Questions tagged [input-impedance]

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Find input impedance in calculation and simulation

May I ask how to find the input impedance for the output of VG1 in the calculation and in simulation tests? Should I consider the op-amp as a resistor with the ideal input impedance when calculating? ...
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34 views

Common base amplifier's input impedance

simulate this circuit – Schematic created using CircuitLab In a BJT common base amplifier configuration the input impedance is ~\$r'\$ (emitter resistance), right? If I understand correctly, ...
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Cascoded op-amp: What practically limits CMRR and input impedance?

I am interested to better understand the practical limitations to input impedance and common-mode rejection ratio in cascoded op-amp structures. I already simulated quite a bit, but I am running into ...
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Are frontend amplifiers in RF transceivers impedance matched?

I think by now I get complex impedance, the Smith chart, and antenna matching, but I am wondering how in an RF transceiver, i.e. a radio, the amplifiers on the transmitting and the receiving end are ...
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1 answer
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How can I determine the input and output impedance in a common base amplifier?

I have been struggling with this simple problem for a week. I want to find the input and the output impedance. We were only taught two formulas in our course to find the impedance: $$Zin= \frac{Vin}{...
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1 answer
99 views

How to practically measure an input impedance?

I would like to know how I could practically measure the input impedance of the following circuit: I update my post by adding the rest of the circuit. This is what my circuit looks like. The aim of ...
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2 votes
2 answers
331 views

Audio splitter without buffer possible?

The audio source is an active mixer with an output impedance of 100 ohm, 25 mA output current and 3 V-pp max. The inputs that would receive this source are (1) an ADC with an input impedance of 20 ...
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1 answer
50 views

Frequency Counter Input Impedance

I have been looking at RF frequency counters and noticed that they all have one port that says up to 50 MHz with an input impedance of 1 megaohm. However the +50 MHz input says 50 Ohm impedance. If ...
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1 answer
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What's the relevance of differential (and common-mode) input impedance?

Short version: as stated in the subject: what's the relevance of these parameters when designing a "normal" op-amp circuit, for example for audio: a Sallen-Keys active filter, or an RIAA-...
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3 votes
2 answers
219 views

Would appreciate some tips on designing simple OpAmp circuit

I've recently posted this question regarding input impedance when working with DC signal on HCPL-7840 Isolation Amplifier. The answers were very clarifying and helpful, but I've come to realize I need ...
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3 votes
3 answers
429 views

OpAmp input impedance when working with DC signal

I'm using an HCPL-7840 (Isolation Amplifier) on a project. Its datasheet says its equivalent input impedance is 500 kΩ, but impedance is frequency dependent and I'm going to use it in a DC application....
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29 views

Receiver stage of single ended signal impedance

I have buffered RC filter feed by single ended signal from 5m wire. Since we can scale impedances without frequency characteristic change, I now we can opt between input resistor of filter being small ...
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1 vote
4 answers
237 views

Input impedance for a difference amplifier OpAmp circuit

For the above circuit, I would like to find the input impedance for the input \$v_1\$. Assuming that \$R_1 = R_2\$ and \$ R_3 = R_4\$, then: $$v_0 = \frac{R_3}{R_1} (v_2 - v_1)$$ As far as I know, the ...
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1 answer
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solving purely resistive DC circuit using input output impedances and gain

I want to solve the following example circuit not using node analysis or other methods but calculating input impedance/output impedance and gain of the circuit. The circuit has no AC source and is ...
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S-Parameters Power amplifier impedance matching

I recently decided to conceive a 10W class 446MHz amplifier. I want to be able to amplify a 100mW signal into a 10W, for that i'm going for a two stages amplifier : SKY65162 to amplify the signal to ...
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1 answer
62 views

Lossless quarter wavelength transmission lines

so my lecturer released a past paper with the answers and I have no idea how he got the answer to this question. Please could someone explain it to me? Thanks. The question is: A lossless quarter-...
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8 votes
1 answer
905 views

What is this circuit called, and what is it used for?

I analyzed this circuit and found that it's an inverting amplifier and that the impedance of the circuit goes to zero when the frequency of the input voltage goes to infinity. Does anyone know the ...
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-3 votes
1 answer
50 views

Amplifier with bipolar transistor

What does input and output impedance (I/O) in electronics mean? This is in my book but I didn't understand it. Please explain it to me
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1 vote
0 answers
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Define input impedance of a buck converter for ideal converter (efficiency 100%) & practical converter

What I know was -The input impedance by the closed-loop buck converter in CCM mode, Zi and, in turn, that presented impedance is dependent on Zo and the duty cycle used by the buck converter below is ...
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0 votes
3 answers
310 views

Explanation about op-amp bias resistor and bootstrapping

I am reading a book on op-amp and its applications in linear-integrated circuits and came across this topic of creating an op-amp circuit with very high input impedance. I believe that I understand ...
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1 vote
1 answer
111 views

What is the input impedance of the ADC the SAMD21 on the Arduino Zero?

I'm looking through the data sheet and I can't find the answer. Datasheet
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0 answers
51 views

STM32G0 Seems to output 0.77 V on the input pin when set to high impedance and nothing else is connected to it, why does this happen?

Currently I have an a pin on an STM32 set to be an input and floating (high impedance). When the device it was measuring from was powered down and nothing was going on I was measure about 0.35 V on ...
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1 answer
59 views

Impedance sensing technology with headphone extension cord [closed]

I have a simple question and I've tried researching the topic but I don't understand the technology. My computer uses impedance sensing technology to set the impedance for headphones. My situation is ...
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2 votes
1 answer
212 views

How stable is Pull-up / Pull-down resistance in newer microcontrollers like SAM D21?

I'm working on a low power design using SAM D21 microcontroller (Adafruit Feather M0). I would like to take advantage of configurable I/O and have it normally in high impedance state, but reconfigure ...
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3 votes
1 answer
122 views

Is input leakage current a valid way to calculate the input resistance of a digital input on a microcontroller?

I'm trying to calculate the value of a resistor to protect a digital input on a microcontroller (10Ω and 1kΩ in the image below): The microcontroller datasheet (PIC16F1718 Datasheet) doesn't specify ...
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1 answer
113 views

A simple circuit of NOT using a buffer

First of all, I am new to the area of electronics and I want some help to stuff that may sound to you a little obvious. I've seen a circuit using transistor that is used as a NOT logic gate, as in the ...
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1 vote
2 answers
72 views

How do I incorporate output and input impedances connected to my circuit?

I'm designing a TTL to VGA DAC for a vintage PC, and I'm confused about the significance of the output and input impedances of my video card and monitor, respectively. The VGA spec states 75 ohms at ...
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3 votes
1 answer
130 views

Input protection for instrumentation amplifier

There were a few concepts mentioned in the Input Protection Basics from A Designer's Guide to Instrumentation Amplifiers, page 5-5 that I don't quite understand: Why direct transient to power supply ...
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1 answer
63 views

Why reactive components have less influence at low frequencies?

Some textbooks state that reactive components (may) have less influence at low frequencies, since inductance and capacitance are generally more significant at hifh freqs. "Pratical electronics ...
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2 votes
1 answer
2k views

How to calculate input impedance for this simple circuit?

I'd like to calculate the input impedance of the following circuit, assuming that Q1 is "active". I know that the impedance of the voltage divider is \$\frac{R_1R_2}{R_1+R_2}\$ and the ...
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1 answer
74 views

Why is input resistance parallel with the base of BJT?

I'm solving for the third stage. The resistance looking into the base of Q7 is taken between its base terminal and ground as follows during small signal analysis for single end gain of Second Stage ...
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1 answer
234 views

STM32 Input Pin not working

i try to implement an input which is reacting on an high impedance 3.3V on PC14. My Configuration looks like this. ...
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2 answers
190 views

Why do op amps need input protection when the input impedance is very high?

From what I understand, the input impedance of an op amp is very high (ideally infinite) and almost no current flows into the op amp. If that is the case why do we put a resistor in series with the ...
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4 votes
1 answer
315 views

What's wrong with my diode SPICE model for the HSMS-2860?

To be brief, I am as new as they get to creating SPICE models for components so I'm walking blind. I was trying to create a SPICE model for the HSMS-2860 diode. HSMS-2860 Schottky Diode Datasheet Here ...
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0 votes
1 answer
237 views

Input impedance of GPIO pins vs. current protecting resistor

Novice here. I have read that the input impedance of GPIO pins on a microcontroller might be in the order of 20 megohm. I’m trying to understand why we then might need a current limiting resistor with ...
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1 vote
1 answer
71 views

Finite input impedance of voltmeters

I have a question regarding the impedance of voltmeters. I learned that a voltmeter can be modeled as follows, where \$R1\$ is the input impedance: simulate this circuit – Schematic created ...
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0 votes
1 answer
80 views

Ideas sought for RF impedance selection

Context I'm designing an audio amplifier input stage. This amplifier is fully differential. Among other things, one of the design goals is to have good CMRR for UNbalanced (single ended) inputs with ...
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1 vote
1 answer
94 views

Buffer amplifier and input impedance

It is said that the input impedance of a buffer must be high enough so that it can isolate its input voltage and carry it to its output for driving purposes. What I do not understand is why we treat ...
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2 votes
2 answers
103 views

What "was" input resistance of this voltage-voltage topology amplifier before feedback?

I'm slowly working my way through understanding negative feedback in simple BJT amplifiers. I'm studying this circuit here: I read that one of the advantages to negative feedback in this topology is ...
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0 answers
54 views

NPN BJT common emitter amplifier input impedance

I am trying to find the input impedance of this circuit. In this circuit 10K resistor is load. I looked at my book but could not find any circuit looking like this because none of them has C1 ...
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0 answers
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Can I replace a music toy speaker with a 6.3mm jack?

This toy keytar gas an 8 ohm speaker and adjustable output volume. If I simply replaced the speaker with a 6.3mm jack to use it with guitar pedals and speakers that can handle the line level, would I ...
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1 answer
59 views

Why does my single-supply non-inverting amplifier produce a wierd shape (depending on earphones)?

I built this circuit: It is based on this design for a single-supply non inverting amplifier: When I tested my output waveforms with earphone A I got normal results: When I used earphone B, I got ...
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0 votes
0 answers
87 views

How do we calculate the input impedance of an op-amp?

Question: 1.3 1.4 How would I calculate the input impedance in the diagrams above? This is what I have tried in my exam, however I got this wrong, and my teacher had told me not to take into ...
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0 votes
0 answers
166 views

What is Input Impedance Mismatching of differential Operational Amplifier?

I am new to design differential op-amp. I am not sure if my circuit will experience input impedance mismatching. Can anyone explain how input impedance mismatching will happen in differential op-amp? ...
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-2 votes
2 answers
109 views

calculating the the input impedance with the effect of ro

How could he calculate zb with the effect of resistance of ro? Here he calculated zb without the effect of ro and i have understood that.
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1 vote
0 answers
41 views

Voltage regulation at full load

The voltage regulation is I(Rcosa -Xsina)/Vr For leading pf Here %of regulation=(VRcosa-Vxsina)/Vr ×100 %=((4×0.8)-(6×0.6))/100 ×100% =-0.4 Where I am doing wrong?
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1 vote
1 answer
257 views

How do analyze input impedance of Class AB amplifier biased with resistors?

EDIT: I realize that the original circuit is deeply flawed and will burn up upon re-entry. Thanks to anyone who can help me understand why! I'm learning to analyze Class AB amplifiers, but haven't ...
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1 vote
1 answer
52 views

What equation do I use for simple class AB input impedence?

I'm a novice at this. I've done some figuring and would love to know if I've got this correct before I move to more complicated circuits. I have the simplest Class AB amplifier and I'd like to know ...
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2 votes
2 answers
2k views

High-Z input in audio interface

In audio interfaces (e.g. USB) you often find one input that can handle XLR and jack. The jack input is usually used for an electric guitar input. For that, there is a "High-Z" switch to it. ...
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3 votes
2 answers
514 views

How do you match an LDMOS FET to 50 Ohms?

I'm considering using one of the following LDMOS FETs as an RF amplifier: AFM907N (8W) AFT05MS031NR1 (30W) AFT05MP075NR1 (70W) The datasheets provide \$Z_{source}\$ and \$Z_{load}\$ metrics for some ...
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