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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

    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

    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

    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

    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 everyone! I'm working on a rather simple transimpedance amplifier (TIA) for a photodiode. I split the photodiode current into an AC and a DC path, since I need both outputs. For each of them I use a different amplifier and a different compensation capacitor. With the values you can see in...
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    Cable to connect a 120 Ohms output mixing desk to a 8 Ohms loudspeaker

    Hi everyone, I want to solder a cable to connect the main output of my mixing desk **broken link removed** (model 802, but anyway the output characteristics are the same) to an 8 Ohms loudspeaker. I used it in the past with headphones (higher impedance) or some other self amplified loudspeakers...
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    [Understanding an undescribed circuit] Integ./Power Stabilization using OpAmp Chain

    Hello fellas, I'm performing some measuremennts with a laser diode, testing the spatial response of a photodiode. Since my measurements are not as accurate as I would like them to be, I want to use a power stabilization system to achieve some improvement. The thing is that some devices are...
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    OpAmps: Strange Frequency Response. Photoreceiver Circuit. AC-DC channel division.

    [For everyone: I want to say sorry in advance for my mistakes writting in english] Hello Fellas, I designed a TIA photoreceiver circuit in order to obtain an output voltage from a input current coming from a photodiode. The schematic of the design and the simulation of the expected frequency...
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    Looking for an ultra-low noise OpAmp [TIA]

    Hi fellas, I'm working on electronics related with low noise technologies and I want to improve a previous design of a Transimpedance amplifier which used the OpAmp LMH6624. I was looking for really different stuff from the same and other manufacturers, checking if they released new models...
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    How does LTSpice measure the inoise in noise simulations? [Ouput dependant result]

    Hi everybodoy, I've got a doubt concerning the use of noise simulation in LTSpice. As far as I know, the input current noise density (inoise in LTspice) is the equivalent noise at input coming from every noise source in the circuit. I'm dealing with one schematic representing a TIA...

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