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Questions tagged [input-impedance]

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13
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3answers
1k views

Why are oscilloscope input impedances so low?

My question is two-fold: Where does the input impedance come from? I'm wondering where the input impedance of your average multimeter or oscilloscope comes from? Is it just the input impedance to ...
1
vote
1answer
47 views

Input impedance of differential amplifier

Can someone please explain to me, how I should look at the input impedance of the opamps, seen through the voltage \$V_1 V_2\$? I have two questions on the differential amplifier: Why doesn't the ...
1
vote
2answers
40 views

Impedance frequency response for a DC motor

Consider the following impedance frequency response for a DC motor : Its equivalent circuit is : Clearly, from the response, there exists a capacitor, inductor, and resistor, but my problem is how ...
-2
votes
1answer
65 views

How do I find input impedance here?

I'm not too sure how to go about doing this. Added what I did so far but I don't know where I messed up.
0
votes
2answers
49 views

Input Bias Compensation Resistor Calculation for an Integrator

I have been reading the following tech note from Analog Devices that discusses designing an op amp circuit to compensate for the input bias current: https://www.analog.com/media/en/training-seminars/...
3
votes
1answer
174 views

Impedance calculation from voltage and current (exponential) waveforms

If we want to find the impedance across two terminals (a port) at a frequency \$\omega_0\$ using the voltage waveform across \$v(t)\$) and current through (\$i(t)\$) the terminal, general intuition is ...
11
votes
2answers
544 views

How are such low op-amp input currents possible?

I understand that op-amps have low input currents; that's one of their defining characteristics. But looking at the datasheet for the LMC6001 (amusingly called an "Ultra, Ultra-Low Input Current ...
4
votes
3answers
1k views

Strange opamp's output impedance in spice

I'm simulating this circuit in Micro-Cap, which is the clipping stage of a guitar effect. The opamp model is the "NE-5532" I want to measure the input and the output impedance. I expected an output ...
0
votes
2answers
45 views

Change range of data acquisition system

I have a DAQ with many inputs that can measure within +-10 V, and I want to go up to +-30 V. Using a resistor voltage divider could be an option, but this lowers the input impedance. I would prefer ...
0
votes
1answer
29 views

Confusion between Input/Ouput Impedance and Thévenin's theorem

I'm bit confused about what Input Impedance or Output Impedance is. I tried to read Wikipedia's page (https://en.wikipedia.org/wiki/Input_impedance) but I find it hard to follow. Is the Input ...
2
votes
2answers
163 views

Emitter follower and input impedance

I'm designing an active bandpass filter (using only BJTs, voltage sources, resistors and capacitors) with the following properties: Corner frequencies \$8 ~ \text{kHz}\$ and \$800 ~ \text{kHz}\$ (...
0
votes
0answers
28 views

Correct way to calibrate SDR RX into a measuring receiver

While playing with my SDR (Software Defined Radio) Board, I was interested in performing a TX output power table at different center frequencies and TX antenna gains. However, unfortunately, I do ...
0
votes
1answer
33 views

Calculate input resistance of power amplifier

how can I calculate the input resistance of this circuit? Thank you!
0
votes
2answers
98 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 ...
0
votes
2answers
175 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 ...
0
votes
2answers
76 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}...
0
votes
1answer
76 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 ...
-2
votes
1answer
264 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 ...
1
vote
1answer
36 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
votes
1answer
102 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 ...
1
vote
4answers
164 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.
3
votes
3answers
183 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 ...
0
votes
0answers
136 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 ...
0
votes
0answers
37 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 ...
-1
votes
1answer
146 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 ...
-1
votes
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) ...
1
vote
0answers
261 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. ...
0
votes
1answer
45 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
votes
1answer
115 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 ...
4
votes
2answers
185 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'...
1
vote
2answers
63 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 ...
0
votes
2answers
236 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 ...
0
votes
1answer
153 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) ...
5
votes
3answers
1k 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 ...
0
votes
1answer
235 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.
-1
votes
4answers
340 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 ...
2
votes
3answers
307 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 ...
1
vote
1answer
498 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 ...
0
votes
2answers
680 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 ...
0
votes
3answers
243 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
votes
2answers
1k 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?
1
vote
1answer
278 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. ...
0
votes
4answers
462 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 ...
1
vote
3answers
7k 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?
1
vote
1answer
98 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 ...
1
vote
1answer
78 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 ...
0
votes
1answer
195 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: ...
0
votes
1answer
283 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
votes
1answer
159 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 \$...
0
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3answers
804 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 ...