Questions tagged [input-impedance]
The input-impedance tag has no usage guidance.
248 questions
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Input impedance of Op amp calculation
As a part of my project I created an CMOS Op amp and I want to go through all parameters. In Op amps data sheet there are terms like input bias current and input impedance. How this terms are ...
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Inconsistent DC Input Resistance in Black Box [closed]
How It's Measured
I have a circuit (can be assumed as Black Box) I want to measure the input resistance (R2) at DC. I do the common method of using a signal (V1) with a known source resistance (R1) ...
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high input impedance circuits
Working with circuits to get high input impedance. This is to capture signals while introducing as little interference as possible to the preexisting circuit, to load the source as little as possible. ...
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Ion-selective electrode: high input impedance to measure the voltage
I read that an ion-selective electrode has an high impedance (\$100 \, M\Omega\$) and that it's necessary a high input impedance to measure the electrode voltage.
I'd like to understand the above ...
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calculate input resistance with known adc value
I am fairly new in the electronics world, but I would really like to learn it. The problem I'm facing right now, is that I miss the insight to be able to tackle this specific problem.
I have to ...
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Op-amp input impedance datasheet specification
Some op-amp datasheets specify both the differential and common-mode input impedance:
while others just specify "input resistance":
I've always assumed that if the datasheet only shows one value, it'...
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Determine the input impedances of a circuit
I'm studying a circuit with BJT's and I'm asked to determine the input resistances of the two amplification steps of the circuit. The circuit I'm analyzing is the following one:
To determine the ...
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Shouldn't internal input resistance of a transistor be almost zero?
I am absolute beginner in electronics and the whole transistor thing is not looking very intuitive to me. Suppose this problem, in active region input terminal voltage almost remains constant with ...
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Achieving high-input impedance for a voltmeter front-end
So, I'm starting on the front-end for my digital project, figured out the ratios (100kΩ, 900kΩ, 9MΩ for ÷10 and ÷100), tolerances (0.05% - 0.1%) and temperature coefficients (< 50ppm/°C might work) ...
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When talking about input and output impedances, what are we comparing them to?
Let's consider a theoretical highpass filter:
simulate this circuit – Schematic created using CircuitLab
I'm trying to show that the worst-case input and output impedance is R but the whole ...
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How to test the input impedance of a Microphone Preamp?
How would someone test the input impedance of a microphone preamp? I have all the necessary equipment i.e. oscilloscope and multi-meters but I'm struggling to find information on the topic.
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Op-amp ideal characteristics
In a textbook, it says that the ideal op-amp should exhibit following electrical characteristics and one of them is - **
Infinite input resistance (R) so that almost any signal source can
drive ...
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3
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Is the dynamic input resistance zero for constant voltages?
This might sound a stupid question but I'm confused with the following excerpt:
If Vbe is constant 0.7V which means ΔVbe is zero, does that mean the dynamic resistance is zero?
I think I have ...
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multimeter input impedance calculation discrepancies
To measure the input impedance of a multimeter, I have built a voltage divider circuit with equal resistances R1 and R2 and measured the voltage across one of them using the multimeter. Considering ...
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Input impedance of instrumentation amplifier circuit
I am trying to understand the input impedance of this circuit, which is a part of the schematic of this project.
simulate this circuit – Schematic created using CircuitLab
The circuit ...
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Is this a delay circuit? / Which resistor is responsible for load impedance?
I just stumbled upon this circuit of a microphone preamp. However, I`m not entirely sure about two of its components/ properties.
My first question regards R3 and its closely located capacitor. ...
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How measure input impedance this differential amplifier in LTspice?
How to measure the input impedance (shown in the figure below) of this differential amplifier with BJTs in LTspice?
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BJT Emitter Degeneration Rπ
I am a bit confused about this differential base-emitter resistance.
I has been said that r_pi doesn't have much influence on small signal input impedance, when CE with emitter degeneration is used. ...
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Importance of Common-Emitter Input & Output h-parameters
Speaking for NPN Bipolar transistor:
In many practical examples parallel resistance of base-emitter junction (aka hie) and finite collector-emitter parallel resistance resistance (aka hoe) are ...
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What is the difference between characteristic impedance and input impedance in transmission lines?
What is the difference between characteristic impedance and input impedance in transmission lines? When are these quantities are equal?
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Why is the input noise of an op-amp often lower than the Johnson noise equivalent to its input impedance?
As an example, the OPA227 has 3.5nV/sqrt(Hz) input voltage noise density (at 10Hz). Its input impedance is 10MΩ, which has an equivalent Johnson noise of 1μV/sqrt(Hz) at room temperature - much larger ...
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Input Impedence of Transmission Line Loop
I am practising questions from old tests for an upcoming exam on EM fields and waves. I came across this question which has me confused. I'm not sure where to start.
A lossless TL of length l and ...
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257
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Calculate the input impedance of a passive AC voltage sensor
I got a AC voltage sensor to measure AC voltage. And I want to know its input impedance. But the sensor's data sheet only tells how to use it, doesn't tell the internal details. It's used as below:
...
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436
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What is meant by "input/output impedence" of a transistor stage in amplifiers?
I am studying BJTs (bipolar junction transistors)(npn), different types of amplifiers built with these transistors and their small signal equivalents (hybrid \$ \pi \$ - model without capacitances) ...
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Function of resistor in OpAmp circuit
I came across this circuit as part of a larger circuit in a guitar effect pedal:
simulate this circuit – Schematic created using CircuitLab
I was wondering about the function of the resistor \$...
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How to differ output & input resistance of small-signal model BJT?
I understand how input and output resistance of small-signal model for bipolar transistor is defined and how draw one.
What I don't understand quite yet is how actually input and output resistance of ...
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2
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687
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Confusion with a measurement method suggested for an opamp input impedance
Before asking my question, I want to show the probe and scope model I use in the simulation:
In the above schematics the section inside the rectangle represents a scope probe set for DC coupling at ...
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Clarification about the effect of feedback resistor on the input impedance of an inverting amplififer
Below is a typical inverting op amp topology:
I was about to answer to this question, but I wasn't sure about the conclusion and couldn't find a supporting document so far.
Normally in tutorials ...
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Single input impedance of long-tailed pair
I have following circuit:
and I'd like to know input resistance of single input Ui. I tried to calculate it like this:
if I increase Ui by little, there's some voltage drop on base-emitter junction (...
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2
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248
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Inverting input causing current draw on non-inverting input?
Problem: unexplained current draw on non-inverting input when voltage on non-inverting input is above the inverting input.
Background:
I have been playing around with an RC timing circuit from pg. 24 ...
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Can I "duplicate" a stereo signal to 5 channels? Are there any impedance issues?
A friend of mine has an old 5.1 audio system. The amplifier of the system has 5 cables as inputs to be connected to the audio source.
My friend actually uses some cable splitters to send the stereo ...
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Converting S parameters to Z parameters - divergence
I have cause to convert some Z parameters to S parameters and vice versa. Here is the conversion for \$Z_{11}\$;
$$Z_{11} = {((1 + S_{11}) (1 - S_{22}) + S_{12} S_{21}) \over \Delta_S} Z_0$$
where
$...
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Is high impedance important for a differential amp measuring a battery voltage?
I want to measure voltages of multiple cells which are connected in series. I want to do that using a differential amplifier. I read about low input impedance, and what to do about it in this case. So ...
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Why do we care about matching the input impedance of receiving RF amps?
Lets say we have a receiving antenna that intercepts a certain amount of power \$P_r\$ = \$SA_r\$, where \$S\$ is the power flow density of the incoming EM wave, and \$A_r\$ the effective area of the ...
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Input and Output Impedance parameters of two port network
I am reading about two port network and I come to about Z-parametrs
$$\begin{bmatrix} \mathbf{V_1} \\ \mathbf{V_2} \end{bmatrix}=\begin{bmatrix} \mathbf{Z_{11}} & \mathbf{Z_{12}} \\ \mathbf{Z_{...
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Multimeter current measurement: internal resistance or input impedance specification
As the internal resistance (or input impedance) of a multimeter influences the circuit you are measuring, and therefore influences the accuracy of your measurement, it would make sense to me to if ...
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Input impedance oscilloscope
I am using Keysight MSOX3102T oscilloscope which has 1 GHz bandwidth. At these frequencies, \$1~M\Omega\$ input impedance is not suitable due to reflections. Therefore, it has the possibility to ...
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Calculation and measurement of input and output impedances of a Class-D amplifier
How would I calculate, from datasheet information or elsewhere, the input and output impedances of a Class D power amplifier, in general or for say a chip like the LM4670 or the TPA2000D1?
{Note that ...
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How to set Rin & Rfb to optimize input impedance / Johnson noise of an opamp circuit?
This question follows great answers I got for my previous question about GBW. It teaches me I should use two stages in my microphone preamp project. This leads me to this question:
Considering the ...
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Arduino Nano: How to decide voltage divider values that are safe for the input of the ADC [duplicate]
I am building a simple voltmeter circuit that needs to measure up to about 35 volts. Looking around the web, I am finding all sorts of suggestions for voltage divider values, like 1 Mohm / 10 Kohm, ...
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How do you bring up the equations for this Op-Amp numerical question?
How do you make the KCL/KVL equations for this circuit? Does input impedance means calculating overall circuit impedance?
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Emitter-Follower Base Input Impedance
I am trying to solve this circuit and am getting confused by how the input impedance of the base of the transistor is calculated. I am confused how this is done? What are the general rules for ...
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Input impedance butterworth filter with multiple feedback
I have a problem finding the input impedance of a Butterworth filter. The circuit is shown in the figure below:
I have calculated the transfer function between input and output; but now I have to ...
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Impedance of an antenna
I need to calculate input impedance of an antenna. What I've got is frequency, SWR magnitude, phase, return loss and impedance of transmission line. As far as I know, as a result I should get complex ...
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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 ...
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Finding Input Impedance of a Gyrator
I'm attempting to complete the question below.
What I understand so far: The circuit can be modeled with an 'equivalent inductor' and gain stage (not sure if this models the whole circuit or just one ...
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attiny84 input resistance
Looking at the datasheet for the attiny family, you find something called 'reference input resistance'. (Datasheet: http://www.atmel.com/images/Atmel-7669-ATtiny25-45-85-Appendix-B-Automotive-...
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Impedance matching at the CMOS input
I have some doubt regarding the working of series termination resistor for impedance matching purpose.
For an example, i am feeding a 50MHz clock to the clock buffer ic PL133-37 input, i have seen ...
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Why aren't all audio inputs Hi-Z?
This is sort of a follow-up on this question: How important is impedance matching in audio applications?
So if impedance matching is not important, why don't we use say 1M inputs for line level ...
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Raspberry Pi 3 GPIO Input Offset Current Specs?
I'm using a Raspberry Pi connected to a custom breakout board.
I'm reading in low power signals from an analog opto-isolator and was wondering if there are any specifications for the GPIO pins such as ...
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