# 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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36 views

### Temperature sensor noise

I am trying to model a temperature sensor in Simulink. I have a question regarding the modelling of the temperature noise. I was thinking of modelling it as a band limited white noise, but I am unable ...
27 views

### How to calculate the noise root-spectral-density of below switched-capacitor circuit?

I have the following question: How the noise density of below circuit with output node “out2” is calculated? How the simulator came to a value of “-178.3 dBVrms/sqrt(Hz)”? For me is clear, for the ...
47 views

### Can an LNA noise figure be normalized to dBm to estimate the minimum detectable signal?

If a device claims a noise figure of 0.3 dB NF such as the Qorvo QPL9547, can you calculate the dBm value of a signal that is at the noise floor (ie, a barely detectable signal)? Otherwise stated: I ...
62 views

### how to calculate the phase noise contribution of an active loop filter in pll

I want to calculate the contribution of each phase-locked loop(pll) module to the total phase noise that has been done in ADIsimPLL. But I'm having trouble calculating the contribution of the loop ...
136 views

### Spectrum of Mains Power Line Noise -- Peculiar Frequencies

I am trying to understand the noise induced in wires running adjacent to a mains power line. For that purpose, I took about 4 meters of extension cord and 4 meters of RG6 coax and tied them next to ...
116 views

### What determines noise spectral density of diode-resistors?

One common way to think of a diode is that it is a variable resistor, whose resistance depends on its voltage drop and can be controlled via its bias current. I have two questions about how far this ...
1 vote
116 views

### How to reconcile units in accelerometer noise density

I am trying to model an accelerometer in MATLAB. It is asking for the noise density in (m/s^2)/sqrt(Hz). The datasheet for the IMU I am trying to model gives output noise in (m/s) for the 100Hz ...
1 vote
96 views

### Voltage RMS and Voltage Spectral Density from ADC Sample are Not Consistent

I have time series data from a 100 MS/s ADC, and I would like to calculate the RMS noise and the voltage spectral density (VSD), and see consistency between the two. I'm using a 16-bit ADC, and the ...
284 views

### Noise figure to voltage noise spectral density hand calculation

The RF LNA of interest is the PGA-105+ from mini-circuits. From only the gain and noise figure I calculated the voltage noise spectral density that would be present at the amplifier input. If anyone ...
47 views

### Effect of Antenna and gain on PSD of a radio receiver

I have a cheap SDR receiver and today I was trying to measure the noise in the system. I tried to disconnect the antenna and measure the power over the frequency range of the device. I also decided to ...
118 views

### Why does current noise flow through the parallel combination of R1 and RF in a non-inverting opamp?

I am following this reference for noise calculations of a non-inverting op-amp. I am not able to understand why the equivalent resistor is the parallel combination of R1 and RF as shown below: I ...
44 views

### What does it mean when the output of an auto co-rrelation function is the unit impulse at t=0?

I read that auto-correlation function of white noise is unit impulse at t=0 is of strength N0/2. What does it mean that it is a unit impulse at t=0 ?
183 views

### Amplitude Spectral Density from a Fast Fourier Transformation

I want to calculate the Noise-equivalent Power (NEP) of a photodetector. Hereto, I have to measure the Amplitude Spectral Density (ASD) of the detector and divide the result by the Responsivity: The ...
1 vote
115 views

### Noise equivalent power of thermopile sensor?

I am working on the characterisation of thermopile sensor and stuck in determining the NEP of the sensor. My thermopile sensor with AD8630 amplifier receives IR radiation coming from the blackbody at ...
1 vote
60 views

### OP amp noise density and Johnson noise (Thermal noise) for 16bits ADC

I am trying to create a analogique amplification chain between a piezo sensor (10mVPP) and 16 bits ADC in 3V3 range. I try to simulate the chain on LTSpice to get the lower noise density I can get. @...
82 views

### How does Ohm disappear in noise/power spectral density unit?

Power spectral density is commonly expressed in Watts per Hertz ($W \over Hz$) or $V \over \sqrt{Hz}$. When I try to derive these for a resistor I get confused on the units. If we define noise ...
217 views

### What causes flicker or 1/f noise?

What physical processes causes the generation of electrical and radio/EM/RF flicker or 1/f noise? Or why are those sources not generating normally distributed electrical observables (such as thermal ...
1 vote
54 views

### RC noise figure calculation

I would ask for some help with noise figure calculation for circuit attached. It is front end of improvised differential probe that I would like to build. I am aware that simulators such as LTSpice ...
160 views

### Understanding Noise Figure of LNA (HP 461A amplifier)

I have recently got a HP 461A linear amplifier (from the 60's) which works from 1Khz to 150Mhz. I have checked that: it's input gives a SWR <1.1 across all spectrum (i.e., the input impedance is ...
56 views

### Measuring Noise Contribution of Amplifier in Antenna Amplifier System

I have a very simple setup that looks like the following: It is simply an antenna connected in series to an amplifier. The output of this setup goes to a spectrum analyzer where I measure some power (...
113 views

### 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 ...
1 vote
201 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 ...
449 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 ...
221 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 ...
56 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 ...
643 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 ...
47 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 ...
56 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 ... 216 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 ...
1 vote
59 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 ...
121 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 ...
90 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 ...
468 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 ...
79 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?
86 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 ...
1 vote
157 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 ...
107 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 ...
101 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 ...
567 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 ...
87 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-...
97 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 ...
2k 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 ...
77 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 $H_2(\omega)$. ...
1 vote
1k 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 ...
595 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 ...
151 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 ...
1k 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 ...
93 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 ...