they give a single figure (like $12.4\,\text{nV }/\sqrt{\text{Hz}}$) is that averaged over the ...
80 views

### noise of high speed serial link

I have an ADC module. The board contains sensitive (10-100MHz) analogue parts and a high speed serial link (Aurora). The link uses scrambling algorithm, and I can choose the bit-rate. (I have much ...
247 views

### $pV/\sqrt {Hz}$ in Power Spectral Density

I am trying to plot a Noise Spectral Density from 10 kHz to 1 MHz. The Graph shows a cure which at 1 MHz the noise is 76 pV/rootHz. I am unable to understand that unit definition here. Becuase the ...
74 views

### Sampled Noise Amplitude

I am trying to understand how an arbitrary noise spectrum is sampled by an ADC. Let the broadband noise floor be, for example, $e_n$ = 5nV/√Hz @ 1kHz and the 1/f noise be $E_{1/f}$ = 2 μV peak-...
73 views

### Conversion of Additive Noise to Phase Noise

RF Microelectronics by Razavi contains the following snippet in section 8.7.3 concerning the analysis of phase noise in oscillators: We write $x(t)=A\cos(\omega_0t)+n(t)$ where $n(t)$ denotes ...
797 views

### How do I measure very low frequency noise?

I'd like to measure low-level noise in the 1 Hz to 100 kHz range, for example at the output of a LDO. For higher frequencies a spectrum analyzer would do the job, but most only go down to the MHz ...
72 views

### Noise in Analog communication

A signal with PSD $S_x(\omega)$ is passed through a channel with frequency response $H_1(\omega)$ and at the receiver, it is passed through an equalizer with frequency response $H_2(\omega)$. ...
347 views

### How may noise voltage and noise figure be compared?

For instance, comparing the MIC920 and the BGA2818, it's expected that since the latter is intended for application as an RF LNA and the former is general-purpose, the BGA2818 would out-perform the ...
343 views

### Filtering capacitor only adds noise in a rail-splitter

Say I need to make a very low-noise signal inverting schematic. For that I came up with the schematic below - the U2 is a low-noise opamp in an inverting configuration, and the schematic around U1 is ...
113 views

### Can I measure the voltage noise with True RMS function

I have a measurement setup with which I want to measure high voltages. Now I want to evaluate the noise this setup produces (preferably in V/sqrt(Hz)). I short circuited the input and I am now ...
529 views

### 1/f noise, is it limited?

Basically my question is: I doubt noise density goes to infinity because we can reach the limit f→0 in any DC circuit in contrast to the limit f→∞ (which is an idealization because all circuit ...
78 views

### Unit in the exponent for phase modulation

How does the "unit" per Hertz in behave in the exponent? My specific question is about the calculation of the modulation index $\eta$ from a measured spectral density of a phase modulation on a ...
3k views

### Converting Power Spectral Density to Power

I have a vector signal analyzer which is measuring an OFDM signal with a bandwidth of 20MHz. The spectrum shows "Power Spectral Density [dBm/RBW per 100kHz]" on the Y-axis. The RBW is set for 100kHz. ...
195 views

### Allan std deviation: why do we need to read the values at specific sample times?

I'm trying to deduce the white noise and rate random walk for an IMU. Some sources recommend deducing those values by fitting a line to the corresponding part of the log-log plot, and then reading the ...
40 views

### Sinusoidal signal as density

I produce a magnetic field with a current source and a long cylindrical coil. A current of $\hat{x}$ (peak value) with frequency $f_{x}$ produces a magnetic field of $B$ (RMS value in Tesla) ...
145 views

### Phase-modulated Noise

If you replace the carrier signal in a phase modulated circuit with noise then presumably the noise will be modulated. What must be considered if we wish to detect this noise modulation? I’ve ...
143 views

### Ιnput referred noise of an amplifier

I have a problem with a low noise amplifier because I can't find in ADS(Advance design system) software how to integrating under the are of a measured curve in a specific frequency range.Can someone ...
3k views

### Antiresonance of multiple parallel decoupling capacitors: use same value or multiple values?

My quesiton: Is it better practice to put same-valued capacitors in parallel of capacitors of different values to decouple the high-frequency noise caused by digital ICs? Background Digital IC need ...
3k views

### Noise Model for Zener Diodes

I am trying to design a noise source using discrete transistors and a Zener diode in the avalanche breakdown region. Therefore, I have several questions relating to the use of the diode... How does ...
549 views

### Current noise as spectral density from given RMS noise

I want to know the current spectral density of a Keithley 6221 current source. The datasheet above provides values in RMS for a given Bandwidth from $10~\text{Hz} - \text{BW}$, not clearly ...
822 views

### Determining noise spectral density

I am working with a digital sensor (magnetometer) that can operate at multiple frequencies. The application note (http://www.st.com/resource/en/application_note/dm00136626.pdf) gives RMS noise values ...
2k views

### Gyroscope Noise Density

I am trying to understand how to use the "Rate noise density" spec on a gyro IC. It is quoted at 0.25 degrees/second/root(Hertz). I plan on sampling it at about 100Hz. Is the noise going to be root(...
629 views

### Why are there two sets of ENBW correction factors?

For calculating the equivalent noise bandwidth of a non-brickwall filter, I can find two different sets of numbers, both of which claim they are similar things: ...
401 views

### Practical consequence of the noise spectral density

For a particular current transducer, http://www.digikey.com/catalog/en/partgroup/ho-p-sp33-series/49533, it states an "Output rms voltage noise (spectral density)" of 6.13 uV / sqrt{Hz}. If the ...
2k views

### What is the noise level as read on my oscilloscope?

The above is what I'm seeing on my oscilloscope. It's zener diode noise. Scope's set for 0.5V/div vertically, and 1ms/div horizontally. The oscilloscope has a 20MHz bandwidth, but the noise doesn't ...
193 views

### Noise Coupling methods to communication cables

I want to know how can I couple noise(practically) into a communication cable in order to analyze the data error rate of the communication. I hope by using transformer I can couple it, but I don't ...
2k views

### Why the noise from cascode transistors are negligible at low frequencies?

I am reading about noise of cascode amplifier in Razavi book, Design of Analog CMOS Integrated Circuits. However, I couldn't understand the yellow highlighted sentence below. Could anyone explain it? ...
312 views

### Noise in cascode opamp

Could anyone tell me how the noise current component in the red circle is calculated here? I believe the superposition method is used here but I can't figure out how to get the second component like ...
197 views

### Why the mean squared value of a random noise signal at a single precise frequency is zero?

I am reading about noise from this lecture (page 9/31). However, I don't understand this point. Could anyone explain why mean squared value is zero? The mean squared value of a random noise signal ...
2k views

### How to avoid Johnson noise in high input impedance amplifier

I don't have a circuit I'm working on, this is more of a theoretical question - I am trying to remedy a flaw in my understanding. Imagine I want to build a high input impedance amplifier to work in ...