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Questions tagged [input-impedance]

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2answers
71 views

Input impedance of circuit

Given current gain (hfe = 100), internal resistance (hie = 2000), reverse voltage gain and output resistance (hre = hoe = 0), compute input impedance for the following circuit. The problem is that it ...
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2answers
159 views

Is static negative resistance practically available?

I learned that negative resistance (NR) could be simulated by involving active devices like op-amps and others. I'm interested in the static/absolute NR rather than the differential NR. My question is ...
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2answers
52 views

Finding input impedance of the circuit

I'm having difficulties finding complex impedance of the following circuit: What I did first is find the impedance of \$C\$ and \$R\$ in parallel, which is: $$\underline{Z}_{CR}=\frac{R}{1+j\omega CR}...
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1answer
43 views

Input impedance of common-collector configuration

We have been asked to find the input impedance of the given circuit (above) I've done the small signal representation of the circuit which is as follows The question is : I tried to solve it i'm ...
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1answer
89 views

Input Impedance of a diode connected MOSFET

I was trying to derive the small-signal input impedance of a diode-connected MOSFET (figure included), and came up with this expression. Is my method correct? I have been reading about methods of ...
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1answer
34 views

What does it mean if input impedance given as a current regulator?

This SSR relay has an input impedance given in its datasheet as: It says "Nominal Input Impedance is a current regulator". At 5V 16mA. But how can I model this type of input impedance? I will use ...
-1
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1answer
51 views

Removing the imaginary part of input impedance of a Monopole in HFSS

I am building a Monopole in HFSS for my project. Its structure is shown here : The input impedance at the desired frequency is : Now i need to eliminate the imaginary part , so that the voltage and ...
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4answers
158 views

What is the Gain, Input and Output Impedence in this circuit?

So I'm trying to know what the input, output impedence and gain is in this circuit To begin, I'm kind of confused since I don't know if those two resistors at the right are in series or in parallel.
2
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3answers
136 views

Transmission Line Effects

My question has to do with the rule of thumb we generally use when dealing with transmission lines. We say that if the length of the line is 10% or less of the wavelength, we could neglect the ...
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0answers
82 views

fast voltage follower (from datasheet of LM318) and current of input terminals

I was looking at the datasheet of LM318 and found the op-amp configuration below (first image). I think the voltage at input terminal 2 is V input. But I wasn't able to figure out what V out is going ...
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0answers
34 views

low impedance as GND and current measurement, applied voltage sharing the same lead

(Image 1 is for the general idea, image2 is for questions 1 and 2, image 3 is for the 3rd question) In the setup shown below, the tuning fork is driven by an AC voltage source being connected to one ...
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1answer
98 views

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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1answer
56 views

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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0answers
203 views

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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0answers
54 views

Impedance matching in practice

I'm designing a PCB antenna with integrated circuits. Again the problem is impedance matching for maximum power transfer between the antenna and the circuits. To match the impedances I've got to ...
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1answer
40 views

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 ...
0
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1answer
102 views

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 ...
3
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2answers
103 views

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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2answers
61 views

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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2answers
167 views

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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1answer
114 views

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) ...
4
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3answers
748 views

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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1answer
201 views

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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4answers
294 views

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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3answers
208 views

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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1answer
361 views

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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2answers
557 views

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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3answers
222 views

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. ...
2
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2answers
777 views

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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1answer
232 views

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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4answers
401 views

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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3answers
6k views

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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1answer
81 views

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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1answer
75 views

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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1answer
170 views

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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1answer
266 views

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) ...
2
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1answer
141 views

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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3answers
706 views

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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2answers
276 views

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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0answers
88 views

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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1answer
350 views

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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2answers
131 views

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 ...
3
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1answer
190 views

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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1answer
2k views

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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2answers
412 views

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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0answers
599 views

about transistor input and output impedance in LTspice

I have a problem when simulate transistor's input and output impedance in LTspice. In my circuit, the correct input impedance looking into the base is about 8k, and the output impedance looking into ...
3
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3answers
804 views

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 ...
3
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1answer
2k views

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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1answer
2k views

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 reliability of you measurement, it would make sense to me to if ...
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3answers
838 views

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 ...