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Questions tagged [input-impedance]

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Audio amplifier setup is triggering headset button detection [closed]

I have a laptop I swapped in with an existing desk setup that includes a mixer for the audio from several computers an amplifier that I use to split the microphone from my headset between all the ...
Allen's user avatar
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Why does the author assume \$R_{in} = 1/ g_m \$ for this this circuit?

The following circuit is from Chapter 13 of Analog Design Essentials, page 1324, written by Willy Sansen. Calculate \$R_{in}\$ for this circuit. The author thinks \$R_{in} = 1 / g_m\$ However, $$ -...
kile's user avatar
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Load pull testing transceiver LNA input, impedance tuner DIY alternative

Transceiver vendors not always provide best components for input impedance matching in all variety of frequencies range that transceiver itself support, often provide impedance matching network ...
Tremax's user avatar
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1 answer
90 views

Connecting an op-amp to a second-stage amplifier: loading effect considerations

I designed an amplifier with an OPA838 as follows: First scenario: I want to connect the OPA838 to a next stage voltage LNA (Low Noise Amplifier). What components or circuit should I add to my output ...
Andromeda's user avatar
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1 answer
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Watching an open-collector input without disturbing it

I'm trying to control an opto-isolator (actually a photorelay such as a TLP354x but it doesn't really matter here). The problem lie in an external device (black magic box) which is also controlled by ...
VoltsAndNuts's user avatar
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1 answer
76 views

The effect of input and output impedance

This picture shows the classical feedback system and this assumption about this system. "the input impedances of both the amplifier and the feedback network are infinite and their output ...
Serkan Kaya's user avatar
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2 answers
60 views

LM3900: different input impedances in symmetric pins?

Referring to the LM3900 "Quadruple Norton Operational Amplifiers" datasheet, consider the schematic of each single amplifier at page 1. simulate this circuit – Schematic created using ...
BowPark's user avatar
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1 answer
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May I safely apply negative voltage to PIC's analog input?

For example I'd like to apply AC voltage ~3V. Could I not detect, but simply connect to MCU? I'd measure positive side as regular ADC, but I simply do not want negative side of amplitude to damage it. ...
Ri Di's user avatar
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How can we calculate complex impedance when there is capacitor in the transistor circuit?

The following is from the book book Design of Analog CMOS Integrated Circuit, Page 187. With the aid of Miller’s approximation, we have from Figure $$Z_{in} = \frac{1} {\Biggr[C_{GS} + (1 + g_m R_D) ...
kile's user avatar
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Calculate the input resistance of the circuit with Miller's Theorem

The following is from the book Design of Analog CMOS Integrated Circuit, Page 176. Calculate the input resistance of the circuit with Miller's Theorem. In order to calculate the gain. The current \$...
kile's user avatar
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Oscilloscope input clippers

The analog front end of an oscilloscope begins with an attenuation stage. Mostly they use two attenuation stages, like 1/1 and 1/50. From: Rigol Homebrew Wiki - schematics page The image above ...
Ahmet Atcı's user avatar
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4 answers
469 views

Why is the standard procedure for obtaining an equivalent circuit for bilateral amplifiers valid?

(Note that this question is related to this one, though this question represents my having somewhat better understood the "modification" alluded to in the linked question and wanting to ...
EE18's user avatar
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1 answer
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Differential input impedance derivation

I have been looking into differential amplifier circuits, differential input impedance, and common-mode input impedance. Everywhere I go (such as here or here), I see this as the solution for ...
HFOrangefish's user avatar
1 vote
2 answers
94 views

Input/output resistance for an accelerometer/Wheatstone bridge

I am looking at the MS 3028 Piezoresistive Accelerometer. This is the internal schematic of the component, as a Wheatstone bridge, which per my understanding means it's a quarter bridge with other ...
HFOrangefish's user avatar
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1 answer
64 views

Output-Z (electret) higher than Input-Z (preamp)

What happens if an electret microphone capsule (JFET in catridge) is connected to a preamp with considerably lower input impedance than the capsule's output impedance itself? ECM output Z: 2.2K Preamp ...
Domingo's user avatar
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1 answer
320 views

NE5532 as a Guitar Pedal Buffer

I’ve been trying to better understand the NE5532 and wanted to try designing some circuits with it. I wanted to do a dual-supply non-inverting guitar pedal buffer, but I’m concerned about the input ...
Eli Y's user avatar
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111 views

Complex Input Impedance of Autotransformer with Complex Load

I am interested in the input impedance Zin of an autotransformer with coupling k and complex load Z1 as shown in the picture. Does anyone know how this can be calculated? This is what I tried so far. ...
Charly's user avatar
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RF amplifier class A

I have simulated a class A RF amplifier. When I simulated the output impedance, it is around 50 Ω for the frequency range that is of interest (50 kHz to 100 MHz), now at the input impedance is around ...
DRF's user avatar
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138 views

What is the standard form for writing the second order transfer function for Input impedance?

When writing the transfer function for a system, the Characteristic equation in the denominator which carries information about the poles of the system is equated with the standard second order ...
user15174's user avatar
1 vote
1 answer
56 views

What is the resistance of this equivalent-circuit?

In order to cofigure an ADC, I need to know the input resistance to the ADC Pin of a uC, designated as R_source in the following equivalent circuit: From ...
ilja's user avatar
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1 answer
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Computing input resistance of two common-base configurations

When computing the input resistance of this common base configuration, the collector current \$I_C\$ is approximated as equal to the emitter current \$I_E\$: simulate this circuit – Schematic ...
BowPark's user avatar
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1 answer
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Does high pin impedance affect the need for resistors?

I'm designing a brushless motor controller as a hobby project. I'm using the MP6538 gate driver (datasheet here: 1), and I have some questions about pin impedance and whether or not resistors are ...
bonanza's user avatar
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2 answers
55 views

Can I pull down with 5V logic a not-level shifted (which is at 2.8V logic pulled-up) input? How to pull it up to 2.8V again, with no level-shifters?

I have a Distance sensor which has an enable pin (XSHUT pin in the diagram) which is pulled high in its own PCB module at 2.8V, to enable it to work. My Attiny85 MCU, which controls the sensor, is at ...
Rodrigo's user avatar
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1 answer
343 views

How to derive transistor input impedance?

Given the following circuit, When Ro is not infinite, from the book, ZB is given as, However, when it's infinite, the input impedance is easily obtained as the parallel combination of RB and β(re+RE)...
Arcadius's user avatar
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143 views

Transistor Re Model Input/Output Analysis

I have been trying to derive Av , Ai , Zi , Zo from a two port system model of a transistor. I know that the input voltage must be the voltage at the base to ground, and the output is from collector ...
Arcadius's user avatar
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1 answer
61 views

Weired result of Ltspice Zin measurement, Phase shift of -104°

I am trying to measure the input impedance of this amplifier to design a matching network for it. But the input impedance I get has a phase of -104° at the frequency of interest. I thought that Phase ...
Phönix 64's user avatar
1 vote
1 answer
146 views

Input resistance of an inverter op-amp circuit

I need to find the input resistance of this circuit. There are two parts of this exercise: The first one is to find the input resistance of the circuit without the capacitor. The second is to the ...
Aleat's user avatar
  • 179
1 vote
2 answers
184 views

Input resistance of an op-amp circuit

I need to find the input resistance of this circuit. There are two parts of this exercise: The first one is to find the input resistance of the circuit without the capacitor. The second is to the ...
Aleat's user avatar
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0 answers
46 views

What is the difference between these two input impedance equations?

I'm currently solving some university E&M homework problems and to solve input impedance, we were given this formula (from Fundamentals of Applied Electromagnetics 6th Ed): But when I browse ...
jacob arnold cena's user avatar
1 vote
1 answer
366 views

How to buffer (high input impedance required) a differential signal

I'm wanting a to increase the input impedance to a differential ADC. The ADC spec states that it can't handle a negative voltage lower than -100mV the ADC's supply can handle ~5V (this is a ATtiny1617)...
John's user avatar
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1 answer
108 views

How can I get the input impedance of this multistage amplifier?

I was trying to figure out the input impedance of this multistage amplifier. The input impedance of the other stages can be simplified to \$R_{i2}\$. I tried to replace T1 with the hirbid model but ...
Julian Zatloukal's user avatar
2 votes
1 answer
107 views

Why do LDMOS RF power transistors have a low real resistance?

I've been looking through datasheets for RF LDMOS amplifiers for use in an RF power amplifier. They typically have an input impedance that has some small real part of the resistance (<10 Ω) with a ...
cEEa's user avatar
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0 answers
57 views

Impedance of antenna and noise propagation

I would like to better understand how noise is radiated. Suppose the circuit under study is a circuit with a DC/DC converter (source of noise) and an analog circuit (receiver) which is very sensible ...
Jess's user avatar
  • 2,454
3 votes
1 answer
51 views

Input impedance when an opto-isolator is in series

My circuit is detecting 24Vac/dc signals with an opto isolator at the input. HCPL354 is the opto isolator and I am adding 4.4Kohms resistance in series to limit the current. When I make the datasheet ...
Anand's user avatar
  • 31
2 votes
3 answers
175 views

Measuring variable impedance

I was wondering how to design a measurement system that's able to correctly measure a load impedance that can vary over time and can possibly have very low as well as very high values (see figure ...
Likely's user avatar
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2 votes
1 answer
94 views

When should an unmatched antenna be measured with a cable length in even multiples of a half-wavelength?

A few years ago someone told me that if you use a cable which has a length of an even half-wavelength multiple for the frequency being tested, then the impedance measured at the end of that cable will ...
KJ7LNW's user avatar
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4 votes
2 answers
789 views

How to lower input resistance of buffer (unity-gain) op-amp?

A practical op-amp connected in a unity gain configuration will have a very high input resistance (mega-ohms or higher). How can I add an external resistor to modify the input resistance to the kilo-...
Hani908's user avatar
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1 answer
50 views

ADC input impedance - DC682a with sensor

I need to read sensor position with 16 bit resolution, with this spec: I currently have in hand the DC682A ADC, but Im not sure if I can use it from datasheet LTC1859: "The input impedance is ...
Knowledge's user avatar
  • 441
0 votes
2 answers
162 views

Input impedance of op-amp

How can I calculate the input impedance of this circuit?
moonjy1120's user avatar
2 votes
1 answer
89 views

Understanding the discrepancy between the input impedance of a signal analyzer and the input noise

The manual of a signal analyzer I am working with states that the input impedance is \$ 1 \ {\rm{M\Omega}} + 50 \ {\rm{pF}} \$, the manual also states that the input noise is \$< 10 \ {\rm{nV_{rms}/...
user27119's user avatar
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1 vote
0 answers
112 views

Not sure about input impedance of this PNP transistor circuit

I have to find the input impedance Zi of the following circuit: Using the small signal equivalent for the transistor, I get the following schematic: It is easy to see, that we need to write the ...
neil_huygens's user avatar
0 votes
1 answer
279 views

How to measure the input impedance of a laser diode/LED using a VNA?

It would be nice to have some advice on an issue I'm having with a laser diode. I have a DFB laser diode that has no kind of series resistor connected to it in the package. I want to make a driver for ...
Ravi Pradip's user avatar
0 votes
2 answers
152 views

Find input impedance in calculation and simulation [closed]

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? ...
kxdxzr's user avatar
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4 votes
0 answers
279 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, ...
TheUnknown's user avatar
1 vote
0 answers
73 views

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 ...
tobalt's user avatar
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1 vote
2 answers
186 views

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 ...
anyfoo's user avatar
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0 votes
1 answer
272 views

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}{...
Maha Mostafa's user avatar
0 votes
1 answer
4k 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 ...
Y.OU's user avatar
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2 votes
2 answers
498 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 ...
Domingo's user avatar
  • 109
0 votes
1 answer
248 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 ...
jake9wi's user avatar
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