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    Transistor noise test circuit from 'The Art of Electronics' doubt

    That was extremely helpful. Thanks a lot erikl. I'm planning to replace the upper part with just batteries, and forget about the noise from the supply lines. But I will use 9+3 V getting 12 V instead of 12.5 V as specified in the circuit. I don't fully understand how the feedback circuit sets...
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    Transistor noise test circuit from 'The Art of Electronics' doubt

    Hello! I'm planning to use a circuit attached (from 'The Art of Electronics 3rd Edition') to measure the noise of some fast low noise npn I got. But it is not really well described in the book. I don't get the use of the "pre-insertion" and R4. Also I don't understand the use of the small...
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    Recording audio with smartphone mic input. White noise

    Exactly, that's what I meant Audioguru. I tried to check if the smartphone was the responsible, recording the "silence" by shorting the 3.5 minijack input (between MIC and Ground channels of the CTIA/AHJ standard) and the hiss was still there...
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    Recording audio with smartphone mic input. White noise

    Thanks a lot guys for the nice input about microphones' response. But I'm a bit puzzled. From my naive point of view I think I should not be concerned about that. I mean, I'm trying to record electric signals directly from guitar/guitar amp / digital keyboard headphones output to my...
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    Recording audio with smartphone mic input. White noise

    Hi! I decided to solder a 3.5mm 4-pol phone connector to a 6.35 mm one in order to record electrical instruments (guitar, keyboard... maybe mixing desk too) directly in my smartphone. You can see the first version of this "adapter" in the picture attached. I used it together with two apps...
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    Concatenation of current NOISE sources in series

    Dear all I've been playing around with simulated equivalent input current noise in LTSpice and I found out that, in the same way it works when you have two DC current sources in series, the maximum current noise you get is the one set by the lowest contributor. For example: In a simple...
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    Simple question about saturated transistor circuit (from OpAmps for everyone)

    Hello everyone! I was reading OpAmps for everyone (available here) and found something strange on page 37. Does anyone know if the I_L they use is the current flowing through a possible load resistor (i.e. 50 ohms) connected from V-out / V_C to ground? For me what it does not make sense is...
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    (Photodiode Model) Equivalent components when using voltage source as input

    Thanks a lot for your answers. First, sorry, that is something I didn't mention but the photodiode will be reverse biased (high frequency response). The Vbias in the schematic will be 5 V. Audioguru I don't get why you say the photo-diode is not a current source when reverse-biased. With...
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    (Photodiode Model) Equivalent components when using voltage source as input

    Hi! First I want so say that I'm already familiar with the equivalent electrical circuit of a photodiode you can find in the bibliography. But the thing is I'm having troubles in something I thought it should be straight forward. I want to build a new OpAmp-based transimpedance amplifier for...
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    Discrepancy between experimental measurement and LTSpice noise simulation

    Well, I run a simulation with Genesys and a more accurate model of the transistor (S-parameters for Ic= 1 mA and Vce = 1.5V - I have Vce= 1.636V)... and look. It seems that the LTSpice's model is waaaay off. I could not find any other model for my BFR181 than this BFR181/SIE... but anyway...
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    Discrepancy between experimental measurement and LTSpice noise simulation

    It's a double sided PCB, with mainly MINIMELF Resistors and other SMD components...
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    Discrepancy between experimental measurement and LTSpice noise simulation

    Actually I tried it yesterday, by plugging in the output of a Network Analyzer into the bjt's base (as in the LTSpice schematic) and measured the transfer function in the frequency range. And it was 5.5 dB higher than in LTSpice (41.5 dB vs 47 dB).... First, I don't understand this discrepancy...
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    Discrepancy between experimental measurement and LTSpice noise simulation

    That's what I meant at the beginning with "The 50 Ohms load in the LTspice simulation represents the input impedance of the Spectrum Analyzer." So in the implemented circuit, the 50 Ohms of load are not there, and I measure the output voltage noise density being this voltage the one over the...
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    Discrepancy between experimental measurement and LTSpice noise simulation

    I just checked, and it looks almost the same in both situations: LTSpice Ic = (Vp-Vc) / Rc = (5 V - 0.796 V) / 3.9 K = 1.077 mA Measured (Multimeter) dcOP Ic = (Vp-Vc) / Rc = (5.04 V - 0.862 V) / 3.9 K = 1.071 mA I also checked all resistors values (to verify the non-inverting amplifier...
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    Discrepancy between experimental measurement and LTSpice noise simulation

    Hi guys! I wanted to compare the simulated noise in LTSpice with the experimental result measured using a Spectrum Analyzer (hp4395A) and I built the circuit you can see in the attached picture. The 50 Ohms load in the LTspice simulation represents the input impedance of the Spectrum...
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    S-Parameters to voltage transfer function relation

    Got it, the wire example helped a lot! Thanks!
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    S-Parameters to voltage transfer function relation

    The pic attached shows the network I'm testing. according to what I've read about the S parameters, S21 would be Vout/Vsrc. My circuit would be the one without the input source and the 50 ohms in series, and also without the final 50 ohms load. What do you mean by unloaded? Wouldn't the source...
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    S-Parameters to voltage transfer function relation

    Hello guys, Simple question whose answer I can't find properly explained anywhere... What is the relation (in linear scale) between the s-parameters, let's say S21, and the voltage transfer function, Vo/Vi for a 50 Ohms matched system? I checked many sites and sometimes it is basically that...
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    Software to fill the gap between LTSpice and reality

    Dear all, I've been looking for different options to solve this ancient problem I had. I focus on high-speed (~50MHz) photoreceiver design (including opamp and discrete element topologies) and I've encountered problems due to the discrepancy between the spice/circuit theory estimations and the...
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    Unexpected behavior in the freq response of my transimpedance amplifier design

    Hi guys, Unfortunately I'm back here. I thought it would be all joy and fun with the simpler series topology (within its limitations) but I found sth else that I don't know how to deal with. I attach the TF of this last circuit, and as you can see, there is a peak at approx 240 MHz (and...

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